US3223068A - Warning systems - Google Patents

Description

Dec. 14, 1965 R. l.. VAN WINKLE 3,223,068

WARNING SYSTEMS Filed DSC. 26, 1962 4 Sheets-Sheet l INVENTOR. ROY L. VAN WNKLE jj A@ Q//M/rv ATTORNEY Dec. 14, 1965 R. L. VAN WINKLE 3,223,068

. WARNING SYSTEMS Filed Dec. 26, 1962 4 Sheets-Sheet 2 TRANSMITTER Z6 #5 Ps1 /0 26 Z `SIGNAL SERVO GAGE ADJUSTABLE 44 3MP-ACTING RLLAV- DIRECT q) A:

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5 Lil 7 HORN Z ZO P51' B AIR BOOSTER 50 sIIUTTLL 56J 38 RELAY VALVE GAGE r REGULATOR ADJUSTABLE 60 40 SNAP-ACTING RELAY- RLVLRSF. i251 6 A: n -*p 38 RIG AIR SUPPLY y LJ I T. L o psr I 3-I5Psx 26 1 M; 26

AIR il 36 SIGNAL SLRVO TRANSMITTLR @lijf 2.

INVENTOR. ROY L. VAN WINKLE.

Dec. 14, 1965 R. l.. VAN wlNKLE WARNING SYSTEMS 4 Sheets-Sheet 3 Filed Dec. 26, 1962 INVENTOR. ROY L. VAN WINKLE ATTORNEY Dec. 14, 1965 R. l.. vAN wlNKLE 3,223,068

WARNING SYSTEMS Filed Dec. 26, 1962 4 Sheets-Sheet 4 w www@ INVENTOR. ROY L. VAN WINKLE /J/m, QM/WWW ATTORNEY United States Patent O 3,223,068 WARNING SYSTEMS Roy L. Van Winkle, Edmond, Okla., assigner to The Geolograph Company, Oklahoma City, kla., a corporation of Oklahoma Filed Dec. 26, 1962, Ser. No. 247,142 2 Claims. (Cl. 116-65) This invention relates generally -to pneumatic warning systems adapted to operate in conjunction with recording or indicating apparatus. More specifically, it relates to adjustable pneumatic warning systems that may be set to provide a warning at desired values of a measured variable.

In the past, it has been possible to obtain Warning systems for pneumatic apparatus that will provide satisfactory service provided that the system can be pre-set at a given value and provided, further, that it does not require subsequent adjustment or frequent changes of the value at which the warning is to be sounded. Perhaps the greatest diiculty encountered has been the development of a warning system of sucient simplicity that it can be adjusted to a certain value of a measured variable and then changed, by a relatively unskilled person, to provide a warning at a different, but desired value of the measured variable.

It is, therefore, one object of this invention to provide an improved warning system for use with pneumatic apparatus wherein the system can be easily adjusted to a pre-selected value of a measured variable.

Another object of this invention is to provide an irnproved warning system that can be easily adjusted and will sound an alarm either upon an increase above or decrease below a pre-selected value of a measured variable.

A further object of this invention is to provide an improved warning system that can be easily adjusted and will sound an alarm both upon an increase above and a decrease below the pre-selected value of a measured variable.

Generally, this invention contemplates a warning system that includes warning means, adjustable means for controlling the value at which the warning means will be actuated, and control means adapted to produce a visual indication of the value at which the adjustable means will actuate.

Other, further, and additional objects and advantages of the invention will become more apparent when the following description is read in conjunction with the accompanying drawing wherein like reference characters denote like parts in all view and wherein:

FIGURE 1 is a schematic diagram illustrating a double or dual warning system constructed in accordance with the present invention. The warning system is connected with pneumatic recording apparatus and is adapted to provide, in one circuit, an alarm above a certain Value and, in the other circuit, an alarm below a certain value.

