US3477380A

US3477380A - Electric control circuit and hydraulic system for concrete pumping apparatus

Info

Publication number: US3477380A
Application number: US695464A
Authority: US
Inventors: Frederic R Johanson; Meredith E Smith Jr
Original assignee: Jaeger Machine Co
Current assignee: Jaeger Machine Co
Priority date: 1968-01-03
Filing date: 1968-01-03
Publication date: 1969-11-11
Anticipated expiration: 1986-11-11
Also published as: NL6808242A; CH498997A; BE716230A; JPS4820489B1; DE1703283A1; FR1567714A; LU56224A1; GB1192657A; ES353644A1

Description

a Sheets-Shet 1 INVENTORS ATTORNEYS C SYSTEM FOR CONCRETE mww omw mm F. R. JOHANSON ET L PUMPING APPARATUS Rm mum 54 C CONTROL CIRCUIT AND HYDRAULI ELECTRI Nov. 11, 1969 Filed J an.

MEREDITH E. SMITH, JR.

BY MA HONEY, MILLER a RAMBO BY FREDERIC R. JOHANSON Nov. 11, 1969 F, R OHNSON ET AL 3,477,380

1M FOR CONCRETE ELECTRIC CONTROL cmoux-r AND HYDRAULIC SYST PUMPING APPARATUS Filed Jan. .5, 1968 3 Sheets-Sheet 2 mm mm -m a flmu m Wm INVENTORS F REDERIC RJOHANSON MEREDITH E. SMITH JR. BY

338 g MAHONEY, MILLER a \1 1 l BYRAMBO ATTORN s United States Patent U.S. Ci. 103-49 26 Claims ABSTRACT OF THE DISCLOSURE A control system is provided for concrete pumping apparatus and the system includes a hydraulic system which effects the several operations and an electrical control circuit which controls the hydraulic system in the performance of the several operations. Fluid control valves in the hydraulic system control the cyclic operation of each of several independently operable concrete pumping units. The electrical control circuit which includes electromechanical interconnection with the several pumping units provides several modes of operation for a concrete pumping apparatus having two independently operable pumping units with the modes of operation including synchronous operation of both units, independent manual operation of either or both units, or any combination of automatic operation with respect to one pumping unit and manual operation with respect to the other pumping unit. Solid state circuitry is employed in the electrical control circuit to provide an automatic control sequence for automatic synchronous operation as well as independent automatic operation of a particular pumping unit. Manual switching elements are incorporated in the solid state circuitry which are selectively operable to bypass the automatic circuit components and permit manual operation of each or both of the pumping units at any particular point in an operational cycle and for any part of a cycle.

GENERAL DESCRIPTION OF CONCRETE PUMPING APPARATUS Pumping apparatus for handling of fluid concrete comprise in general a reciprocating piston and cylinder unit having valve means selectively positionable for placing the cylinder in communicating relationship with either a concrete supply means or a concrete discharge circuit. Mechanical or fluid power means connected with the respective concrete pump piston and valve means is selectively operable to eifect a cyclic operation of the apparatus in forcefully impelling intermittent charges of fluid concrete through the discharge conduit. In the usual apparatus, a multiplicity of pumping units are provided with two units being the normal number. The several discharge conduits are generally connected to a common discharge conduit thereby providing a combined output. Suitable control systems and mechanisms are incorporated and connected with the apparatus to effect the desired automatic operation in performing cyclic pumping of the fluid concrete from the supply means and through the discharge conduit. v

The known prior art pumping apparatus generally incorporate either mechanical control systems or electromechanical system that utilize electromechanical relays. Such system have not been found fully reliable in applications such as concrete pumping apparatus which are subjected to severe vibration and other adverse environmental conditions. Also, the known prior art systems are not fully and quickly responsive to improper operating situations such as often occur through jamming of the 3 ,477,380 Patented Nov. 11, 1969 valve means. In such instances, it is necessary to reverse or otherwise provide means for removing the material causing the malfunction.

GENERAL DESCRIPTION OF THE APPARATUS OF THIS INVENTION An improved control system is provided by this invention and includes a hydraulic actuating system and a novel electrical control circuit. The hydraulic actuating system includes hydraulic valve elements which are responsive to the electrical control circuit in effecting the desired operation of the concrete pumping apparatus. These operations with respect to the present embodiment which comprises two independently operable pumping units of identical construction but only includes the alternate synchronous operation of two pumping units automatically performing the pumping operations but selective and independent manual operation of either or both pumping units throughout a complete pumping cycle or any part of a cycle. The electrical control circuit and hydraulic system also permits manual operation of a pumping unit to cause a flow of concrete in a reverse direction as well as independent operation of either the pumping piston or the concrete control valve element which facilitates removal of materials or movement of materials or obstructions that may cause jamming or stopping of a pumping unit. The electrical control circuit includes solid state switching components and solid state logic or gate circuits to .perform the automatic operations of the apparatus in a novel circuit to thereby eliminate the necessity of electromechanical components such as the conventional relays. The hydraulic system also provides lubricaton of the concrete pumping cylinders with the lubricating being automatically performed in conjunction with the operation of the pumping units. Lubrication advantageously occurs at only one point in the cyclic movement of the pumping piston and which point is immediately prior to the start of a pumping stroke. a

The present apparatus also includes concrete agitating means in the supply hopper to prevent separation of the fluid concrete with this means being hydraulically operated. The hydraulic system includes control valve means permitting selective control of the agitating means with primary electric control in the electrical control circuit.

These and other objects and advantages of this invention will be readily apparent from the following detailed description of an embodiment thereof and the accompanying drawings. I I

In the drawings:

FIGURE 1 is a diagrammatic illustration of a concrete pump apparatus embodying this invention which includes two independently operable pumping; units and which drawing schematically illustrates a portion of the hydraulic system. i

FIGURE 1a is a schematic diagram of the fluid control circuit in the hydraulic system for the pumping apparatus with the conduit continuations relative to FIG- URE 1 indicated by the identifying numerals as applied to the respective conduits. i 1

FIGURE 2 is a schematic diagram of the electrical control circuit for the apparatus.

A concrete pump apparatus embodying the improved control system of this invention is diagrammatically illus-' trated in the several figures of the drawings. The illustrated apparatus is exemplary of the type having two independently operable pumping units generally designated by the numerals 10R and 10L with thesubscripts R and L indicating the unit being located at the right and left or may not include means for self-propulsion. Each pumping unit embodies the same construction and similar numerals are, therefore, applied to the identical components.

Basically, each pumping unit comprises an elongated concrete pumping cylinder 11 having a pumping piston 12 of a construction suitable for concrete pumping apparatus reciprocal within the cylinder and concrete control valve means 13. The control valve means 13 includes a valve housing 14 in fluid communicating relationship with the pumping cylinder 11 and a valve element 15 movably supported within the housing. The valve housing 14 is also provided with an inlet .orifice 16 and an outlet orifice 17 forming valve seats for the valve element 15 when positioned in association with the respective orifice. Connected with the valve housing 14 in communicating relationship with the inlet orifice 16 is a concrete supply hopper 18. This hopper projects upwardly from the valve housing to facilitate gravity flow of the fluid concrete mix into the pumping cylinder and is of adequate size to hold sufficient concrete for continuous operation of the apparatus and allowing for intermittent charging of the hopper from a suitable source, such as the well-known transit mixer. While each pumping unit 10 is shown as provided with its own independent supply hopper 13, it will be readily apparent that the supply hopper 18 for a combined unit may be of unitary construction thereby facilitating the charging operation. Connected with the valve housing 14 in communicating relationship with the outlet orifice 17 is a tapered discharge conduit 19 with both discharge conduits conveniently connected to a common discharge duct 20 having a discharge opening 21. In the conventional utilization of such a concrete pumping apparatus, a flexible conduit (not shown) of suitable length would be connected to the discharge duct 20 at the discharge opening 21 and will thus permit placement of the concrete at a desired remote point. The details of mechanical construction of such concrete pumping apparatus is well known and reference may be had to other readily available publications for such constructional details; therefore, further details are not believed necessary in this description for a complete understanding of this invention.

Reciprocating operation of the pumping pistons 12 within the respective cylinders 11 is effected by independently operable fluid motors designed as MP1 and MP2. Each fluid motor includes a cylinder 25 secured in fixed relationship to a supporting structure and a piston 26 reciprocal within the cylinder. An elongated piston rod 27 connected to the piston 26 also connects at a pinned joint 28 with the pumping piston 12. The cylinder 25 is also preferably connected to the supporting structure by a pivoted or pinned joint 29 to permit the assembly to accommodate structural misalignments that may occur in manufacture or operation. Connection of a conduit at either end of the cylinder 25 to an appropriate source of pressurized fluid will cause displacement of the piston 26 in the desired direction and consequent movement of the pumping piston 12.

Operation of the valve means 13 is also controlled by a fluid motor MP3 or MP4 as respectively connected with either the right or left pumping unit 10. Each fluid motor MP3 and MP4 also includes a fluid cylinder 31 and a piston 32 reciprocal within the cylinder 31 and having an elongated piston rod 33 connected thereto. One end of the cylinder 31 is also connected by a pivoted joint 34 to the supporting structure to accommodate the arcuate movement involved in moving the concrete control valve element 15. The free end of the piston rod 33 is connected to the valve element 15 by a lever arm 35 with the valve element and lever arm being rigidly interconnected by a valve shaft 36 rotatably supported by the housing 14. Retraction of the piston rod 33, as indicated with respect to fluid motor MP3, will thus position the valve element 15 in closing relationship to the inlet orifice 16 while extension of the piston rod, as illustrated in connection with fluid motor MP4, will swing the valve element 15 into closing relationship with the outlet orifice 17. The lever arm is also pivotally connected at 37 to the free end of the piston rod 33 and thus accommodates arcuate movement of the mechanism.

