US3807450A - Hydraulic valve system and method - Google Patents

Hydraulic valve system and method Download PDF

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US3807450A
US3807450A US31544672A US3807450A US 3807450 A US3807450 A US 3807450A US 31544672 A US31544672 A US 31544672A US 3807450 A US3807450 A US 3807450A
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hydraulic
valve
means
connected
adapted
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R Wailes
S Ottenstein
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M and J Valve Co
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M and J Valve Co
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    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16KVALVES; TAPS; COCKS; ACTUATING-FLOATS; DEVICES FOR VENTING OR AERATING
    • F16K31/00Actuating devices; Operating means; Releasing devices
    • F16K31/12Actuating devices; Operating means; Releasing devices actuated by fluid
    • F16K31/122Actuating devices; Operating means; Releasing devices actuated by fluid the fluid acting on a piston
    • F16K31/124Actuating devices; Operating means; Releasing devices actuated by fluid the fluid acting on a piston servo actuated
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10TTECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T137/00Fluid handling
    • Y10T137/8593Systems
    • Y10T137/877With flow control means for branched passages
    • Y10T137/87708With common valve operator
    • Y10T137/87764Having fluid actuator
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10TTECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T137/00Fluid handling
    • Y10T137/8593Systems
    • Y10T137/877With flow control means for branched passages
    • Y10T137/87708With common valve operator
    • Y10T137/87772With electrical actuation

Abstract

A hydraulic valve operating system having a plurality of main flow control valves, each provided with a hydraulic power operator, together with means including control valves (e.g., four-way valves) connected to receive liquid from a common pressure accumulator. Selective operation of the control valves is effected by electrical means including circuitry having a common conductor through which current flows when the operation of any one of the control valves is initiated. An isolation valve is interposed in the hydraulic connection to the hydraulic means. An electrical sensing means is provided and is connected with the isolation valve so that when the electrical circuitry is selectively operated for the purpose of operating any one of the control valves, the isolation valve is operated whereby liquid under pressure is supplied for the required operation. Thus during standby periods no loss of liquid from the accumulator occurs by way of leakage of the control valves. Also, the method of operation of such a system.

Description

United States Patent [191 Wailes et al.

[ Apr. 30, 1974 HYDRAULIC VALVE SYSTEM AND METHOD 1 [75] lnventorsz. Rodney A. Wailes, Houston; Sidney Allan Ottenstein, Spring, both of Tex.

[73] Assignee: M & J Valve Company, Houston,

Tex.

[22] Filed: Dec. 15, 1972 [21 Appl. No.: 315,446

[52] US. Cl. 137/608 [5]] Int. Cl. Fl6k 11/00 [58] Field of Search..... 137/625.48, 625.49, 625.41, l37/625.47, 608

[56] References Cited UNITED STATES PATENTS 3,580,282 5/1971 Van Arsdale et al 137/608 3,437,098 4/1969 Stark et a]. 137/609 x 3,523,675 8/1970 Grove et al. 251/94 3,636,977 1/1972 Adams 137/608 3,682,575 8/1972 Guddal et al. l37/625.48 x 3,708,047 1 1973 Kuhnle et al. 137/608 X Primary Examinerl-lenry T. Klinksiek [57] ABSTRACT A hydraulic valve operating system having a plurality of main flow control valves, each provided with a hydraulic power operator, together with means including control valves (e.g., four-way valves) connected to receive liquid from a common pressure accumulator. Selective operation of the control valves is effected by electrical means including circuitry having a common conductor through whichcurrent flows when the operation of any one of the control valves is initiated. An isolation valve is interposed in the hydraulic connection to the hydraulic means. An electrical sensing means is provided and is connected with the isolation valve so that when the electrical circuitry is selectively operated for the purpose of operating any one of the control valves, the isolation valve is operated whereby liquid under pressure is supplied for the required operation. Thus during standby periods no loss of liquid from the accumulator occurs by way of leakage of the control valves.

Also, the method of operation of such a system.