FIGURE 2 is a schematic diagram illustrating an alternative form of the warning system of FIGURE 1.

FIGURE 3 is a schematic diagram illustrating a single warning system, also constructed in accordance with this invention, connected with a pneumatic recording apparatius and adapted to provide an alarm either above or below a certain value of a measured variable.

FIGURE 4 is a schematic diagram illustrating a single warning system constructed in accordance with the invention, connected with a pneumatic recording apparatus and adapted to provide an alarm above a certain value and below a certain value of a measured variable.

Referring to the drawings in detail, FGURE 1 shows a pneumatic transmitter connected by a conduit 28 to "ice a recording servo mechanism 12. The transmitter is also connected by a conduit to a source of air which is regulated to 20 p.s.i. in a conventional manner (not shown per se) as indicated by the reference numeral 26, the latter numeral also lbeing employed throughout this application to designate a 20 p.s.i. source of air pressure wherever required. The transmitter is also connected by means of element 11 to a variable whose condition is to be measured by the servo 12 and whose maximum or minimum condition is to be indicated by the warning system described herein. For example, the element 11 could be an arm connecting with a oat (not shown) resting on the surface of drilling mud (not shown) in a mud pit (not shown). In such an instance, the transmitter 10 would have therein a rotatable element movable in response to the pivoting motion of the element 11 and would be adapted to produce an output pressure varying between 3 and 15 p.s.i., depending upon the level in the mud pit. (A Foxboro type C.P. Position Transmitter of the type disclosed in Foxboro Catalog 14-132 of June 1958, or a Moore model 70 Motion Transmitter, such as shown on page 28 of the Moore Products Catalog, eighth edition, 1962, are suitable as pit level transmitters.)

Various other types of transmitters can be utilized, the exact type depending upon the variable to be measured. One requirement, however, for the transmitter to be used in the warning system disclosed herein is that the transmitter 10 should have an output pneumatic pressure variable between 3 and 15 p.s.i. which is a function of the measured variable.

The recording servo mechanism 12 will, of course, be compatible with the particular type of transmitter 10 employed. Brieily stated, however, a 20 p.s.i. reference pressure is introduced to the servo 12 from the source 26 referred to above. The variable signal between 3 and l5 p.s.i. is also introduced to the servo 12 through the conduit 28. The internal details of the servo are such that the indicating portion thereof will be moved to a position dependent upon the value of the variable input signal through the conduit 28. (A suitable servo has been found to be a Taylor Servomatic Motor, Series as illustrated in catalog 4B20l, issue 2, of the Taylor Instrument Company TP-618.)

The transmitter 10 is also connected by means of conduit 29 to an adjustable snap-acting relay 14 of the type disclosed in Minneapolis-Honeywell Regulator Company bulletin -2554 published lune 7, 1960. Relay 14 is a direct-acting relay as will hereinafter appear. Relay 14 is provided with an integral calibrated indicating portion 13 and an external adjusting knob 15. A pointer 17 which is slidable along the indicating portion 13 is moved by rotation of the adjusting knob 15. The relay 14 connects by means of conduit 30 to an alarm 16 (indicated asa horn).

Relay 14 is connected by means of a conduit 32 with the main air supply (for the rig) generally designated by the reference character 38. The conduit 32 also connects the relay 14 with another snap-acting relay 20, which is essentially the same as the relay 14, but is reverse-acting as will hereinafter appear. Relay 20 has an integral calibrated indicating portion 19, an external adjusting knob 21 and a pointer 23 which is movable across the calibrated portion 19 in response to rotation of the knob 21. Relay 20 connects with an alarm 18 (indicated as a horn).

A transmitter 24, which will be generally the same as the transmitter 10, is connected by means of a conduit 36 to a servo 22 which is essentially the same as the servo 12. The transmitter 24 also connects with the relay 20 by means of a conduit 37. The servo 22 and the transmitter 24 are each connected to the 20 p.s.i. reference pressure as indicated by the reference characters 26, 26.A

The transmitter 24 is connected by means of element 2S (in a manner similar to element 11) to a variable whose condition is to be measured by the servo 22.