The concrete supply hopper 18 is preferably provided with agitating means, indicated generally at 40, for maintaining proper consistency of the fluid concrete mixture and preventing separation of the aggregate particles as to relative sizes. An agitating means 40 is illustrated diagrammatically in FIGURE la and is seen a comprise a revolving beater assembly 41 mounted for rotation of a shaft 42 extending horizontally through the hopper 18 and drivingly connected to a drive motor MP5. The drive motor 43, in the present embodiment, is a fluid motor of a rotary type having an output shaft connected by a suitable belt or chain and sprocket drive wheels 44 to the shaft 42. Specific constructional details of the agitating means 40, particularly the beater assembly, are not illustrated as such apparatus is well known.

Supplying hydraulic fluid under pressure for operation of the several fluid motors is a fluid supply means, indicated generally at 46 in FIGURE 1. In accordance with this invention, three independent fluid pumps PP1, PFZ and PF3 are utilized to supply the hydraulic fluid at the desired pressures. These fluid pumps may be of any suitable type although the type utilized in the present embodiment are of the fixed displacement type. Mechanical power for driving of the three pumps may be provided by any suitable means although in a portable of mobile type apparatus this motive power is supplied by either a single internal combustion engine 47 divingly connected to each of the three pumps by mechanical coupling apparatus (not shown) or a separate engine of appropriate power rating may be provided and connected to each of the several pumps. In the case of portable apparatus, the engine 47 may also be the same engine that provides propulsion power for the vehicle. A hydraulic fluid reservoir 48 of adequate capacity for the apparatus is connected by a suction conduit 49 to the inlet port of each of the respective pumps PP1, PF2 and PF3. The outlet ports of the respective pumps are connected into the hydraulic circuit by

fluid supply conduits

50, 51 and 52. Monitoring of the operation of the apparatus during the pumping operation is facilitated by the hydraulic

fluid pressure gauges

53 and 54 which are connected to the outlet ports or supply conduits of the pumps PP1 and PP2. These two pumps, as will be subsequently explained in further detail, supply the motive force for the respective right and left pumping units 10R and 10L. A third fluid pressure gauge 55 is connected by a pilot line 56 into the hydraulic circuit, as will be apparent by reference to FIGURE 1a, to determine the pilot pressure provided for control of the apparatus by the fluid pump PP3. Return fluid conduits from the various elements of the control system are connected to a fluid-return manifold 57 having an outlet port connected by a return conduit 58 to the reservoir 48. A fluid filtering apparatus 59 is connected in this return line. A fourth fluid pressure gauge 60 is provided to further facilitate monitoring of the operation of the apparatus with this gauge being connected by a conduit 61 to the return manifold 57 to detect back pressure that may build up in the system due to the filter condition and thereby indicate when the filter needs cleaning. Four main

fluid return conduits

62, 63, 64 and 65 connected with the hydraulic circuit connect to inlet poi-ts of the manifold 57 for return of hydraulic fluid to the reservoir.

Control of fluid flow to the several fluid motors of the apparatus is effected through a control valve assembly indicated generally at 66 in FIGURE 1a. This control valve assembly may advantageously be of a manifold-type construction wherein the several valve sub-assemblies re quired for control of operation of the apparatus are of similar interfltting configurations having interconnectable fluid passageways formed in the body of the sub-assemblies with the interconnections being indicated by the rectangular or square blocks. Two interconnecting fluid passageways which extend throughout the manifold assembly include a pilot pressure line 67 which is also connected to the external pilot line 56 and a pilot drain line 68. The pilot drain line 68 is connected at one end to the main return conduit 62 through a relief valve sub-assembly 69 with the opposite end being blocked at 68a. The pilot drain line 68 is also connected to return conduit 62 through relief valve sub-assemblies75, 76 and 77. Other fluid flow controlling valve sub-assemblies incorporated in this manifold structure are indicated at 70, 71, 72, 73, and 74. In addition to the relief valve sub-assembly 69 provided for protection of valve sub-assembly 70 and associated portion of the circuit, a relief valve subassembly 75 is provided for protection of valve sub-assembly 71 and associated circuit portions. A single relief valve subassembly 76 is provided for protection of both valve sub-assemblies 72 and 73 and a fourth relief valve sub-assembly 77 is provided for protection of the valve sub-assembly 74 along with protection of respective portions of the hydraulic circuit. Pressurized

fluid supply conduits

50, 51, and 52 are connected to respective inlet ports of the respective

relief valve sub-assemblies

69, 75 and 76 with fluid return conduit 62 connected to an outlet port of relief sub-assembly 69 and return

conduits

63 and 64 connected to ports of respective relief valve subassemblies 75 and 76.

The fluid return conduit 65 is connected to an outlet port of the valve sub-assembly 74 and a heat exchanger 78 is preferably interconnected in conduit 65 in order that provision may be made for removing heat generated in the hydraulic fluid in operation of the apparatus. This heat exchanger 78 may be of any well-known construction and include a vented tank 79 containing a quantity of suitable coolant and a heat exchanger coil 80 which is immersed in this coolant. Only a portion of the hydraulic fluid is routed from the valve assembly 66 but the heat removal capability is adequate for the apparatus.

All of the valve sub-assemblies 70-74 are of the same general construction and comprise a main valve V2, V4, V6, V8 and V and a pilot valve V1, V3, V5, V7, and V9 in each of the assemblies. Each of the main valves and the pilot valves V1-V10 is a three-position, spring centered, spool-type valve with each main valve being operated by a hydraulic actuator and each pilot valve being actuated by an electric solenoid.

The valve sub-assemblies 70 and 71 control the operation of the fluid motors MP1 and MP2 and are each supplied hydraulic fluid under pressure by the respective fluid pump PF2 and PPl. Fluid supply conduit 50 is connected to the pressure port P of valve V2 and fluid return conduit 63 is connected to the tank port T of this valve. Fluid supply conduit 51 connects fluid pump JFl with the pressure port P of valve V4 while fluid return conduit 64 connects. the tank port T of this valve with the fluid return manifold 57. Ports A and B of valve V2 are connected to opposite ends of a cylinder 25 of fluid motor MP1 by

conduits

86 and 87. In a similar manner, ports A and B of valve V4 are connected to opposite ends of cylinder 25 of fluid motor MP2 by

fluid conduits

88 and 89. The spools of valve V2 and V4 are of a type which will block fluid flow to or from ports A and B when the spool is in a center position. Thus, with the spool in a center position and ports A and B blocked, the piston 26 of the fluid motors MP1 and MP2 will be maintained in the last attained position. In this center position, however, port P is connected to port T and fluid flow is unrestricted through the valve and thus reduces the power requirements for the system. Shifting of the valve spool in either direction in accordance with the fluid pressure applied to a respective hydraulic actuator will result in prcssurizing a fluid motor MP1 or MP2 to effect a desired displacement of the piston 26 of that motor.

Connected to the fluid inlet passageway of the valve subassemblies 70 and 71 interconnecting the respective

fluid supply conduits

50 and 51 with a respective pressure port P of the main control valve V2 or V4 are the relief valve components 69a and a. These relief valve components have an outlet port connected with the fluid return conduit 62 and are set to open at a predetermined pressure and permit fluid flow through the valve. In the present embodiment of the apparatus, these relief valve components 69a and 75a are set to open when system pressure reaches or exceeds 2,000 p.s.i. This specificpressure setting is deemed adequate for the present embodiment of the apparatus and could be adjusted as necessary for the apparatus to accommodate any specific situation or for other embodiments of the apparatus. This setting has been found adequate to prevent damage to the apparatus that may result when an obstruction is encountered in the pumping unit by either a pumping piston 12 or the valve element 15.

Control over operation of the main valves V2 and V4 is effected through the pilot valves V1 and V3. Each pilot valve V1 and V3 is of the electric solenoid actuated type having the solenoids VS1, VS2 and VS3, VS4 thereof connected in the electrical circuit as shown in FIGURE 2. A pressure port P of each valve is connected to the pilot pressure line 67 and a tank port is connected to the pilot drain line 68 through passageways formed in the body of the valve sub-assembly. The A and B ports of each pilot valve V1 or V3 are connected by the illustrated

fluid passageways

81, 82, 83 and 84 formed in the respective valve subassemblies to respective hydraulic actuators of the main control valves V2 and V4. The spool of each pilot valve V1 and V3 is of a type which, when in a center position, blocks the pressure port P thus preventing loss of pilot pressure and connects the tank port to both ports A and B. With ports A and B thus vented to the pilot drain line 68 at any time the spool is centered around the hy draulic actuators of the main valves V2 and V4 will be vented and thus permit centering of the respective valve spool. It will suflice to note at this point that energization of a specific solenoid, VS1 or VS2 in the case of pilot valve V1 and VS3 or VS4 in the case of pilot valve V3, will result in shifting of the valve spool and thus effect operation of the main valve V2 or V4 as may be desired to effect a pumping operation.