4 Claims, 2 Drawing Figures 1 HYDRAULIC VALVE SYSTEM AND METHOD BACKGROUND OF THE INVENTION common system and arranged whereby openingand closing of the valves can be controlled from a central station. Particular examples are valves used for tank farms, meter provers,-pumping stations and the like. One system of this kind makes use of hydraulic operators mounted upon each of the valves, together with means for supplying each of the operators with hydraulic liquid under pressure from a common source. The application of liquid to each operator is controlled by a control valve, as for example one of the four-way type,the setting of which serves to supply liquid under pressure to one or the other of' the pressure chambers of the operator, with the liquid in the other chamber being exhausted. When the source of hydraulic liquid under pressure is a continuously operating pump, such a system operates satisfactorily irrespective of some leakage which may occur through the four-way control valves. However it is frequently desirable to 'use a socalledpressure accumulator as a source of hydraulic liquid, instead of a continuously operating pump. The accumulator is generally connected to a pressure pump, the driving motor of which is controlled by a pressure responsive switch. Thus the motor is operated to drive the pump only when the pressure in the accumulator falls below a predetermined value. With such an arrangement leakage causes difficulty, because it necessarily requires frequent operation of the pump to maintain the desired pressure level.

SUMMARY AND OBJECTS OF THE INVENTION In general it is an object of the present invention to provide a hydraulic valve operating system and method which makes use of an accumulator as a source of liquid under pressure, but which prevents loss of pressure from the accumulator when no command is being applied to cause operation of one of the control valves.

Another object of the invention is to provide a system and method which makes use of reliable means for indicating when a command is being applied for effecting operation of a valve, and for substantially instantly conmeeting the accumulator to the manifold of the hydraulic means associated with all of the valves, for carrying out a cycle of operation.

Another object is to provide reliable and sensitive detecting means associated with the electrical circuitry of the system, and which is employed to effect hydraulic communication between the accumulator and the hydraulic means associated with all of the valves.

In general, the present invention makes use of a plurality of main flow control valves each of which is provided with a hydraulic'operator adapted to be energized to carry out valve opening and closing operations. A hydraulic accumulator is used as the source of hydraulic liquid under pressure. Also a control valve, as for example one of the four-way type, is associated with the operator of each of the main valves, and is adapted to be set into operating positions to effect valve opening and closing operations. Fluid connections are pro- 2 vided between each control valve and a common hydraulic manifold line. Solenoid means are provided which are adapted to be electrically energized, and which are associated with the control valves in such a manner as to effect their conditioning for application of hydraulic liquid under pressure to the valve operators. Electrical circuitry connects with the solenoid means, and the circuitry includes control switches adapted to be selectively operated for selectively energizing any one of the solenoid means whereby a particularmain valve is opened or closed. The circuitry includes one common conductor which is connected to one side of a means provided for forming a fluid connection between the hydraulic accumulator and the common manifold, and interposed in this connection there is a normally closed isolation valve. Means is provided which serves to open this isolation valve immediately in response to operation of any one of the control switches.

Additional objects and features of the invention will appear from the following description in which the preferred embodiment of the invention has been set forth in detail in conjunction with the accompanying drawmgs.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram illustrating a hydraulic system incorporating the present invention.

FIG. 2-is a circuit diagram illustrating the electronic means employed in FIG. 1 for detecting the closing of any one of the control switches.

' DESCRIPTION OF THE PREFERRED EMBODIMENT The system shown in FIG. 1 consists of a plurality of main valves A, B and C, which in this instance are of the gate type and which are adapted to be power operated. Each of the power operators 10 for these valves may be a double-acting cylinder-piston assembly having the piston oroperating rod directly connected to the gate of the valve. During poweroperation hydraulic liquid under pressure is supplied to one end of the cylinder and liquid is exhausted from the other end. In some instances the' valves may be of the rotary ball type, in which event the operator may be of the rotary vane type and operated in substantially the same manner.