Operation of FIGURE 1 As indicated above, the relay 14 is a `direct-acting relay, which means that this relay will be energized or opened when the pressure in the conduit 29 exceeds a predetermined value; below this pressure, the` relay 14 will remain closed. Contrariwise, the relay 20 is a reverse-acting relay in that it will not be energized or opened until the pressure in the conduit 37 drops below a predetermined value; above this predetermined value, the relay 20 will remain closed. It Will be now assumed that the element 11 on the transmitter 10 is a float arm connecting with a float (not shown) resting on the surface of the drilling mud in the mud pit which is on the suction side of the mud pump. It is well recognized that it is generally desirable to know when the mud level in the suction pit drops below a certain level so as to alert the crew to the possibility of a lost-circulation problem. It will be further assumed that the element 25 is a float arm connected to a float (not shown) resting on the surface of the drilling mud in the mud pit on the discharge or recovery side of the mud pumping system. It is also generally recog nized that it is desirable to know when the level of the mud in the discharge pit rises above a certain predetermined level to alert the crew to the possibility of a blowout. One further point should be mentioned, and that is, that the transmitters and 24 will keach show an increase in output signal pressure when the level in the respective mud pit drops.

With the system of FIGURE 1 being connected in the manner shown and consistent with the above assumptions, if the level in the suction pit drops below a predetermined value, the signal in the conduit 29 vfrom the transmitter 10 will increase so as to open or energize the relay 14. Opening the relay 14 will permit the air from the rig air supply 38 to pass through the conduit 32, the relay 14 and the conduit 30 to the alarm 16 so as to sound the latter. Thereafter, as the level again rises in the suction pit, the relay y14 will close when the pressure in the conduit 29 drops below the actuation .pressure or, otherwise stated, when the level in the suction pit rises above the desired level.

If the level of the drilling mud in the discharge mud pit should rise above the predetermined desired level, the pressure in -the conduit 37 from the transmitter 24 will decrease so as to actuate or open the relay permitting air to pass therethrough from the rig air supply 38 and the conduit 32 and through the conduit 34 to the alarm 18, thereby sounding the same. The relay 20 will remain open until the pressure in the conduit 37 rises above the actuation pressure or, stated differently, when the level in the discharge.. pitY drops below the predetermined level.

Whereas, the operation of FIGURE 1 has been described, purely ror purposes of example, in connection with a mud pumping system and the mud pits used in connection therewith, it should be obvious that the system of FIGURE 1 could be employed in connection with any other system having two variables, one of which should not fall below a certain predetermined value and the other of which should not exceed a certain predetermined value. Naturally, the form of the transmitter 10 might vary, depending upon the particular variable involved and the manner in which the same was measured. At any event, the transmitters 10 and 24 will be such as to produce a 3 to 15 p.s.i. output signal variable over this range, depending upon the value of the measured variable at any given instant.

FIGURE 2 is similar to FIGURE 1 in that two variables are being measured simultaneously and that a warning system is provided for the variables; however, instead of providing two alarms, only one alarm 16 is shown in FIG. 2. vThe relays ,14a andava shown in FIGURE 2 ,are

similar to relays 14 and 20, respectively, in FIGURE 1, except that those of FIGURE 2 are simplified to the extent that no externally calibrated portions are provided on these relays. At this juncture, it might be mentioned that the relays 14 and 20 can have their graduations marked to correspond, for example, with given level conditions for the two mud pits whose levels are sensed by the transmiters' 10 and 24, respectively. In such an instance, if it is desired to change from one given reference level in a particular mud pit, then the knob 15 or 21 can be adjusted so that the pointer 17 or 23 is opposite the desired level.