Valve sub-assemblies 72 and 73 are constructed in a similar manner and include main valves V6 and V8 controlling the operations of respective fluid motors MP3 and MP4 which actuate the respective concrete control valve elements 15. Fluid pump PP3 is connected by condu1t'52 to an inlet port of the relief valve sub-assembly 76 and thence through internal passageways to a pressure port of valve V6. The tank port T of valve V6 is connected through other internal fluid passageways to the pressure port P of valve V8 while the tank portT of valve V8 is connected by internal passageways through relief valve sub-assembly 77 and valve sub-assembly 74 to the return conduit 65. The A and B ports of valve V6 are connected to opposite ends of the cylinder 31 of fluid motor MP3 by conduits 90 and. 91 while ports A and B of valve V8 are similarly connected to the cylinder 31 of fluid motor MP4 by

conduits

92 and 93. The spool of each valve V6 and V8 is also of a type which blocks ports A and B in a center position and connects the pressure port P to the tank port T. Thus, with the valve spools centered, pump PF 3 will continue to pump hydraulic fluid through conduit 52 to return conduit 65, disregarding operation of valve sub-assembly 74 for the moment. Ports A and B of these valves will be blocked with the valve spools centered and thus block the respective fluid motors MP3 and MP4 in the last attained position. Relief valve component 76a ,is also connected to the internal passageway connecting with fluid conduit 52 and has an outlet port connected with return conduit 62. This valve is also set for operation when system pressure reaches or exceeds 2,000 p.s.i. for the same operational reasons as the relief valve 69a and 75a.

Interposed in the fluid passageways of valve assemblies 72 and 73 connecting tank port T of valve V6 to pressure port P of valve V8, is a check valve assembly 95. This check valve is arranged to permit flow from valve V6 to V8 although flow is resisted by a sprirrg which biases the valve in a closed position and opens when system pressure exceeds a fluid pressure in the range of 65 to 100 p.s.i. Fluid flow is prevented in a reverse direction through the check valve. This check valve 95 thus assures a system pressure of at least 65 to 100 p.s.i. in the fluid passageways upstream from the valve and a positive fluid pressure for the pilot line 67 for operation of the main control valves V2, V4, V6, V8, and V10. Internal passageway 96 formed in the body of valve subassembly 72 connects the inlet passageway to port P of valve V6 to the pilot pressure line 67 with fluid pump PF3 thus providing the necessary pressurized fluid for the pilot line.

Operation of the main control valves V6 and V8 in controlling actuation of the fluid motor MP3 and MP4 is effected by the pilot valves V5 and V7. Both pilot valves V5 and V7 are of a construction similar to V1 and V3 having a pressure port P blocked in the center position and a tank port T which is connected to ports A and B in this center position thus venting the hydraulic actuators of the main valves V6 and V8.

Internal passageways

110, 111, 112 and 113 connect the A and B ports of the pilot valves V5 and V7 to the respective hydraulic actuators of the main valves V6 and V8. Each pilot valve is also provided with electric solenoids for actuation thereof with solenoids VS5 and VS6 in the case of valve V5 and solenoids VS7 and VS8 in the case of valve V7 being connected in the electrical circuit as shown in FIGURE 2. Energization of either solenoid of the pilot valve V5 or V7 as the case may be will thus result in actuation of the main control valve V6 and V8 for operation of the associated fluid motor MP3 or MP4 in the desired direction for appropriate movement of the concrete control valve element 15.

In accordance with invention, each valve sub-assembly 72 and 73 is also utilized in supplying lubricating fluid to a respective pumping unit 10R or 10L. This lubricating fluid for convenience of operation and simplification of the apparatus required is prefereably the same hydraulic fluid utilized for operation of the hydraulic systhem. Each pumping piston 12, which is of a conventional construction with the details thereof being shown in other readily available publications, is formed with an annular wiping band 22 of a suitable fluid-absorbing composition, such as felt, and is located on the piston a distance rearwardly of the front face. A lubrication inlet orifice 23 is formed in each cylinder 11 at a point which coincides with the wiping band 22 when the piston 12 is fully displaced to the rear of the cylinder. This is the position attained by the piston 12 at the completion of an intake stroke and just prior to initiation of a discharge stroke. A quantity of lubricating fluid is preferably injected into the cylinder at this point and will thus lubricate the cylinder walls during the discharge stroke. A fluid conduit, 98 or 99, connects each respective lubrication orifice 23 to a respective valve sub-assembly 72 or 73. Each

conduit

98 and 99 is in communication with an internal passageway 100, 101 formed in the body of the respective valve sub-assembly and is connected to the B ports of the respective pilot valves V5 and V7 Thus, it will be seen that energization of the respective electric solenoid VSS or VS7 will result in fluid flow from the pilot pressure line 67 through the internal passageway 100, 111 and 101, 113 to the

conduits

98 and 99 and subsequently to the lubrication orifices 23. It will also be noted that the hydraulic actuator of the main valves V6 and V8 are also connected to this internal passageway 100 or 101 and will be actuating the respective valve V6 or V8 concurrently with application of lubricating fluid. A fluid flow

restrictor valve

102 and 103 is also connected in each

conduit

98 and 99 to assure a positive pressure for operation of the hydraulic actuator associated with the valves V6 and V8. These restrictor valves are preferably of the fixed orifice type with the orifice size selected to obtain the desired lubricant flow to the cylinders. Also connected in each

con duit

98 and 99 is a manually operated shut-off valve 104, 105, preferably of the needle valve type selectively adjustable to provide the desired flow of lubricant, and a respective check valve 106, 107. The check valves 106 and 107- are connected to permit free flow to the lubricating orifice 23 but prevent flow of any material in a return direction and into the hydraulic system thus preventing contamination. These check valves and shut-off valves are preferably located in close physical proximity to the exterior surface of the pumping cylinder 11 for most effective operation.

The fifth valve sub-assembly 74 controls the operation of the fluid motor MP5 driving the beater assembly 41 of the agitating means 40. This valve sub-assembly includes a main valve V10 having a spool which also blocks both A and B ports when in a centered position and connects the pressure and tank ports, P and T, together for free fluid flow. Ports P and T of this valve are connected by internal passageways formed in the body of the valve sub-assembly 74 to connect respectively with the tank port of valve V8 and the return conduits 65. Thus, with the spool in a centered position, valve V10 does not interfere with operation of either valve V6 or V8. Shifting of the valve spool in either direction will connect the ports A and B to respective ports P or T and thus route fluid through the fluid motor MP5 through the interconnecting conduits 108 and 109. Relief valve component 77a is connected to the internal passageways interconnecting the tank port valve V8 with the pressure port P of valve V10 and has an outlet port connected to the return fluid conduit 62. This relief valve is set at a relatively lower pressure than the other relief valves since it is the last valve in series fluid flow relationship to valve 76 and would not otherwise function. Valve 77 may have a setting of approximately 800 p.s.i. A lower pressure setting is required for this component of the hydraulic circuit as the fluid motor MP5 is of a type requiring a relatively lower operating pressure. Control of valve V10 is effected by a pilot valve V9 which is controlled by electric solenoids VS9 and VS10. These solenoids are also connected in the electrical circuit as shown in FIGURE 2. A pressure port P of valve V9 is connected to the pilot line 67 with the tank port T being connected to the pilot drain line 68 and ports A and B are connected by internal passageway 114 and 115 to the hydraulic actuators of main valve V10. With the spool of thi valve in a center position, the pressure port P is blocked and both ports A and B are connected to the tank port T for venting of the hydraulic actuators of valve V10. Selective energization of the desired solenoid VS9 or VS10 will result in rotation of the fluid motor MFS in the desired direction. Reversal in rotation direction may be obtained by energizing the opposite solenoid.

Control over operation of the several component of the hydraulic system and mechanical mechanism is effected by an electronic control circuit illustrated in detail in FIGURE 2. This control circuit is selectively operable to provide either complete automatic operation of both pumping units, permit manual operation of either or both pumping units, or provide a combination manual-automatic control with these operations subsequently explained in further detail. Solid state circuit elements are utilized throughout the control circuit to provide a compact and rugged circuit which is capable of performing the desired operations. A further advantage of solid state circuitry is the relatively low power requirements for operation of the system which is of advantage since the power supply for this control circuit will also normally be provided by the internal combustion engine 47 driving the fluid pumps PFI, PF2 and PF3. Most apparatus for concrete pumping units are of a mobile type having a self-contained electrical power source since they are often utilized in remote locations where other sources of electrical power are unavailable or inconvenient and this power source voltage will normally be adequate for operation of a circuit utilizing solid state components.

Detailed connection of the electrical control circuit to a power source is not further shown except for indicating the connections being made at the terminals identified as 215 and 216. The voltage of a typical electrical power source for mobile concrete pumping apparatus is a nominal 12 volts which is adequate for operation of conventional solid state circuit elements. Included in the input power circuit connected across the terminals 215 and 216 is a protective fuse F and a main power disconnect switch S1. Following the switch S1 is a filtering capacitor C1 which removes any undesired ripple or other transient voltage surges that may occur in the power source. The power source is preferably of the direct current type; however, alternating current power sources may be utilized with suitable rectifier circuits connected to the output thereof and preceding the input terminals 215, 216. Following the filter capacitor C1 is a first voltage regulating stage comprising a Zener diode CR9 having a breakdown voltage rating of 18 volts which prevents large power source transients from affecting the operation of the apparatus. The cathode terminal of this diode forms a first output terminal 222 for electrical power in the control circuit. A regulated, relatively lower voltage D.C. electrical power output for the circuit is provided by a second voltage regulator stage following CR9 and which comprises the series-connected resistor 217 and Zener diode CR10. This Zener diode CR10 is selected to have a breakdown voltage rating of approximately 5 volts with the cathode terminal of the diode forming the second output terminal 223 of the regulated power supply for the 5 volts. The anodes of each Zener diode CR9 and CR10 are connected to the input terminal 216 which is also seen to be connected with a common ground terminal. Other portions of circuit will also be noted to include a ground terminal connection.

The solenoids VS9 and VS10 which operate the pilot valve V9 are selectively connectable to the 12-volt power terminal 222 by a single pole, three-position, manually operated switch S2. A movable contact of this switch is connected to terminal 222 and is positionable in either a center OFF position or in engagement with terminals connected with the respective solenoids VS9 and V810. The opposite ends of these solenoids are connected to a common ground terminal and selective energization of the solenoids will result in operation of the agitator motor MP5 in the desired direction as previously described.