A single source of hydraulic liquid under pressure is provided for the operation of all of the valves. The means employed,'indicated generally at 11, includes a hydraulic accumulator 12 which is connected to the discharge side of the pump 13, through valve 14. This pump has its suction side connected to the liquid reservoir 16, and is controlled in such a manner as to maintain a desired pressure within the accumulator. Thus the pump is shown driven by an electric motor 17, which in turn is energized by the electrical circuit 18. The The circuit includes the pressure switch 19, having a pressure connection to the accumulator 12. When the accumulator pressure falls below a predetermined level, the switch 19 is closed to energize the motor 17, thus returning the pressure to the desired value.

As is well known to-those familiar with hydraulic equipment, the accumulator 12 may consist of a pressure vessel having its interior divided into two chambers by a flexible diaphragm. One chamber is sealed and contains gas while liquid is introduced and withdrawn from the other chamber. As the quantity of liquid increases the gas pressure increases until the desired pressure level is attained. The capacity required for the accumulator 12 depends upon the requirements of the system. Assuming that only one of the main valves is to be operated at a time, then the accumulator should have sufi'tcient capacity to effect a cycle of operations of one valve without serious drop in hydraulic pressure. In instances where two or more valves may be operated simultaneously, the capacity of the accumulator must be increased accordingly. The pump 13 is operated automatically as occasion requires, to maintain the desired pressure level in the accumulator. Valve controlled line 20 may be provided for bypassing liquid to the reservoir 16.

Parts of a hydraulic system such as disclosed in U.S. Pat. No. 3,523,675 are associated with each of the hydraulic operators 10 of the main valve. Thus the hydraulic connections 21 and 22 to the ends of each operator cylinder make connection with the four-way control valve 23, through the check valve assembly 24. The purpose of the check valve assembly is to provide a hydraulic lock which is effective after the end of each cycle of operation.

Each of the four-way control valves 24 is shown having connections with a hydraulic manifold pressure line 26, and a hydraulic exhaust line 27. The pressure line 26 is shown connected by line 28 with the accumulator 12. The exhaust line 27 is shown connected to return exhaust liquid to the reservoir 16.

The arrangement is such that for one operating position of the operating member of each four-way control valve 23, liquid under pressure is supplied through line 21 to operator l and exhausted through line 22, thereby closing the associated main valve. Conversely, when the control valve 23 is placed in its other operating position, liquid under pressure is supplied through line 22 and exhausted through line 21, to open the main valve.

Various types of motive devices can be used for moving the operating member of each control valve 23 from one operating position to the other. For example, in some instances the motive'device may be an electrical solenoid, or it may be a pneumatic pressure operated device. In the system illustrated each device 26, indicated as connected to the operating member of the associated control valve 23, is a pneumatic motive device of the cylinder-piston type. Application of pneumatic pressure, indicated as being supplied through line 27, is shown being controlled by the solenoid valves 29 and 30. These valves are connected to electrical circuitry whereby they are selectively operated. Normally these valves are closed, but when electrically energized, pneumatic pressure is applied to one end or the other of the cylinder of device 26. When de-energized the connection to the device 26 is vented to the atmosphere as indicated. It will be evident that when one solenoid is energized, the associated control valve 23 is conditioned to cause hydraulic pressure to be supplied to the operator for one cycle of operation, as for example to open the valve. When the other solenoid is energized the cycle of operation serves to close the valve.

The location of the parts just described, namely the check valve assembly 24, the four-way control valve 23, the motive device 26, and the solenoid valves 29 and 30, may vary in accordance with requirements.

Generally it is desirable to locate the check valve assembly 24 near the hydraulic operator 10. However, the four-way control valves 23, the motive devices 26, and the solenoid valves 29 and 30, may be located at a remote operating station.

The electrical circuitry connected to the solenoid valves 28 and 29 includes a source of current represented by the current supply lines L1 and L2. It also includes the selectively operable switches 51A, 82A, SIB, S2B, SlC and S2C. When these switches are closed, the solenoid valve 29 or 30 of the corresponding main valve is energized. In other words, the selective operation of the switches serves to initiate a desired cycle of operation of each one of the main valves A, B or C. The circuitry also includes a so-called trigger circuit 31, which connects to the common conductor 32 of the circuitry. This conductor connects to one side of all of the solenoid operated valves. The trigger circuit 31 is shown having connections across the lines L1 and L2, and is also shown connected by circuit 33 with the relay switch 34. The contacts of the relay switch 34 control circuit 36, which serves to energize the winding of the solenoid isolation valve 37. The source of energizing current for circuit 36 may likewise be the lines L1 and L2.