Returning to a consideration of FIGURE 2, a calibration of the relays 14a and 20a is elected by means of the selector valves 40 and 42 and the gages 44 and 46 as described below. The transmitter 10 is connected to the servo 12, as before, by the conduit 28 and by conduit 43 to a selector valve 42. A conduit 58 connects the selector valve 42 to a gage 44 and the relay 14a. Transmitter 10, the servo 12 and the relay 14a are all connected to a 20 p.s.i. source of air as indicated by the common reference numeral 26 as shown. The relay 14a connects by means of conduit 52 with a shuttle valve 48, the latter being essentially a two-way check valve. Shuttle valve 48 connects to a booster relay 50, which in turn is connected by conduit 30a to the alarm 16. The rig air supply 38 also connects with the booster relay S0.

If it is desired to operate the alarm 18 solely by the output from the shuttle valve 48, the booster relay 50 Will be unnecessary; however, its use will produce a stronger or louder signal. Transmitter 24 is connected by means of conduit 36 to servo 22, and by means of conduit 41 to a :selector valve 40. The selector valve 40 connects by means of conduit 60 with a gage 46 and relay 26a, which, in turn, connects by means of conduit 54 with the opposite side of the shuttle valve 48 (opposite with respect to conduit 52). Relay 20a, servo 22, and transmitter 24 are all connected to a 20 p.s.i. source of air as designated by the common reference character 26. The two selector valves 40 and 42 are connected to each other and to an adjustable regulator 62 by means of the conduit 56. Regulator 62 is, in turn, connected with the air supply 38 as shown.

Operation of FIGURE 2 When the circuit of FIGURE 2 is in its operating position, the sequence of operations described above with respect to FIGURE 1 will apply, except that only one alarm 16 is employed. However, the shutle valve 48 is such that when the relay 14a is opened or energized, pressure will be transmitted through the relay 14a and the conduit 52 to the shuttle valve. The pressure in the conduit 52 will move the shuttle valve in such a manner as to prevent pressure being transmitted through the valve into the conduit S4. Thus, the pressure transmitted to the shuttle valve 48 Will pass through the booster relay 50 and conduit 30a to the alarm 16 or, more precisely, actuation of the booster relay 50 as thek result of the pressure transmitted to it from the shuttle valve 48 will permit passage of air from the rig air supply 38 through the booster relay 50 to the conduit 30a and to the alarm 16. Conversely, when the relay 20a is actuated or opened, pressure in the conduit 54 will move the internal mechanism (not shown) of the shuttle valve in the opposite direction to prevent communication with the conduit 52. Thus, pressure passes from the shuttle valve 48 in the same manner to the booster relay 50 so as t0 actuate the alarm 16.

The selector valves 40 and 42, gages 44 and 46 and adjustable regulator 62 are provided for the purpose of Calibrating the relays 14a and 20a. The dials on the gages 44 and 46 are calibrated in advance to correspond with the units of measurement of the measured variables (not shown) which operate the transmitters 10 and 24, respectively. Thus, if transmitters 10 and 24 are used in a mud pumping system, for example, as described above in connection with FIGURE 1, then gages 44 and 46 will be calibrated in units of liquid level. Valve 42, for example, is movable into two positions to permit flow in two directions indicated by the right-angled arrows designated by the reference characters A and B, of course, at separate periods of time. Selector Valve 40 is also movable so as to permit the two different flow conditions indicated by the right-angled arrows designated by the reference characters A and B.

Now, if it is desired to calibrate relay 14a, selector Valve 40 is placed in a flow condition corresponding to arrow A and selector valve 42 is moved to a flow condition corresponding to arrow B. Thereafter, the control on adjustable regulator 62 is adjusted until the pressure reading on the gage 44 corresponds to the desired Value (or level) of the variable whose condition is sensed by the transmitter 10. When the gage 44 is brought to the correct or desired value, the adjustment knob on the relay 14a is moved until the alarm 16 is sounded. The relay 14a is now adjusted to operate for the condition corresponding to the reading on the gage 44. Thereafter, the selector valve 42 is moved to provide the fiow condition designated by the arrow A. The selector valve 40 can now be moved to create the flow condition corresponding to arrow B and relay a is adjusted in the same manner as described with respect to relay 14a.