Each of the electrical solenoids VSl through VS8 for operation of the respective pilot vales V1, V3, V5 and V7 are connected in circuit with the 12-volt terminal 222 of the power circuit. Controlling the energization of each electrical solenoid VSI through VS8 is a respective power switching transistor Q1 through Q8. These transistors are of the NPN type connected in series with the respective solenoid with the collector terminal being connected to the solenoid and the emiter terminal being connected to a common ground connection. These power switching transistors Q1 through Q8 are connected in a common emitter configuration with the collector-base junction being reverse biased by the 12 volts from the power circuit. With that application of a zero or reverse biasing voltage to the emitter-base junctions, it will be seen that the transistors Q1 through Q8 will be in a cut-off or non-conductive state, while the application of a forward bias voltage to the emitter-base junction will switch the respective transistor to a conductive state. When in such a conductive state, current will flow through the transistor resulting in current flow through the respective electrical solenoid VS1 through VS8. It will be noted at this point that diodes CR1 through CR8 are connected across each respective electrical solenoid VS1 through V58 to prevent or reduce arcing resulting from the switching operation of each of the respective power switching transistors Q1 through Q8.

Application of a forward, emitter-base junction biasing voltage to the respective power switching transistors Q1 through Q8 is eflected through either the automatic switching circuitry or by respective manual switches. Selection of the desired mode of operation, either automatic, manual or a combination, is accomplished through a selector switch S3 which may be conveniently located on the control console. This selector switch S3, which is manually operated, includes two separate selections having respective movable contacts which are concurrently operated and is provided with six manually selected positions. Two of these positions are indicated as OFF and prevent application of electrical power for operation of either the automatic switching circuitry or the manual switches in applying a bias voltage to the switching transistors Q1 through Q8. The remaining four positions provide either concurrent automatic synchronous operation of pumping units in the SYNC position, automatic operation of either the left-hand or right-hand pumping unit in the respectively indicated LI-I. SYNC or R.H. SYNC positions, or manual operation of both pumping units in the MAN position. In either the left or right SYNC position, the opposite pumping unit may be manually operated.

Electrical power for operation of either the automatic switching circuitry or for the manual switches in applying a forward emitter-base bias voltage to the switching tran sistors Q1 through Q8 is obtained from power circuit terminal 222 of the voltage regulator unit through either the manual control switch S4, which is a single pole, two position switch, or the remote control switch S9 which is also a single pole, two-position switch. Control switch S4 is illustrated as being in a position connecting the movable contacts of selector switch S3 to the power source and thus by-passing the remote control switch S9. With switch S4 placed in the opposite position indicated in broken lines, the remote control switch S9 will be effective in controlling operation of the apparatus. The function of either switch is primarily with respect to automatic operation of the apparatus as opening of either switch will prevent operation of the circuit and halt the pumping operation. Closing of either switch will energize the circuit and enable further operation, either automatic or manual. The switch S4 is preferably located on a control box or console located on the pumping apparatus along with the fluid pressure gauges 53, 54, 55 and 60 while switch S9 is connected as indicated by a long, electrical cable. The purpose of the cable is to permit location of the switch S9 at a remote location, such as at the delivery end of the pumping conduit 20 and thus enable the operator to readily observe the concrete pumping operation at the discharge point and control the unit in accordance with the discharge.

Manual operation of the apparatus will be considered first and for this purpose, the selector switch 53 would be positioned with the movable contact of each section SSA and ,SSB in engagement with the terminal identified as MAN. Switch section 53A is thus seen to supply electrical power to manual switches S5 and S6 associated with the right pumping unit while switch section 83B is seen to supply electrical power to manual switches S7 and S8 associated with the left pumping unit. Each manual switch S5 through S8 is a single pole, threeposition switch which is also located in a convenient location, such as the control console. These manual switches S5 through S8 are preferably of the spring-centered type which must be held in either of the other two positions. A current-limiting resistor 218 through 221 is series connected with the movable contact of each manual switch. Each of the manual switches S5 through S8 is provided with the respectively indicated terminals A, B and C with terminal C being a center OFF position. Positioning of switch S5 to engage terminal A will result in application of a positive bias voltage to the base of the transistor Q1 which will forward bias the emitter-base junction and in transistor Q1 switching to an ON or conductive state. The collector voltage will become minimal while the current increases and the transistor will continue operation in the saturation region with both the collectorbase and emitter-base junctions now being forward biased. Electrical solenoid V.S1 will now be energized and will shift the spool of pilot valve V1 to connect the pilot port P to this valve to port A and result in operation of control valve V2 to connect pressure port P of that valve with port A thereby connecting fluid motor MP1 into the hydraulic circuit in such a manner as to displace piston 12 in extending and piston rod 27. This is the discharge stroke for the right pumping unit R. As long as the switch S5 is held in the A position, transistor Q1 will remain conductive and the spools of valves V1 and V2 will remain in the described positions and thus continue movement of the piston 26 and piston rod 27 through a discharge stroke.

When the piston 26 reaches the opposite end of the cylinder of the fluid motor MP1, further movement will be prevented and fluid pressure will build up within the cylinder 25 until reaching the pre-set operating pressure of relief valve 69. When this pressure is attained, the relief valve 69 will function and return fluid to the reservoir 48. Release of switch S5 to its spring-centered position C will remove the forward-bias voltage from the emitter-base junction and transistor Q1 will then return to its OPP or non-conductive state. In the non-conductive state electrical solenoid VS1 will be de-energized and the spool of pilot valve V1 will return to the indicated spring-centered position and the hydraulic actuator of control valve V2 will be connected to the tank port T of valve V1 thus relieving pressure in the actuator and permitting the spool of the valve V2 to also return to its spring-centered position. As previously indicated, both ports A and B of valve V2 will be blocked in this center spool position and thus lock the fluid motor MP1 in the last attained position.

Positioning of switch S5 in the B position will result in application of a forward bias voltage to the emitterbase junction of power switching transistor Q2 and effect switching of this transistor to an ON or conductive state in a manner similar to that previously described in connection with transistor Q1. With transistor Q2 conductive, electrical solenoid VS2 will be energized and shift the spool of pilot valve V1 to connect the pressure port P to port B. In this position of the spool of pilot valve V1, the opposite hydraulic actuator of control valve V2 will be pressurized and shift the spool of that valve to connect the pressure port P to port B and apply pressure to the opposite end of fluid motor MP1. This will result in reverse movement of the piston 26 and piston rod 27 and provides the intake stroke for the right pumping unit 10R. Again the movement of piston 26 will continue so long as switch S5 is held in the B position and the piston has not reached the end of the cylinder 25. Also, when the piston reaches the end of the cylinder, the same action will result as previously described with operation of relief valve 69.

Manual control switch S6 operates in the same manner as switch S5; however. S6 controls power switching tran sistors Q6 and Q5. Both of these transistors are connected in circuit with the respective electrical solenoids VSS and VS6 which operate the pilot valve V5. Pilot valve V5 controls operation of control valve V6 which, in turn, controls the operation of fluid motor MP3 having a piston rod 33 mechanically connected with the concrete control valve 15 of the right pumping unit 10R. Placement of switch S6 in position A will result in switching transistor Q5 to a conductive state and thus energizing electrical solenoid VSS while positioning of switch S6 in position B will result in Q6 becoming conductve and energzing solenoid VS6. Having reference to FIG- URE la and specifically the control valve sub-assembly 72 thereof, it will be seen that energization of solenoid VSS will result in operation of pilot valve V5 and control valve V6 to displace piston 32 and in retraction of piston rod 33 of fluid motor MP3 and result in positioning of the connected concrete control valve element 15 in a position where the inlet orifice 16 to the pumping cylinder 11 will be blocked and the outlet orifice 17 will be opened for discharge of concrete from the cylinder 11 into the discharge conduit 19. Energization of solenoid VS6 will have the opposite effect, resulting in extension of piston rod 33 and shifting of the control valve element 15 to a position blocking the outlet orifice 17 and opening the inlet orifice 16. This valve configuration is indicated with respect to the left pumping unit 10L.

The manual control switches S7 and S8 associated with that portion of the control circuit effecting operation of the left pumping unit 10L may be operated in a manner substantially as described with respect to the right pumping unit 10R. Selective positioning of switch S7 in either the A or B position will result in conduction through power switching transistors Q3 or Q4 and energization of the respective electrical solenoid VS3 and VS4. These two solenoids operate pilot valve V3 and will effect operation of fluid motor MP2 in a desired direction. Similarly, switch S8, when positioned in either A or B position, will cause transistor Q7 or Q8 to become conductive and energize the respective solenoid VtS7 or VSS. The latter solenoids operate pilot valve V7 and will effect operation of fluid motor MP4 in a desired direction to operate and place the control valve element 15 of the left pum ing unit 10L in the desired position with relation to the inlet and

outlet orifices

16 and 17.

While the operation of switches S5 and S8 have been described with maintenance of the switch in either of the desired positions A or B until completion of operation of a respective fluid motor, MP1, MP2, MP3, or MP4, in performing its intended function, it will be seen that the switches may be momentarily held in a desired position and result in operation of the respective fluid motor for only a portion of that cycle. This jogging feature of the circuit is of a particular advantage in assisting the operator of the pumping apparatus to clear the cylinders 11 of obstructions through movement of either the control valve element 15 or the pumping piston 12 or both, if necessary. A further advantage of the manual control switches S5, S6 or S7 and S8, is the independence of operation of either a concrete pumping fluid motor, MP1 or MP2, or a concrete control valve element actuating motor, MP3 or MP4. With respect to a specific right or left pumping unit 10R or 10L, the pumping piston 12 or the control valve element 15 may be operated in any desired manner which may not correspond with the usual pumping operation. This feature is also of particular importance as it permits operation of the apparatus in obtaining a reverse concrete flow. Thus, with this control circuit, concrete may be withdrawn from the discharge conduit and returned to the hopper 18.