The valve 37 is normally biased toward closed position. It is inserted into the line 28 leading to the accumulator 12. It may be bypassed by valve 38 to permit manual or emergency operation.

In general the purpose of the trigger circuit 31 is to detect current flow in line 32, which indicates that one of the selectively operated switches is being operated to effect a cycle of operation of one of the valves. When the trigger circuit detects current flow in the return line 32, it causes current to be applied to the relay switch 34, thus energizing the winding of solenoid valve 37 to open the same and thereby causing hydraulic pressure to be applied to the manifold line 26 of the hydraulic system. Immediately after completing a cycle of operation, the control switch is opened. whereby current flow in line 32 is discontinued. Under such conditions the trigger circuit de-energizes the relay switch 34, thus de-energizing the winding of the solenoid valve 37. Closure of this valve, and the maintenance of this valve in closed condition under standby conditions prevents any possible leakage of hydraulic liquid through the line 28 into the pressure line 26 of the system.

FIG. 2 illustrates a desirable type of trigger circuit. It consists of diode 1 connected between the conductor 32 and line L2, and the series connected diodes 2, 3, 4 and 5, likewise connected across conductor 32 and line L2. There is also a diode 6 provided with a control connection 41, which connects with the conductor 32 through the resistor 42. One side of the diode 6 connects with line L2, and the other side connects with one side of the coil of relay switch 34, through the conductor 43. The other side of the coil of relay switch 34 is connected by conductor 44 to line L1, through the resistor 46. A condensor 47 connects to conductors 43 and 44, and is therefore shunted across the coil of relay switch 34.

The components of the trigger circuit shown in FIG. 2 should be selected in accordance with requirements, and the voltage of lines L1 and L2. Assuming that lines L1 d L2 spr ss 1. X9 e tsrae nsputre t t components can be as follows: Diode 1, IN4997; each of diodes 2, 3, 4 and 5, IN4997; diode 6, 2N3670; resistor 42, 47 ohms; resistor 46, 600 ohms; and condensor 47,50 mfd. 'Iihe above numbers refer to standard man ufacturers specifications for solid state diodes.

Operation of the trigger circuit described above is as follows: When a solenoid 29 or 30 is energized by operating one of the control switches, alternating current flows through the diode l for that half of the cycle when L1 is negative with respect to L2. For the other half cycle, when L1 is positive with respect to L2, current flow occurs through the series connected diodes 2-5. The voltage developed across the series connected diodes 2-5 provides trigger power through resistor 42 and connection 41, causing the diode 6 to fire each half-cycle of the alternating current. DC voltage is developed across the condensor 47, the magnitude of which can be controlled by the scaling resistor 46. This voltage suffices to actuate the relay 34, and this relay in turn causes the winding of the isolation valve 37 to be energized. The trigger circuit is immediately re stored when current ceases to flow through the common conductor 32.

The system and method described above has a number of advantages over prior hydraulic systems for the selective operation of main valves. As previously mentioned, it is difficult to prevent leakage past the several control valves 23 of such a system, and the cummulative effect of this leakage causes more or less continuous leakage flow of hydraulic liquid from the supply source. When this supply source is an accumulator, eitcessive demands are made upon the pump and associated parts which are provided for maintaining the desired pressure level in the accumulator. With the system and method described above the only possible leakage during standby is through'the isolation valve 37, and this valve can be made in such a manner that leakage is minimal. As a result, the desired pressure level can be maintained in the accumulator with minimum operation of the pressure pump 13.