FIGURE 3 is similar to FIGURE 2 representing essentially the lower half of the basic circuit thereof. This system is used where it is desired to measure and/or provide warning for a single measured variable. Since a single variable is used, the shuttle valve 48 can be eliminated and the relay 20a'connects directly with the booster relay 50. VThe relay`20a is adjusted in exactly the same manner as described above, using the selector Valve 40 and theadjustable regulator 62.

FIGURE 4 is similar to FIGURE 2 in that an alarm system is provided for an upper limit and a lower limit; however, the upper and lower limits are applied to a single variable whose condition is sensed by a single transmitter 24. The relay'14a, for example, can be used to sense the lower limit and the relay 20a can be used to sense the upper limit. The signal from the transmitter 24 passes through the conduit 41, through the selector valve 40 (when the latter provides a flow path indicated by the arrow A), conduit 64 and on-off valves 66 and 68 to the relays 14a and20, respectively. Gages 44 and 46 are connected to the conduits 72 and 70 which lead from the valves 66 and 68 to the relays 14a and 20a respectively. The shuttle valve 48 operates in exactly the same manner described above in connection with FIGURE 2. If a signal from the transmitter reflects, for example, a decrease in liquid level below the predetermined lower limit, the pressure in the conduit 41 will be above the actuating pressure for the relay 14a such that the latter will be opened or energized to sound the alarm 16. Conversely, if the pressure in the conduit 41 should reflect a condition where the liquid level, for example, should rise above the upper limit, then the pressure transmitted from the conduit 41 to the relay 20a would be below the actuating pressure of the relay 20a such that the latter would be opened or energized, thereby sounding the alarm 16. If it is desired to calibrate the relays 14a and 20a, the regulator 62 is used in conjunction with the selector valve 40 in a manner similar to that described above in conjunction with FIGURE 2. However, the single valve 40 is used in conjunction with both relays, with the Valve 66 being open in one instance and the valve 68 being closed, or vice versa. For example, if it is desired to calibrate the relay 14a, the valve 66 is left open where the valve 68 is closed. The selector valve 40 is turned such that the flow condition lrepresented by the arrow B is provided. Regulation thereafter of the regulator 62 will provide the proper reading on the gage 44. When the proper reading on the gage 44 is reached, the relay 14a is adjusted until the alarm 16 is sounded. The relay 14a is then adjusted to the condition for level indicated by the gage 44. With the valve 66 shut and the valve 68 open, similar adjustments can be made for the relay 20a.

As indicated heretofore, the condition being sensed by the transmitter 10 or 24 need not necessarily be a liquid level. Indeed, it can be a variable pressure, hydraulic or pneumatic or it can be variable mechanical movement either rotary or translational. It can be a change in weight or volume. Practically no limitations should be placed upon the type of variable to which the present invention can be adapted. Just so long as the transmitter 10 or 24 is capable of producing an output pressure variable between 3 and 15 p.s.i., the systems described herein will be completely operable. It is well known in the art that there are many different types of transmitters or converters which are adapted to change a variable pneumatic pressure, liquid pressure or mechanical movement into a corresponding variable pneumatic pressure. Thus, the selection of a particular transmitter depends upon the type of variable being measured.

Whereas, the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications, apart from those shown or suggested herein, may be made within the spirit and scope of this invention. For example, the pressure range of the pnuematic signal has been described as being between 3 and l5 p.s.i. and the input operating pressure range of the servos has been described as being between 3 and 15 p.s.i. It should be understood that the, applicant does not intend to limit this invention to any particularA range, the above being disclosed merely for the sake of preference and in the interest of completeness of disclosure. Actually, any predetermined range can be employed just so long as the same predetermined range is used in a uniform manner. Likewise, the specific operating pressures, such as 20 p.s.i., are not at all critical, but obviously depend upon the requirements and versatility of the units which these pressures operate.