Automatic control of operation of either the right or left pumping unit or both pumping units in synchronized manner is effected through an electronic switching circuit utilizing solid state elements which is placed in an enabled condition upon placement of the selector switch S3 in either the SYNC position or the single, L.H. SYNC or R.H. SYNC positions. This switching circuit is responsive to the position of pumping pistons 12 and the concrete control valve elements 15 with respect to each pumping unit. This condition responsiveness is effected through limit switches which are mechanically interconnected with the components of each of the pumping units. In the case of the right pumping unit R, a limit switch LS1 is provided for responding to the position of the pumping piston 12 and a second limit switch LS3 is provided for responding to the position of the concrete control valve element 15. The left pumping unit is provided with similar limit switches LS2 and LS4 which respond, respectively to the pumping piston 12 and the control valve element 15.

Mechanical interconnection of the pumping pistons 12 with a respective limit switch LS1 or LS2 is effected through an elongated rod 225 secured to the piston 12 and movable with the piston. Mounted on the rod 225 in relatively spaced relationship are two

trip blocks

226 and 227 which are positioned relative to the limit switch LS1 or LS2 to engage an actuating lever arm 228 of the switches. All of the limit switches LS1 through LS4 are of the two-position type and the contacts thereof will remain in the position resulting from the last operation of the arm 228. Through appropriate positioning of the limit switches LS1 and LS2 relative to the elongated rod 225, the trip blocks 226 and 227 will result in actuation of the arm 228 as the piston 12 approaches the end of either an intake or a discharge stroke. In the case of an intake stroke, block 227 will engage the arm 228 at the end of an intake stroke while the block 226 will engage the arm as the piston 12 reaches the end of a discharge stroke. Preferably, the

blocks

226 and 227 are also positioned on the rod 225 to actuate tthe respective limit switch LS1 or LS2 just prior to reaching the end of a particular cycle in order to compensate for any delay in the electrical circuit or hydraulic system. The actual position to obtain the desired lead time is determined by the speed at which the apparatus is normally designed to operate.

In a similar manner, the limit switches LS3 and LS4 are operated by movement of the concrete control valve element to either an intake or a discharge position. Each limit switch LS3 and LS4 is also provided with an actuating lever arm 229 and is relatively positioned to the piston rod 33 to engage respective trip blocks 230 or 231 that are secured to the piston rod. As the concrete control valve element 15 is positioned to close the outlet orifice 17, trip block 230 will engage arm 229 and block 231 will engage arm 229 when the element 15 closes the inlet orifice 16. The

blocks

230 and 231 are also relatively positioned to each other and to thearm 229 to compensate for necessary lead time.

The limit switches LS1 through LS4 are schematically illustrated in FIGURE 2 with the two respective terminals designated as A and B. Each terminal designated either A or B of the four respective limit switches is connected to the 5-volt terminal 223 of the power circuit through the current limiting resistors 235 through 242 and the interconnecting electrical conductors. Each movable contact of the respective limit switches is seento be connected to a common ground terminal at 243 and the effect of the movable contact of each limit switch is to effectively ground that theminal when in engagement with that terminal. The effect of the operation of the limit switches is to either permit application of a signal voltage to the electronic switching circuitry or to remove that voltage by grounding the respective terminal.

Performing the switching functions for automatic operation of the pumping units are several logic or gating circuits and the description at this point will be limited to the circuitry associated with the right pumping unit 10R and which circuitry includes four logic or

gating circuits

200, 201, 202 and 203 and an inverter gate 211. Each of the gates 200 through 203 are of the NAND type which employ conventional well-known circuitry and utilize solid state circuit components. These NAND-gates are of a type requiring simultaneous application of two input signals to obtain an output signal and in this instance the application of a low or essentially zero input signal voltage at each input terminal will result in an output of a relatively high output voltage signal. The output terminal of each gate 200 through 203 is connected to the base of a driver transistor QlA, QZA, Q5A and Q6A which have an emitter terminal that is connected to respective power switching transistor Q1, Q2, Q5 or Q6. The collector of each driver transistor is connected through a resistor 244 through 247 to both the SYNC and R.H. SYNC terminals of section 83A of the selector switch S3. Thus, positioning of the movable contact of the selector switch associated with section 83A in engagement or in either the SYNC or the R.H. SYNC position will connect these terminals and the collectors of the respective driver transistors to the 12- volt terminal 222 of the power circuit. These transistors are also operated in a switching function and the 12 volts will apply a reverse collector-base bias and application of either a zero or negative voltage to the emitter-base junction will maintain the driver transistors in a cut-off or nonconductive state. Application of a forward bias to the emitter-base junction, as by the application of the relatively high output voltage signal from the respective NAND-gate 200 through 203, will result in switching the respective driver transistor QlA, Q2A, QSA or Q6A to an ON or conductive state. Switching of the driver transistors QIA, Q2A, QSA or Q6A to a conductive or ON state will have the same effect on the operation of the apparatus as manual operation of the switches S5 and S6. Diodes CR11, CR12, CR15 and CR16 are connected in the circuit as indicated to prevent interaction between circuit elements should the manual switches S5 and S6 be inadvertently actuated when the circuit is in an automatic operational mode and which could result in an out-of-sequence energization of the solenoids V51, V52, V55 and VS6.

While one of the inputs to the NAND circuit 200 is obtained from the circuit associated with limit switch LS1, the second input is initially obtained from a logic or gate circuit 208 of the NOR-type. This NOR gate 208 has two input terminals, one of which terminals is connected to a terminal of limit switch LS2 operated. by the opposite or left pumping unit 10L. The other terminal of NOR-gate 208 is connected to a mid-point terminal of a voltage divider circuit comprising series connected

resistors

252 and 253 with resistor 253 connected to a common ground terminal 256 and resistor 252 connected to both the R.H. SYNC and MAN position terminals 0 fsection 53B of the selector switch S3. A voltage signal will thus be applied to the input terminals of NOR-gate 208 at any time limit switch LS2 is not in a position to connect terminal LS2A to ground terminal 243 in the case of simultaneous automatic operation of both pumping units with the selector switch S3 in SYNC position and a voltage signal will be applied at all times the selector switch S3 is in either R.H. SYNC or MAN position. This NOR-gate 208 is of a design to provide a low or zero signal voltage when a high voltage signal is applied to either input terminal.

In automatic operation of the right: pumping unit with the selector switch S3 positioned in R.H. SYNC, the NOR- gate 208 provides the second low input signal voltage necessary for the NAND-gate 200 to function in providing the high output signal to forward bias the emitter-base junction of driver transistor QlA. Accordingly, in this mode of operation, automatic sequential movement of the pumping piston 12 and concrete control valve element 15 is achieved through the cyclic operation of the limit switches LS1 and LS3.

This automatic operation can be best understood through consideration of an illustrative example of a complete operational cycle. For this example, it is assumed that the electrical circuit is connected to a suitable electrical power source at terminals 215 and 216, switch S4 is in the position illustrated in FIGURE 2, the manual control switches S and S6 are in the center position as illustrated and that the function selector switch S3 has been placed in the RH. SYNC position. It is also assumed that the concrete control valve element 15 is in a position blocking the outlet orifice 17 and that the pumping piston 12 is in a fully retracted position as would be the case upon completion of an intake stroke with the piston at the end of the cylinder 11 in alignment with the lubrication inlet orifice 23. In this situation, limit switch LS3 would have been actuated to place the movable contact in engagement with terminal LS3A and limit switch LS1 would have been actuated to place the movable contact thereof in engagement with terminal LSlA. Both inputs to NAND-gate 200 are of a low value in this assumed condition resulting in a high output and forward biasing of the emitter-base junction of transistor QlA with consequent switching of both QlA and Q1 to a conductive or ON state and energization of solenoid VS1. Concurrently, the high output of NAND-gate 200 is applied to the input terminal of the inverter gate 211 resulting in a low output which is subsequently applied to one input terminal of NAND-gate 202. A grounded capacitor C3 is also connected to

gate

200 and 211 at their common junction for circuit stability. A low voltage signal is also applied simultaneously to the other input terminal of NAND-gate 202 since limit switch LS3 is in a position connecting terminal LSSA to the ground terminal 243. Thus, NAND-gate 202 also provides a high output signal which forward biases the emitter-base junction of driver transistor Q5A resulting in switching of both QSA and Q5 to a conductive or ON state with consequent energization of solenoid VS5. As previously described, energization of solenoid V55 results in actuation of control valve subassembly 72 to pressurize fluid motor MP3 to cause retraction of piston rod 33 and rotate valve element 15 to a position blocking the inlet orifice 16 as illustrated in FIGURE 1 while energization of solenoid VS1 results in actuation of control valve sub-assembly 70 to pressurize fluid motor MP1 to extend piston rod 27 and move piston 12 in a discharge stroke. Concrete that had previously been drawn into the pumping cylinder 11 will thus be forced out of the cylinder through the outlet orifice 17 into the discharge conduit 19.

Operation of fluid motor MP3 in rotating valve element 15 to the discharge position or in blocking relationship to the inlet orifice 16 will also actuate limit switch LS3 through engagement of the trip block 231 with the arm 229 to place the movable contact in engagement with terminal LS3B. This removes one of the low level inputs to NAND-gate 202 with consequent removal of the forward bias from the emitter-base junction of transistor Q5A and return of both transistors QSA and Q5 to a non-conducting or OFF state resulting in de-energization of solenoid VSS. Solenoid VSl remains energized throughout the discharge stroke of pumping piston 12 due to continued application of two low inputs to NAND-gate 200. When piston 12 completes the discharge stroke, trip block 226 engages lever arm 228 thereby actuating limit switch LS1 and placing the movable contact in engagement with terminal LSlB. This removes one of the low level inputs to NAND-gate 200 resulting in removal of bias voltage and return of transistors Q1A and Q1 to a non-conductive or OFF state and de-energization of solenoid VSl.