We claim:

1. In a hydraulic valve system, a plurality of main flow control valves each provided with a hydraulic power operator adapted to be energized to carry out a valve operating cycle, means including a hydraulic accumulator for supplying hydraulic liquid under pressure, a control valve for the hydraulic operator of each of the main valves, means forming fluid connections between each control valve and the corresponding operator, means forming fluid connections between each control valve and a common manifold adapted to receive hydraulic liquid under pressure, solenoid means adapted to be electrically. energized and associated with each control valve to effect conditioning of the control valve whereby application of hydraulic liquid under pressure to the corresponding operator causes an operating cycle of the main valve, electrical circuitry connected to said solenoids, said circuitry including control switches adapted to be selectively operated for energizing any one of said solenoids, current supply lines connected to the circuitry, the circuitry having one conductor connected to one side of all of the solenoids and also connected to one of said current supply lines, the other one of the current supply lines being connected to one sideof the control switches, means forming a hydraulic fluid connection between the hydraulic accumulator and said common manifold, a normally closed isolation valve interposed in said lastnamed connecting means, said isolation valve being adapted to be actuated 'to open thesame, and means serving to actuate said isolation valve to open the same in response to operation of any one of said switches.

2. A system as in claim 1 in which said isolation valve is adapted to be electrically operated to open the same, and electronic means incorporated in the electrical circuitry for detecting the operation of one of said switches and for actuating said isolation valve. Whereby said isolation valve is opened responsive to operation of said switch.

3. A system as in claim 2 in which said detecting means comprises an electronic trigger circuit.

4. A method for the operation of a plurality of valves, the method making use of a plurality of main flow control valves each provided with a hydraulic power operator adapted to be energized to carry out a valve operating cycle, means including a hydraulic accumulator for supplying hydraulic liquid under pressure, a control valve forthe hydraulic operator of each of the main valves, means forming hydraulic fluid connections between each control valve and the corresponding operator, means forming hydraulic fluid connections between each control valve and a common manifold adapted to receive hydraulic liquid under pressure, solenoid means adapted to be electrically energized and associated with each control valve to effect conditioning of the control valve whereby application of hydraulic liquid under pressure to the corresponding operator causes an operating cycle of the main valve, and electrical circuitry connected to said solenoids, said circuitry including control switches adapted to be selectively operated for energizing any one of said solenoids and a source of current supply, the circuitry having one common conductor connected to one side of all of the solenoids and also connected to one of said current supply lines, the other one ofthe current supply lines being connected to one side of the control switches; the method comprising interrupting communication between the accumulator and said common manifold during standby periods, detecting flow of current in said common conductor, and establishing communication between said accumulator and said manifold line re-' sponsive to such current flow, such communication

Claims (4)

1. In a hydraulic valve system, a plurality of main flow control valves each provided with a hydraulic power operator adapted to be energized to carry out a valve operating cycle, means including a hydraulic accumulator for supplying hydraulic liquid under pressure, a control valve for the hydraulic operator of each of the main valves, means forming fluid connections between each control valve and the corresponding operator, means forming fluid connections between each control valve and a common manifold adapted to receive hydraulic liquid under pressure, solenoid means adapted to be electrically energized and associated with each control valve to effect conditioning of the control valve whereby application of hydraulic liquid under pressure to the corresponding operator causes an operating cycle of the main valve, electrical circuitry connected to said solenoids, said circuitry including control switches adapted to be selectively operated for energizing any one of said solenoids, current supply lines connected to the circuitry, the circuitry having one conductor connected to one side of all of the solenoids and also connected to one of said current supply lines, the other one of the current supply lines being connected to one side of the control switches, means forming a hydraulic fluid connection between the hydraulic accumulator and said common manifold, a normally closed isolation valve interposed in said last-named connecting means, said isolation valve being adapted to be actuated to open the same, and means serving to actuate said isolation valve to open the same in response to operation of any one of said switches.
2. A system as in claim 1 in which said isolation valve is adapted to be electrically operated to open the same, and electronic means incorporated in the electrical circuitry for detecting the operation of one of said switches and for actuating said isolation valve. Whereby said isolation valve is opened responsive to operation of said switch.
3. A system as in claim 2 in which said detecting means comprises an electronic trigger circuit.
4. A method for the operation of a plurality of valves, the method making use of a plurality of main flow control valves each provided with a hydraulic power operator adapted to be energized to carry out a valve operating cycle, means including a hydraulic accumulator for supplying hydraulic liquid under pressure, a control valve for the hydraulic operator of each of the main valves, means forming hydraulic fluid connections between each control valve and the corresponding operator, means forming hydraulic fluid connections between each control valve and a common manifold adapted to receive hydraulic liquid under pressure, solenoid means adapted to be electrically energized and associated with each control valve to effect conditIoning of the control valve whereby application of hydraulic liquid under pressure to the corresponding operator causes an operating cycle of the main valve, and electrical circuitry connected to said solenoids, said circuitry including control switches adapted to be selectively operated for energizing any one of said solenoids and a source of current supply, the circuitry having one common conductor connected to one side of all of the solenoids and also connected to one of said current supply lines, the other one of the current supply lines being connected to one side of the control switches; the method comprising interrupting communication between the accumulator and said common manifold during standby periods, detecting flow of current in said common conductor, and establishing communication between said accumulator and said manifold line responsive to such current flow, such communication being continued until such current flow is interrupted.
US31544672 1972-12-15 1972-12-15 Hydraulic valve system and method Expired - Lifetime US3807450A (en)