What -is claimed is:

1. A dual warning system for indicating when the instantaneous value of a first given variable falls below a first predetermined value and for indicating when the instantaneous value of a second variable exceeds a second predetermined value comprising a first sensing means for sensing the instantaneous value of said first variable and for transforming the same into a corresponding output pneumatic pressure falling within a predetermined range of pneumatic pressures, a second sensing means for sensing the instantaneous value of said second variable and for transforming the same into a corresponding output pneumatic pressure falling within a predetermined range of pneumatic pressures, a first selector valve having a first inlet connecting with the output of said sensing means, a second selector valve having a first inlet connected with the output of said second sensing means, said selector valves having second inlets connected in common and to the outlet of a regulator valve, said regulator valve having an inlet connected to a source of pneumatic pressure, said first selector valve having a single outlet, said second selector valve having a single outlet, each selector valve being individually movable to place said first and second inlets thereof alternately in communication with the outlet thereof, a first pneumatic gage connected to the outlet of said first selector valve, a first pneumatic relay connected to the outlet of said first selector valve, a second pneumatic gage connected to the outlet of said second selector valve, a second pneumatic relay connected to the outlet of said second selector valve, said gages being calibrated in units of value corresponding to the values of said first and second variables, respectively, said first pneumatic relay having an outlet and being normally closed but adapted to be opened when the pressure directedithereto `from said first sensing means indicates that the instantaneous value of said first Variable has fallen below said first predetermined value so ras to `permit passage vof". lpneumatic pressure through said first relay to the outlet thereof, said second pneumatic relay having an outlet and being normally closed but adapted to be opened when the pressure thereto from said second sensing means indicates that the instantaneous value of said second variable has exceeded said second predetermined value, a two-way check valve having two inlets and a single outlet connected such that its inlets are connected to the outlets of said pneumatic relays, respectively, an alarm device connected to the outlet of said two-way check valve, said first relay having means adjusting the same to change the pressure required to open said relay, and said second relay having means adjusting the same to change the pressure required to open said relay.

2. A dual warning system for indicating when the instantaneous value of a first given variablefalls below a first predetermined value and for indicating when the instantaneous ,value of a second variable exceeds a second predetermined value comprising a first sensing means for sensing the instantaneous value of said first variable and fortransforming the sameinto acorresponding output pneumatic pressure fallingwithin a predetermined range of pneumatic pressures, a second sensingmeans for sensing the value of said second variable and for transforming the same into a corresponding output pneumatic pressure falling within a predetermined range of pneumatic pressures, a first recording means connected to the output of said first sensing means for recording the instantaneous value of said first variable, a second recording device connected to the output of said second sensing means for recording the instantaneous value of said second variable, a first selector valve having a first inlet connecting with the output of said sensing means, a second selector valve having a first inlet connected with the output of said second sensing means, said selector valves having second inlets connected in common and to the outlet of a regulator valve, said regulator valve having an inlet connected to a source of pneumatic pressure, said first selector valve having a single outlet, said second selector valve having a single outlet, each selector valve being individually movable to place said first and second inlets rthereof alternately in communica- 8 tion with the outlet thereof, a first pneumatic gage connected to the outlet of said first selector valve, a first pneumatic relay connected to the outlet of said first selector valve, a second pneumatic gage connected to the outl let of said second selector valve, a second pneumatic relay connected to `the outlet of said second selector valve, said gages being calibrated in units of value corresponding to the values of said first and second variables, respectively, said first pneumatic relay having an outlet and being normally closed but adapted to be opened when the pressure directed thereto from said first sensing means indicates that the instantaneous value of said first variable has fallen below said first predetermined value so as to permit passage of pneumatic pressure through-said Ifirst relay to the outlet thereof, said second pneumatic relay having an outlet and being normally closed but adapted `to be opened when the pressure thereto from said second sensing means indicates that the instantaneous value of said second variable has exceeded said second predetermined value, a two-way check valve having two inlets and a single outlet connected such that its inlets are connected to the outlets of said pneumatic relays, respectively, an alarm device connected to the outlet said two-way check valve, said first relay having means adjusting the same to change the pressure required to open said relay, and said second relay having means adjusting the same to change the pressure required to open said relay.