At this point in an operational cycle, both limit switches LS1 and LS3 connect their respective B terminals to the ground terminal 243 and thus provide two simultaneous low level inputs to NAND-gate 203. As a result, NAND- gate 203 provides a high level output signal voltage which forward biases the emitter-base junction of driver transistor Q6A with consequent switching of both Q6A and Q6 to a conductive or ON state and energization of solenoid VS6. Energization of solenoid VS6 actuates control valve sub-assembly 72 to pressurize fluid motor MP3 and cause extension of piston rod 33 with rotation of concrete control valve element 15 to an intake position in blocking relationship to the outlet orifice 17 leaving the inlet orifice to open. Concurrently with rotation of valve element 15 to the intake position, trip block 230 will engage lever arm 229 and actuate limit switch LS3 to place the movable contact in engagement with terminal LS3A. One of the low level inputs to NAND-gate 203 is thus removed with consequent de-energization of solenoid VS6.

Terminal LS1B was previously connected to the ground terminal at the conclusion of the discharge stroke and thus provided one of the low level inputs to NAND-gate 201. Actuation of limit switch LS3 at conclusion of movement of valve 15 to the intake position in connecting terminal LS3A to the ground provided the other necessary low level input to NAND-gate 201 resulting in a high level output voltage signal which forward biases the emitter-base junction of transistor Q2A. As a consequence, both transistors Q2A and Q2 switched to a conductive or ON state resulting in energization of solenoid VS2. Energization of solenoid VS2 results in actuation of control valve sub-assembly 70 to pressurize fluid motor MP1 to cause retraction of piston rod 27 and movement of piston 12 away from the discharge-inlet end of the cylinder 11 in an intake stroke. Concrete will thus flow from the hopper 18 through the inlet orifice into the cylinder 11 behind the retreating piston 12. Upon completion of the intake stroke, trip block 227 engages lever arm 228 actuating limit switch LS1 to place the movable contact in engagement with terminal LSlA and thus removes one of the low level inputs to NAND-gate 201. The output of NAND-gate 201 returns to a low level resulting in return of Q2A and Q2 to a non-conductive or OFF state. This also results in de-energization of solenoid VS2 and deactivation of control valve sub-assembly 70.

Both limit switches LS1 and LS3 now connect their respective A terminals to the ground terminal 243 and the circuit will be in proper configuration for initiation of a discharge stroke. This is the point at which this detailed description started in describing an operational cycle and a repeat cycle will be as previously described.

Operation of the left pumping unit 10L by itself may be effected by placing the selector switch S3 in a position where the movable contact of each section is in engagement with the respective terminal identified as L.H. SYNC. Circuit components for operation of the left pumping unit are the same as for the right pumping unit previously described and includes the four power switching transistors Q3, Q4, Q7 and Q8 connected in circuit with the respective electric solenoids VS3, VS4, VS7 and VS8 of the pilot valves, the driving transistors Q3A, Q4A, Q7A and Q8A, the NAND-

gates

204, 205, 206 and 207, the NOR-gate 209 and the inverter gate 213. Arc eliminating diodes CR3, CR4, CR7 and CR8 are connected across respective electric solenoids,

collector resistors

248, 249, 250 and 251 are connected in circuit with the collectors of the driver transistors and

resistors

237, 238, 241, 242, 254 and 255 are connected in circuit with the switching gates. A stabilizing capacitor C2 is also connected in this portion of the circuit as are blocking diodes CR13, CR14, CR17 and CR18 which are connected in circuit with the manual switches S7 and S8. Connections are also made to the power circuit at

terminals

222 and 223 to obtain 12 and 5 volt DC. power for operation of the circuit components. Both limit switches LS2 and LS4 are operated in the same manner as described in conjunction with limit switches LS1 and LS3 but with operations related to the movement of the piston 12 and concrete control valve element 15 of the left pumping unit. Since the circuit for operation of the left pumping unit is the same as the circuit for the right pumping unit which has been described in detail, a detailed description of an operational cycle is not believed necessary as the operation may be readily understood by reference to the previous detailed description.

Simultaneous automatic operation of both the right and left pumping unit is effected by placing the movable contacts of the selector switch S3 in a position engaging the terminals identified as SYNC. Each side of the circuit will operate as previously described and as determined by actuation of the respective limit switches in accordance with movement of the pistons 12 and concrete control valve elements -15. In this mode of operation, an input voltage signal of a high level is not continuously provided to each NOR-gate 208 or 209 by the manual circuit connections of the opposite left or right side of the circuit as the manual switches S5, S6, S7 and S8 are not connected to the 12-volt cathode terminal 222 of the power circuit as in the previously described situation where one pumping unit may also 'be manually operated. In this SYNC position, a high level input signal for each NOR-gate 208 and 209 is obtained through interconnection with the limit switch LS2 or LS1, respectively, of the circuit associated with the opposite pumping unit. As can be seen by reference to FIGURE 2, a second input terminal of each gate is connected to the A terminal of the respective limit switch and will thus receive a high input voltage signal only when the movable contact of that limit switch is in engagement with the opposite or B terminal as would be the case when the pumping piston 12 had completed a discharge stroke. This circuit interconnection maintains thet wo pumping units in an alternating, synchronous mode of operation as the pumping piston 12 of one pumping unit will not be able to begin a pumping or discharge stroke until the opposite pumping piston has completed a discharge stroke and has tripped its respective limit switch, LS1 or LS2, to the B position and will thus be capable of providing such a high level input signal.

There is a difference in the relative speed at which the piston 12 will move in performing either a discharge or intake stroke because of the different fluid volumes involved in actuating each fluid motor MP1 or MP2 in the opposite directions. This difference in fluid volume results from the piston rod 27 being in only one side of the cylinder 25 and less fluid will be required for an intake stroke than for a discharge stroke. As a consequence, both pumping units could be at the same position in their respective operational cycles at a particular instant, such as when the limit switches LS1 and LS2 are in the B position at the conclusion of a discharge stroke, and neither NOR-gate 208 or 209 would be providing the necessary low level signal to its respective NAND-gate 200 or 204. This situation would result in complete stopping of operation of both pumping units. To avoid this situation, an

inverter gate

210, 212 is connected in a feedback circuit arrangement with the respective NAND-

gates

200, 204 to maintain the second low level input signal normally supplied by the NOR-gates. Once the NAND-gates have been switched to a state where the gate provides a high level output signal, the inverter gate will supply a low level input even if the NOR-gate provides a high level output and the necessary two input signal condition 'is satisfied.

This completes a detailed description of the apparatus of this invention which includes a novel electronic control circuit and hydraulic system for advantageous operation of concrete pumping apparatus. This control circuit permits selective operation of the two independently operable concrete pumping units with selection of several operating modes possible to meet particular operating conditions. These operating modes include dual synchronous operation of both units, single or dual manual operations of the two units or any combination thereof. In the manual mode, each pumping unit may be selectively operated as to the pumping piston and the concrete control valve element to facilitate removal of materials that may be jamming the unit and preventing further operation or to effect a reverse pumping action in clearing the discharge conduit. This manual operation may be of the advantageous intermittent jogging action.

According to the provisions of the patent statutes, the principles of this invention have been explained and have been illustrated and described in what is now considered to represent the best embodiment. However, it is to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described. Having thus described this invention, what is claimed is:

1. In concrete pumping apparatus having a concrete pumping unit which includes a concrete pump cylinder and a concrete pumping piston reciprocable in said cylinder, said cylinder provided with a lubrication orifice at a point which coincides with the position of the concrete pumping piston at the completion of an intake stroke and is adapted to utilize the fluid for operation of said fluid circuit means for lubrication of the pump cylinder and pumping piston, valve means in communication with said pump cylinder for controlling concrete flow relative to said cylinder, said valve means including an inlet orifice and an outlet orifice, and a movable valve element selectively positionable to alternatively connect said pump cylinder to either of said orifices, first fluid motor means mechanically coupled with said pumping piston and selectively operable to effect reciprocable movement of said pump piston, second fluid motor means mechanically coupled with said valve element and selectively operable to effect positioning of said valve element, and fluid pump means for supplying pressurized fluid for operation of the concrete pumping apparatus:

a control system comprising (A) fluid circuit means interconnecting the fluid pump means with the fluid motor means and including (1) first fluid control valve means provided with electrical actuating means and connected in said fluid circuit means for controlling fluid flow to the first fluid motor means, and (2) second fluid control valve means provided with electrical actuating means and connected in said fluid circuit means for controlling fluid flow to the second fluid motor means, said second fluid control valve means having a fluid outlet port connected with said lubrication orifice through a fluid conduit and which is provided with pressurized fluid when said second fluid control valve means is actuated to operate the second fluid motor means in positioning the movable valve element in closing relationship to the inlet orifice of the valve means :and thereby cause fluid to flow into the pump cylinder through the lubrication orifice, and (B) electrical control circuit means connected in circuit with the electrical actuating means of said fluid control valve means for selectively controlling the operation thereof, said electrical circuit means including (1) input terminals connect-able with a source of electrical power, and (2) circuit switching means for connecting the electrical actuation means of said fluid control valve means to said input terminals for energization thereof, said circuit switching means including (a) a first circuit portion responsive to the position of the concrete pumping piston and the movable valve element of the valve means and operative to energize the electrical actuation means of said fluid control valve means in predetermined sequence for effecting an automatic concrete pumping operation with the concrete pumping unit,

(b) a second circuit portion having manually operable switches to energize the electrical actuation means of said fluid control valve means independently of each other for independent operation of the concrete pumping piston and the movable valve element, and i (0) switch means interconnected in circuit with said first and second circuit portions to connect either of said circuit portions to said input terminals to alternatively enable operation of either circuit portion.