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US31544672 US3807450A (en) 1972-12-15 1972-12-15 Hydraulic valve system and method

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Application Number Priority Date Filing Date Title
US31544672 US3807450A (en) 1972-12-15 1972-12-15 Hydraulic valve system and method
CA187,499A CA990177A (en) 1972-12-15 1973-12-06 Hydraulic valve system and method
GB5683373A GB1418226A (en) 1972-12-15 1973-12-07 Hydraulic valve system and method
JP14025273A JPS5225570B2 (en) 1972-12-15 1973-12-15
IT3225573Q IT1002340B (en) 1972-12-15 1973-12-27 Hydraulic system valves and meto do to control

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US (1) US3807450A (en)
JP (1) JPS5225570B2 (en)
CA (1) CA990177A (en)
GB (1) GB1418226A (en)
IT (1) IT1002340B (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109458352A (en) * 2018-10-30 2019-03-12 浙江水利水电学院 A kind of Centrifugal Pump regulating device and its manufacturing method

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3437098A (en) * 1965-10-25 1969-04-08 North American Utility Constru System of automatic controls for gas mixing
US3523675A (en) * 1967-12-18 1970-08-11 M & J Valve Co Valve operating apparatus with locking means
US3580282A (en) * 1968-10-24 1971-05-25 M & J Valve Co Valve-operating system
US3636977A (en) * 1970-03-04 1972-01-25 Abex Corp Electrohydraulic flow control circuit
US3682575A (en) * 1970-12-10 1972-08-08 Karl Guddal Concrete pump
US3708047A (en) * 1970-01-20 1973-01-02 Zahnradfabrik Friedrichshafen Electro-hydraulic selector for the control of multiple loads

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3437098A (en) * 1965-10-25 1969-04-08 North American Utility Constru System of automatic controls for gas mixing
US3523675A (en) * 1967-12-18 1970-08-11 M & J Valve Co Valve operating apparatus with locking means
US3580282A (en) * 1968-10-24 1971-05-25 M & J Valve Co Valve-operating system
US3708047A (en) * 1970-01-20 1973-01-02 Zahnradfabrik Friedrichshafen Electro-hydraulic selector for the control of multiple loads
US3636977A (en) * 1970-03-04 1972-01-25 Abex Corp Electrohydraulic flow control circuit
US3682575A (en) * 1970-12-10 1972-08-08 Karl Guddal Concrete pump

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109458352A (en) * 2018-10-30 2019-03-12 浙江水利水电学院 A kind of Centrifugal Pump regulating device and its manufacturing method

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GB1418226A (en) 1975-12-17
CA990177A1 (en)
JPS5225570B2 (en) 1977-07-08
JPS4996313A (en) 1974-09-12
IT1002340B (en) 1976-05-20
CA990177A (en) 1976-06-01

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