References Cited by the Examiner VUNITED STATES PATENTS 2,248,322 7/1941 Annin 137-414 2,283,296 5/1942 Temple 137-82 2,333,300 11/1943 Dickey et al. 116-65 2,418,614 4/1947 Annin 73-302 2,596,366 5/1952 Brockett 137-82 2,832,566 4/1958 Bielstein 175-48 2,966,059 11/1960 Dower 175-48 3,075,543 1/1963 Holland 137-413 3,084,550 4/1963 Bowditch 73-391 3,086,397 4/1963 Hudson 73-302 3,100,399 8/1963 Robins 73-391 3,109,409 11/1963 Demay 116-65 3,138,956 6/1964 Falgout et al. 73-316 LOUIS J. CAPOZI, Primary Examiner.

Claims (1)

1. A DUAL WARNING SYSTEM FOR INDICATING WHEN THE INSTANTANEOUS VALUE OF A FIRST GIVEN VARIABLE FALLS BELOW A FIRST PREDETERMINED VALUE AND FOR INDICATING WHEN THE INSTANTANEOUS VALUE OF A SECOND VARIABLE EXCEEDS A SECOND PREDETERMNED VALUE COMPRISING A FIRST SENSING MEANS FOR SENSING THE INSTANTANEOUS VALUE OF SAID FIRST VARIABLE AND FOR TRANSFORMING THE SAME INTO A CORRESPONDING OUTPUT PNEUMATIC PRESSURE FALLING WITHIN A PREDETERMINED RANGE OF PNEUMATIC PRESSURES, A SECOND SENSING MEANS FOR SENSING THE INSTANTANEOUS VALUE OF SAID SECOND VARIABLE AND FOR TRANSMITTING THE SAME INTO A CORRESPONDING OUTPUT PNEUMATIC PRESSURES FALLING WITHIN A PREDETERMINED RANGE OF PENUMATIC PRESSURE, A FIRST SELECTOR VALVE HAVING A FIRST INLET CONNECTING WITH THE OUTPUT OF SAID SENSING MEANS, A SECOND SELECTOR VALVE HAVING A FIRST INLET CONNECTED WITH THE OUTPUT OF SAID SECOND SENSING MEANS, SAID SELECTOR VALVES HAVING SECOND INLETS CONNECTED IN COMMON AND TO THE OUTLET OF A REGULATOR VALVE, SAID REGULATOR VALVE HAVING AN INLET CONNECTED TO A SOURCE OF PNEUMATIC PRESSURE, SAID FIRST SELECTOR VALVE HAVING A SINGLE OUTLET, SAID SECOND SELECTOR VALVE HAVING A SINGLE OUTLET, EACH SELECTOR VALVE BEING INDIVIDUALLY MOVABLE TO PLACE SAID FIRST AND SECOND INLETS THEREOF ALTERNATELY IN COMMUNICATION WITH THE OUTLET THEREOF, A FIRST PENUMATIC GAGE CONNECTED TO THE OUTLET OF SAID FIRST SELECTOR VALVE, A FIRST PNEUMATIC RELAY CONNECTED TO THE OUTLET OF SAID FIRST SELECTOR VALVE, A SECOND PNEUMATIC GAGE CON-

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