2. The concrete pumping apparatus of claim 1 having a fluid flow restrictor interposed in said fluid conduit connecting with the lubrication orifice to limit fluid flow thereto.

3. The concrete pumping apparatus of claim 1 wherein said fluid circuit means includes a source of pilot fluid having a minimum fluid pressure, said second fluid control valve means includes a control valve connected in circuit with the second fluid motor for controlling operation thereof and provided with fluid actuation means, a pilot valve connected in circuit with said source of pilot fluid and said fluid actuation means for controlling operation of said control valve and provided with said electrical actuating means, said pilot valve having said fluid outlet port connected with said lubrication orifice through said fluid conduit with said fluid actuation means connected to said conduit, said fluid conduit having a fluid flow restrictor interposed therein to maintain pilot pressure upstream of said flow restrictor with said fluid actuation means of said control valve being connected to said fluid conduit upstream of said flow restrictor.

4. In concrete pumping apparatus having a concrete pumping unit which includes a concrete pump cylinder and a concrete pumping piston reciprocable in said cylinder,

valve means in communication with said pump cylinder for controlling concrete flow relative to said cylinder, said valve means including an inlet orifice and an outlet orifice, and a movable valve element selectively positionable to alternatively connect said pump cylinder to either of said orifices,

first double-acting fluid motor means mechanically coupled with said pumping piston and selectively operable to effect reciprocable movement of said pump piston,

second double-acting fluid motor means mechanically coupled with said valve element and selectively operable to effect positioning of said valve element, and fluid pump means for supplying pressurized fluid for operation of the concrete pumping apparatus:

a control system comprising (A) fluid circuit means interconnecting the fluid pump means with the fluid motor means and including (1) first fluid control valve means provided with electrical actuating me'ans and connected in said fluid circuit means for controlling fluid flow to the first fluid motor means to selectively effect movement thereof in either direction, said electrical actuating means having two independently energizable electric solenoids for selective operation of said fluid control valve means, and

(2) second fluid control valve means provided with electrical actuating means and connected in said fluid circuit means for controlling fluid flow to the second fluid motor means to selectively efi'ect movement thereof in either direction, said electrical actuating means having two independently energizable electric solenoids for selective operation of said fluid control valve means, and (B) electrical control circuit means connected in circuit with the electrical actuating means of said fluid control valve means for selectively controlling the operation thereof, said electrical circuit means including (1) input terminals connectable with a source of electrical power, and (2) circuit switching means for connecting the electrical actuating means of said fluid control valve means to said input terminals for energization thereof, said circuit switching means including (a) a respective, normally open switching device connected in series with each of said electric solenoids with said switching devices closing in response to an electrical input signal for energization of a respective solenoid, (b) a first circuit portion responsive to the position of the concrete pumping piston and the movable valve element of the valve means and operative to provide a respective electrical input signal for each of said switching devices in predetermined sequence for effecting an automatic concrete pumping operation with the concrete pumping pumping unit, (c) a second circuit portion having manually operable switches to provide a respective electrical input signal for each of said switching devices independently of each other for independent operation of the concrete pumping piston and the movable valve element, and (d) switch means interconnected in circuit with said first and second circuit portions to connect either of said circuit portions to said input terminals to alternatively enable operation of either circuit portion.

5. The concrete pumping apparatus of claim 4 wherein said circuit switching means includes blocking circuit means interconnected between said first and second circuit portions to prevent interaction therebetween resulting from concurrent operation of both of said circuit portions.

6. The concrete pumping apparatus of claim 5 wherein said blocking circuit means prevent energization of the electrical actuating means of said fluid control valve means through the manually operable switches of said second circuit portion when said first circuit portion is enabled.

7. The concrete pumping apparatus of claim 4 wherein the fluid pump means includes a first fluid pump connected in said fluid circuit means for supplying fluid under pressure to only said first fluid control valve means and a second fluid pump connected in said fluid circuit means for supplying fluid under pressure to only said second fluid control valve means for independent operation of the first and second fluid motor means.

8. The concrete pumping apparatus of claim 4 having a concrete supply hopper for re'ceiving concrete in fluid form and provided with a discharge opening in communication with the inlet orifice of the valve means and which includes concrete agitating means mounted in the supply hopper and adapted to be rotatably driven for agitation of concrete within the supply hopper, fluid motor driving means connected in said fluid circuit means and mechanically connected with said agitating means and operable to rotate said agitating means in either direction, and agitator fluid control valve means connected in said fluid circuit for controlling fluid flow to said fluid motor driving means, said agitator fluid control valve means being connected in series fluid flow relationship to said second fluid control valve means.

9. The concrete pumping apparatus of claim 8 wherein the fluid pump means includes a first fluid pump connected in said fluid circuit means for supplying fluid under pressure to only said first fluid control valve means and a second fluid pump connected in said fluid circuit means for supplying fluid under pressure to only said series connected second fluid control valve means and said agitator fluid control valve means.

10. The concrete pumping apparatus of claim 4 wherein the first circuit portion of said circuit switching means includes (A) a first limit switch responsive to the position of the pumping piston and positionable in either of two positions and connected in circuit with the switching devices for the electric solenoids of said first fluid control valve means for selective energization of the electric solenoids in relation to the position of the pumping piston, and

(B) a second limit switch responsive to the position of the movable valve element and positionable in either of two positions and connected in circuit with the switching devices for the electric solenoids of said second fluid control valve means for selective energization of the electric solenoids in relation to the position of the movable valve element.

11. The concrete pumping apparatus of claim 4 wherein the first circuit portion of said circuit switching means includes (A) a first limit switch having first and second terminals and a movable contact engaging a respective one of said terminals in response to displacement of the pumping piston, said contact engaging said first terminal when the pumping piston is displaced to a position remote to the end of the pump cylinder in communication with the valve means at the completion of an intake stroke and engaging said second terminal when the pumping piston is displaced to a position adjacent to the end of the pump cylinder in communication with the valve means at the completion of a discharge stroke,

(B) signal forming circuit means connected in circuit between the first terminal of said first limit switch and one of said switching devices for said first fluid control valve means for causing displacement of the pumping piston in a discharge stroke and a gating circuit connected in circuit between the second terminal of said first limit switch and the other of said switching devices for said first fluid control valve means for causing displacement of the pumping piston in an intake stroke, said signal forming circuit means and said gating circuit forming said electrical input signal for closing the respective switching device in response to engagement of the movable limit switch contact with the respective terminal,

(C) a second limit switch having first and second terminals and a movable contact engaging a respective one of said terminals in response to displacement of the movable valve element, said contact engaging said first terminal when the valve element is psitioned in closing relationship to the outlet orifice and engaging said second terminal when the valve element is positioned in closing relationship to the inlet orifice, and

(D) a gating circuit connected in circuit between each terminal of said second limit switch and a respective one of the switching devices for said second fluid control valve means, said gating circuits forming said electrical input signal for closing the respective switching device in response to engagement of the movable limit switch contact with the respective terminal.

12. The concrete pumping apparatus of claim 11 Wherein each of said gating circuits requires; the application of a signal in addition to that provided by the respective limit switch, to form said electrical input signal, a first one of said gating circuits in circuit with said second fluid control valve means for causing the movable valve element to move into closing relationship to the inlet orifice connected to receive such additional signal from said signal forming circuit means, a second one of said gating circuits in circuit with said second fluid control valve means for causing the movable valve element to move into closing relationship to the outlet orifice connected to the second terminal of said first limit switch, and said gating circuit in circuit with said first fluid control valve means connected to said first terminal of said second limit switch thereby providing automatic cyclic operation of the pumping piston and the movable valve element in performing a pumping operation.

13. In concrete pumping apparatus having a concrete pumping unit which includes first and second concrete pump cylinders and first and second concrete pumping pistons reciprocable in respective ones of said cylinders,

first and second valve means in communication with respective ones of said pump cylinders for controlling concrete flow relative thereto, each said valve means including an inlet orifice, an outlet orifice, and a movable valve element selectively positionable to alternatively connect said pump cylinder to either of said orifices,

first fluid motor means mechanically coupled with said first pumping piston and selectively operable to effect reciprocable movement of said first pump piston,

second fluid motor means mechanically coupled with said valve element of said first valve means and selectively operable to effect positioning of said valve element,

third fluid motor means mechanically coupled with said second pumping piston and selectively operable to efiect reciprocable movement of said second pump piston, and fourth fluid motor means mechanically coupled with said valve element of said second valve means and selectively operable to effect positioning of said valve element, and fluid pump means for supplying pressurized fluid for operation of the concrete pumping apparatus:

a control system comprising (A) fluid circuit means interconnecting the fluid pump means with the fluid motor means and including (l) first, second, third and fourth fluid control valve means provided with respective electrical actuating means and connected in said fluid circuit means for controlling fluid flow to the first, second, third and fourth fluid motor means, respectively, and

(B) electrical control circuit means connected in circuit with the electrical actuating means of said fluid control valve means for selectively controlling the operation thereof, said electrical circuit means including (1) input terminals connectable with a source of electrical power, and

-(2) first circuit switching means for connecting respective electrical actuating means of said first and second fluid control valve means to said input terminals for energization thereof and second circuit switching means for connecting respective electrical actuating means of said third and fourth fluid control valve means to said input terminals for energization thereof, said first and second circuit switching means including (a) a first circuit portion responsive to the position of the respective first and second concrete pumping pistons and to the position of the movable valve elements of the respective first and second valve means and operative to energize the electrical actuating means of the respective ones of said fluid control valve means in predetermined sequence for effecting an automatic concrete pumping operation with either of the concrete pump cylinders and pumping pistons,

(b) a second circuit portion having manually operable switches to energize the electrical actuating means of each of raid fluid control valve means independmtly of each other for independent operation of the concrete pump pistons and the movable valve elements, and

(c) switch means interconnected in circuit with said first and second circuit portions to connect either of said circuit portions to said input terminals to alternatively enable operation of either circuit portion, and

(3) synchronizing circuit means interconnected between said first circuit portions of said first and second circuit switching means for maintaining out-of-phase operation of the first pumping piston and valve means relative to said second pumping pisand valve means when said first circuit portions are enabled.

14. The concrete pumping apparatus of claim 13 where in said electrical control circuit means includes respective enabling circuit means interconnected between each of said first circuit portions of said first and second circuit switching means and the second circuit portion of the other of said first and second circuit switching means to enable the one of said first circuit portions when the second circuit portion of the other of said circuit switching means is enabled.

15. The concrete pumping apparatus of claim 13 wherein said first and second circuit switching means each includes respective blocking circuit means interconnected between the first and second circuit portions thereof to prevent interaction therebetween when said first and second circuit portions are concurrently operated.

16. The concrete pumping apparatus of claim 15 wherein each of said blocking circuit means prevents energization of the electrical actuating means of the respective fluid control valve means through the manually operable switches of said second circuit portion when the respective first circuit portion is enabled.

17. The concrete pumping apparatus of claim 13 in which each concrete pump cylinder is provided with a lubrication orifice at a point which coincides with the position of the concrete pumping piston at the completion of an intake stroke and is adapted to utilize the fluid for operation of said fluid circuit means for lubrication of the pump cylinder and pumping piston, said fluid circuit means including a fluid conduit connecting with each respective lubrication orifice, said second and fourth fluid control valve means each having a fluid outlet port connected with a respective fluid conduit and which is provided with pressurized fluid when the respective control valve means is actuated to operate the second and fourth fluid motor means in positioning a respective movable 24 valve element in closing relationship to the inlet orifice of the valve means and thereby cause fluid to flow into the pump cylinder through the lubrication orifice.

18. The concrete pumping apparatus of claim 17 having a fluid flow restrictor interposed in each respective fluid conduit connecting with a lubrication orifice to limit fluid flow thereto.

19. The concrete pumping apparatus of claim 13 in which each concrete pump cylinder is provided With a lubrication orifice at a point which coincides with the position of the concrete pumping piston at the completion of an intake stroke and is adapted to utilize the fluid for operation of said fluid circuit means for lubrication of the pump cylinder and pumping piston, and wherein said fluid circuit means includes a source of pilot fluid having a minimum fluid pressure, said second and fourth fluid control valve means each includes a control valve connected in circuit with the second and fourth fluid motor means, respectively, for controlling operation thereof and provided with fluid actuation means, a pilot valve connected in circuit with said source of pilot fluid and said fluid actuation means for controlling operation of a respective control valve and provided with said electrical actuating means, each said pilot valve having a fluid outlet port connected with a fluid actuation means for actuating a respective control valve in operating the respective second or fourth fluid motor means in positioning a respective movable valve element in closing relationship to the inlet orifice of the valve means, and a fluid conduit connecting each pilot valve port with a respective cylinder lubrication orifice, each said fluid conduit having a fluid flow restrictor interposed therein to maintain pilot pressure upstream of said flow restrictor, the fluid actuation means of each control valve being connection to a respective pilot valve port upstream of said flow restrictor.

20. The concrete pumping apparatus of claim 13 wherein the fluid pump means includes a first fluid pump connected in said fluid circuit means for supplying fluid under pressure to only said first fluid control valve means, a second fluid pump connected in said fluid circuit for supplying fluid under pressure to only said third fluid control valve means, and a third fluid pump connected in said fluid circuit means for supplying fluid under pressure to said second and fourth fluid control valve means.

21. The concrete pumping apparatus of claim 13 in which each fluid motor means is of the double acting type and wherein said first, second, third and fourth fluid control valve means are each selectively operable to effect movement of the respective fluid motor in either direction, the electrical actuating means of each fluid control valve means having two independently energizable electric solenoids for selective operation of the respective fluid control valve means, and said electrical control circircuit means includes a normally open switching device connected in series with each electric solenoid of the electrical actuating means of each fluid control valve means, each switching device closing for energization of a respective solenoid in response to an electrical input signal, the first circuit portion of each of said circuit switching means being connected to the respective switching devices and operative to provide an electrical input signal to each switching device.

22. The concrete pumping apparatus of claim 21 where in each of said first circuit portions of said first and second circuit switching means includes (A) a first limit responsive to the position of the respective pumping piston and positionable in either of two positions and connected in circuit with the switching devices for the electric solenoids of each said first and third fluid control valve means, respectively, for selective energization of the electric solenoids in relation to the position of the pumping piston,

(B) a second limit switch responsive to the position of the respective movable valve element and positionable in either of two positions and connected in circuit with the switching devices for the electric solenoids of each said second and fourth fluid control valve means, respectively, for selective energization of the electric solenoids in relation to the position of the movable valve element.

23. The concrete pumping apparatus of claim 21 wherein each of said first circuit portions of said first and second circuit switching means includes (A) a first limit switch having first and second terminals and a movable contact engaging a respective one of said terminals in response to displacement of the respective pumping piston, said contact engagingrsaid first terminal when the pumping piston is displaced to a position remote to the end of the pump cylinder in communication with the valve means at the completion of an intake stroke and engaging said second terminal when the pumping piston is displacedto a position adjacent to the end of the pump cylinder in communication with the valve means at the completion of a discharge stroke,

(B) respective signal forming circuit means connected in circuit between the first terminal of said each of said first limit switches and a respective switching device for each said first and third fluid control valve means for causing displacement of the respective pumping piston in a discharge stroke and a gating circuit connected in circuit between the second terminal of said first limit switch and the other of said switching devices for each said first and third fluid control valve means for causing displacement of the respective pumping piston in an intake stroke, said'signal forming circuit means and said gating circuits forming said electrical input signal for closing the respective switching devices in response to engagementof the movable limit switch contacts with the respective terminal,

(C) a second limit switch having first and second terminals and a movable contact engaging a respective one of said terminals in response to displacement of the respective movable valve element, said contact engaging said first terminal when the valve element is positioned in closing relationship to the outlet orifice and engaging said second terminal when the valve element is positioned in closing relationship to the inlet orifice, and

(D) a gating circuit connected in circuit between each terminal of said second limit switch and" a respective one of the switching devices for said second and fourth fluid control valve means, said gating circuits forming said electrical input signal for closing the respective switching device in response to engagement of the respective movable limit switch contact with the respective terminal.

24. The concrete pumping apparatus of claim 23 wherein each of said gating circuits requires the application of a signal in addition to that provided by the respective limit switch to form said electrical input signal, a first one of said gating circuits in circuit with each said second and fourth fluid control valve means for causing the respective movable valve element to move into closing relationship to the inlet orifice connected to receive such additional signal from the respective signal forming circuit means, a second one of said gating circuits in circuit with said second and fourth fluid control valve means for causing the respective movable valve element to move into closing relationship to the outlet orifice connected to the second terminal of the respective first limit switch, and said gating circuit in circuit with each said first fluid control valve means connected to said first terminal of said second limit switch thereby providing automatic cyclic operation of the respective pumping piston and the movable valve element in performing a pumping operation.

25 The concrete pumping apparatus of claim 23 wherein each of said signal forming circuit means comprises a gating circuit requiring the application of a signal in addition to that provided by the respective first limit switch,

(A) a first gating circuit for supplying a signal having an output terminal connected to the gating circuit of one of said signal forming circuit means in one of said first circuit portions and having two input terminals, one of said input terminals connected to the first terminal of the first limit switch of the other of said first circuit portions and the other of said input terminals connected to the second circuit portion associated with said other first circuit portion to receive a signal therefrom when said second circuit portion is enabled, said first gating circuit supplying a signal when receiving a signal at either of said input terminals, and

(B) a second gating circuit for supplying a signal having an output terminal connected to the gating circuit of one of said signal forming circuit means in the other of said first circuit portions and having two input terminals, one of said input terminals connected to the first terminal of the first limit switch of said one first circuit portion and the other of said input terminals connected to the second circuit portion associated with said one first circuit portion to receive a signal therefrom when said second circuit portion is enabled, said second gating circuit supplying a signal when receiving a signal at either of said input terminals.

26. The concrete pumping apparatus of claim 25 which includes feedback circuit means connected between an 0utput of said gating circuit of each of said signal forming circuit means and interconneted terminals of said gating circuit and a respective gating circuit of said synchronizing circuit means for maintaining the output thereof so long as the respective limit switch contact engages the respective first terminal.

References Cited UNITED STATES PATENTS 3,198,123 8/1965 Wilkinson et al. 10349 3,279,382 10/1966 Bennett 103-49 3,279,383 10/1966 Smith 103-49 3,327,634 6/ 1967 Whiteman 103-49 3,380,388 4/ 1968 Sherrod 103-49 ROBERT M. WALKER, Primary Examiner US. Cl. X.R. 103-227 22 5 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3.477.380 Dated November ll, 1909 l fl Frederic R. Jonanson t} Meredith E. Smith It is certified that erro r appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 25, line 21, cancel "said".

Column 26 line 14 after "switch," insert and said synchronizing circuit means includes Signed and sealed this 6th day of July 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR'. I WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents