US2919910A - Air pressure control system - Google Patents

Description

Jan. 5, 1960 c. M. OLEARY 2,919,910

AIR PRESSURE CONTROL SYSTEM Filed June 3, 1958 I 2 Sheets-Sheet 1 Cape/.55 4/. 0254?) 1 N VEN TOR.

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irraeA/fy United States Patent AIR PRESSURE CONTROL SYSTEM Charles M. OLeary, Los Angeles, Calif.

Application June 3, 1958, Serial No. 739,499

14 Claims. (Cl. 267-1) This invention relates to air balanced oil well pumping units and more particularly to maintaining the balancing pressure of the air balancing system in step with the varying loads imposed on the air balancing unit due to changes in well load conditions, which will require an addition or reduction of air pressure to the balancing system, to maintain the well load in relatively perfect balance under varying well load conditions.

It is well known to those in the art of oil well pumping, that slugs of water enter the well bore and must be pumped to the surface, and that water is heavier than oil, which increases the counter-balance load. When the water slug is removed, gas moves in and lightens the counter-balance load, or the fluid flow to the well bore may be in spasmodic amounts of the mixture of oil and gas which aflects the well load. 1 All of the preceding conditions are variable and change from time to time during the pumping operations As an example, the gas pressure increases and decreases with the tides in the coastal areas. Also, the water flow into the well bore increases with the oceans mean high and mean low tide. Many other factors, too numerous to mention, influence the well counter-balancing loadings.

It will be noted that when the well load builds up above the normal balancing pressure that the time cycle between the up and down-stroke of the well pumper changes, making a longer time period on the up-stroke of the air-balancing unit; and when the'well load is light, the time cycle is faster on the up-stroke than on the down-stroke.

When the Well load is nearly perfectly balanced, the time cycle between the up and down-strokes are approximately equal.

It is also well known in the art of air counter balancing of oil well pumping units, that the air pressure in the system is higher at the bottom of the pumping stroke than at the top of the stroke. "This pressure variance can be as much as 60 p.s.i. between the up and downstrokes of the air balancing systems air pressure.

An object of this invention is to provide a fluid responsive device which is affected by the pressure buildup and pressure drop time cycle between the up and down strokes of the air-balanced pumping units counterbalancing systems pressure changes.

A further object of this invention is to provide a time cycle fluid responsive device that will release air pressure from the balancing system when the down stroke exceeds a predetermined time cycle and to build up pressure in the system when the up stroke time cycle drops below a predetermined time cycle.

It is an object of this invention to maintain the time cycle between the up and down strokes of the pumping unit as nearly equal as possible.

It is an object of this invention to relieve the prime mover of the pumping unit, .the belt drive and gear box, as Well as all of the associated parts from overload conditions by controlling the counterbalance forces in step with the varying well-load changes at all times.

2,919,910 Patented Jan. 5 1960 An object of this invention is to, provide acompletely automatic, infinitely variable pressure control system for air balanced oil well pumping units, wherein the balancing pressures range from 100 p.s.i. to as much as 500 p.s.i.

Figure l is a fragmentary side elevation view of an air balance oil well pumping unit partially in section and partially in elevation with parts of the pumping unit eliminated from the drawings for brevity, but are wellknown to those in the art. The pitman head bearing 4 is attached to the walking beam 1, and is pivotly connected to pitman arm 8, which is pivotly connected to a crank arm, not shown, and a speed reducer also not shown, to produce a reciprocating motion to walking beam '1, when the crank, not shown, is rotated as is well known in the art. The balance cylinder beam bearing 12, is bolted to walking beam 1. Cylinder head 20 is connected to the walking beam 1 by connector pin 16,

which forms a pivotal connection between the walking beam 1, the air balancing cylinder 32, and air receiver clamping flange 22. This permits the air balance cylinder 32, air receiver 24 and clamping flange 22, which is fixedly attached to air balance cylinder 32, to move vertically with the oscillatory motion of the walking beam 1.

Air balance piston assembly 40, as shown, is in air balance cylinder 32, and is fixedly attached to hollow piston rod 4'4, which rests upon fixed base 60, and is pivotly associated therewith through piston rod ball pivot 56. The piston 40, and piston rod 44, which is pivotally mounted on the fixed base 60, forms a closure for the lower end of the air balance cylinder 32, except for fluid passages which will hereinafter be described. As stated, air balance piston assembly 40 forms the lower closure for the air balance cylinder 32. Cylinder head 2i? forms the upper closure for air balance cylinder 32.

Air ports 28 are provided at the upper end of air balance cylinder 32, to pass air freely to and from air balance cylinder 32 to air receiver 24.

The upper end of the air balance piston assembly 40 is provided with hollow piston rod air ports 36, which withdrawing air pressure from the balancing systems air receiver 24 and balance cylinder 32, through passage described.

Air passage 68 is threaded and receives air line 72. Air line 72 is threaded at its opposite end and is screwed into pipe cross 76. The upper end of pipe cross 76 receives vertical pipe line 80 which is threaded thereto. The upper end of pipe line 80 is threaded and connects to pipe elbow 89, into which pipe line 88 is threaded. The opposite end of pipe line 88 is threaded to receive check valve 92 which opens toward the hollow piston rod 44. Pipe line 96 is threaded to check valve 92 at one end and connected by threaded means to air compressorltlll. Air compressor 100 is driven by electric motor 1% by suitable belts and pulleys as indicated at 103. 112 indicates a power source for electric motor Til-t and 12d indicates a starting switch for electric motor 104.

Power line 116 is from the power source 112 to starting switch 12a) back to electric motor 134. Power line 12a is from starting switch 124 to switch 128. In the system, a manual switch, not shown, is provided to initially build up air pressure in the system, before oil pumping operations are started.

The switch 123 is provided with an actuator stem 132, and is spaced from switch actuator stem 136 which projects from double-acting diaphragm housing 140. The diaphragm extension stem 144 which projects from the opposite end of double-acting diaphragm housing 140 carries a reduced diameter 138 which is spaced from the pressure release mechanism of the unloader valve 148. The double-acting diaphragm housing 140 consists of two halves, 3G0 and 304, which are separated by diaphragm member 212.

From the pipe cross 76 a pipe line 156 is provided, which, at one end, is threaded into pipe cross '76, and at the other end into pressure volume control valve 160. It will be noted that the pressure volume control valve 160 may be used as a fully opened and fully closed valve or may be used as a fluid flow modulator valve, depending upon the dampening effect of the fluid flow desired to be maintained, in the air pressure control system.

Extending from the pressure volume control valve 16% is pipe line T64 which is threaded at one end to valve res and at the other end to elbow 168, into which is also threaded pipe line 172 which at one end is threaded into elbow 176. A nipple 192 connects elbow 176 to pipe T 18% which, when valve 160 is in the open position, provides an open fluid flow passage from the air balancing systems pressure fluctuations. Extending from pipe T 186 are two pressure lines, 188 and 184, which connect directly into the double acting diaphragm housing 1%, into housing sections 300 at 200, and housing section 3% at 1% through fluid ports 276 and 280 as shown in the drawings. it will be noted that pressure line 188 is a coiled section and that pressure line 134 is also coiled and, further, that the number of coils in line 188 are fewer than the number of coils in line 184. Now referring directly to the coils T88 and 184, the said coils are of drawn tubing of very small diameter, approximately one to two-thousandths of an inch internal diameter, or larger in diameter if necessary. The length and internal diameters provide a dampening effect, the fluid flow resister eflect depending upon the internal diameter and the lengths of the fluid resister tubes 1% and 184 which connect into the double acting diaphragm housing 140 and diaphragm housings 300 and 304 as stated above.

In Figure 2 or" the drawings, a cross section of the double acting diaphragm housing 140 is shown. The double acting diaphragm housing 140 consists of two dished housings, 34M) and 304, which are separated from each other by the flexible diaphragm member 212. A series of bolts, 272, clamp the dished housings 3% and 3&4, to the flexible diaphragm member 2122, resulting in forming two separate pressure chambers, as indicated at 28-1 and 288 in the drawings. The pressure chamber 234 is provided with a fluid passage 276, which permits fluid pressure to either flow into or discharge from the chamber 284, through connector 260 and resistor line 188. Also the pressure chamber 288 is provided with a fluid passage 28% which permits fluid pressure to either flow into or discharge from the chamber 288 through the connector 196 and resistor line 184.

The flexible diaphragm 212 has a central passage as indicated at 221. The diaphragms actuator stern fits snugly into the passage 221. The diaphragm actuator stem 258 is threaded as indicated at 227. The diaphragm plates, 216 and 217, slip over the threaded portions of actuator stem 228 and are clamped to the flexible diaphragm member 212 by the diaphragm piston rod clamping bolts 22@.

The diaphragm actuator stem 228 is provided with two extensions, 13-6 and 144, which are smaller in diameter than the threaded portion of the diaphragm actuator stem 22%. The said small diameter extension 136 passes through the dished housing sea as indicated at 136, in the drawings, and is sealed by 0 ring is dished housing 3 3i). Also the smaller diameter extension 144 passes through the dished housing 3%, as indicated at 144 in the drawings, and is sealed by O ring 292 in dished housing 304-. Opposite the extension 136 of the diaphragm actuator stem 228, which projects beyond the dished housing 3'90, is provided an electric switch 128, and its actuator stem 132, which is spaced from the said stem 136. It will be noted that the electric switch 123 is in the normally ofl position; also that the flexible diaphragm member of the double acting diaphragm is in its neutral position. The diaphragm extension 144 of the diaphragm actuator stem 2% which projects beyond the dished housing 3M and carries a second reduced diameter as indicated at 138. The outermost end of said extension 1133 in the neutral position of the flexible diaphragm 212 is spaced from the pressure relief valve 24-4 in pressure relief valve housing 143.

Pipe line 1:32 is threaded at both ends, one end of which is threaded into pipe T 76 and the other into the pressure relief valve 148 which, when in an open posi tion, releases air from the balancing system, as will be more fully described.

The pressure reliet valve housing 148 contains chamber 2 55 and a fluid discharge port 256 which, at one end, communicates with chamber 261 which is ported at 260 to the atmosphere. The chamber 261 is also ported at 26 3- to receive check valve actuator stem 138.

The said fluid discharge port 256 forms a ball check valve seat in chamber 245 as indicated at 252. A ball check valve 244 is shown in a seated position and is held seated by ball check valve spring 248 which abuts to the bushing The pressure relief valve housing 148 carries a threaded bushing 24% which is ported at 251, as indicated in the drawings, which screws into the pressure relief valve housing into the threaded bushing 2% is threaded pressure line 152, the opposite end of which is threaded into pipe '5'- 76, and forms an unobstructed communication from the air receiver 24, balance cylinder 32 and hollow piston rod 44.

The operation of the device and all related structure is as follows: Assume that the air pressure is supplied to the closed system fluid receiving unit by the air or fluid supply source, which is the air compressor 1%, electric motor W4 and all related structure. The air pressure build-up comes under the isothermal compression formula between the balance cylinder 32, the air receiver 24, the piping between check valve 92, in the air pressure supply line to the balancing cylinder 32, and the air line supplying air pressure to the double acting diaphragm housing 3 through the pressure volume control valve 16h up to the pipe T 1%.

The pressure volume control valve res monitors, meters, or controls the flow of air to the restrictor lines 384 and This monitoring is maintained when air flows to or from the restrictor lines 184 and 183. In other words, the pressure volume control valve provides a cushion for the restrictor lines 184 and 188. it is possible to leave the valve Mil out of the system, but it is preferred to have it in, for the reason that it could provide, in the absence of any other function, a cut off valve.

Furtherv the fluid restriction lines 1134 and 138 are limited to a very small internal diameter of two to three thousandths of an inch, which produces a high frictional flow resistance in either direction of air flow.

Assume the walking beam 1 was making 20 strokes per minute. This would allow only 1.52 seconds for the 5 down stroke and 1.48 seconds to reach its maximum low pressure. Therefore, if the up and down time increments are relatively equal, the pressure in the diaphragm chambers 284 and 288 is relatively constant. The time cycle between the up and down strokes is not suflicient to provide any appreciable pressure change in either of the chambers. If the time cycle on the down stroke is materially longer than on the up stroke this would be an indication of the air balancing unit being over counter balanced. In this instance, a greater volume of air will be delivered to the diaphragm chamber 284 through fluid restrictor line 188, due to its shorter length it provides a smaller magnitude of fluid pressure resistance than through restrictor line 184. In other words, if the down stroke of the walking beam and all the attached equipment is longer than the up stroke, then an air pressurehas been established in the air receiver 24 for a longer period of time. As a result of this increased time, the air pressure backs through the system until it reaches the restrictor lines 184 and 188. Due to the fact that line 188 has a smaller resistance than line 184, more air passes into chamber 284. This increase in pressure in chamber 284 deforms the diaphragm in the direction of valve 148. When the pressure in chamber 284 becomes great enough the stem extension 138 on the end 144 of stem 228 is urged against the spring loaded ball check 244. This unseats the ball check 244. Unseating the ball check releases some of the pressure in the system.

The released air pressure now passes from the air receiver 24 through the ports 36, in the piston assembly 40,

through the hollow piston rod 44, the port 68, pipe 72,

pipe cross 76, pipe 152, and out opening 260. When sufficient pressure has been released the time cycle be tween the up and down strokes assumes a more equal condition. This permits the excess air that is in chamber 284 to return to the system through the restrictor line 188 and the diaphragm resumes its normal form which results in releasing the stem extension 138 from engagement with the ball check valve 244.

It may be seen, after the above description, that a greater volume of air will be delivered to chamber 284 than to chamber 288. As a result of the diflerential of time in the time cycles, between the up and down strokes, airin chamber 284 cannot flow out as fast as it entered. This causes an air pressure build up in chamber 284.

The pressure build up in chamber 288 is slower to reach the time cycle change due to the greater length of the fluid restrictor line 184. The difference in the time period permits the increased pressure in the diaphragm chamber 284 to flex or deform the diaphragm 212. Deforming the diaphragm urges the diaphragm stem 228 toward the unloader valve 148 to release air pressure from the air balancing system to establish a relatively equal up and down stroke time cycle.

Now, assuming the wall load is under counter balanced, the walking beam on the down stroke drops faster due to the reduced resistance of the lower pressure in the balancing system which unloads the prime mover. On the up stroke, the load is heavier due to the under counter balancing of the load. 4

Now considering the time cycle of the up stroke, which is greater now than on the down, air passes into the air receiver 24 for a longer length of time than it passes from the receiver. As before stated, the air compressor is in the normally off position. Since the entire system is closed and there has initially been a pressure build up that was equal, particularly in the chambers 284 and 288, air to the receiver 24 must be obtained from the system. When the up stroke is of a greater length of time than the down stroke, air is permitted to pass from the chambers 284 and 288 for a greater length of time. Due to v the fact that fluid restrictor line 188 has a smaller magnitude of fluid pressure resistance than line 184, air is permitted to pass from chamber 284 in a greater volume than from chamber 288. The result of this is that the excess pressure in chamber 288 deforms or flexes the diaphragm 212 toward switch 128. End 136 of the stem 228 engages the plunger 132 of the switch which results in closing the electrical circuit to actuate the air compressor 100. Actuation of the compressor results in putting air into the system. Until such time as the pressure build up in the systems air counter balancing unit reaches a point where the time cycle between the up and down strokes again become relatively equal, at which time the flexible diaphragm 212 moves to its neutral position moving stem 136 away from switch actuator stem 132 deactivating electric motor 104 and air compressor 100.

The diaphragm chamber 288 and its restrictor line 184 which are in direct communication with the air balancing system forms a mean average pressure chamber. The diaphragm chamber 284 also forms a mean average pressure chamber when the time cycles between the up and down strokes of the well pumping unit are relatively equal. However, the diaphragm chamber 284 is-more responsive to well load conditions and the pressure therein will not represent the mean average pressure when the time cycle between the up and down strokes changes, which will cause the flexible diaphragm 212 to move in one direction or the other, to either release or build up air pressure in the air balancing system.

In the final summation of the operation of the fully automatic, infinitely variable, pressure control system for air balanced oil well pumping units, wherein the balancing air pressures range from p.s.i. for shallow Wells up to 500 p.s.i. for extremely deep wells, this unit requires no adjustments or modification between the air pressure ranges hereinbefore set forth. The magnitude of the fluid restrictor lines 188 and 184 are of such length and proportion as to provide an infinitely variable time cycle pressure control to the double acting diaphragm member to maintain the time cycle between the up and down strokes of an air balanced oil pumper relatively constant, regardless of the well depth and the required air balancing pressure.

-It is also to be understood that the electric switch 128 may be substituted with an air pressure control valve to actuate an air compressor not electrically driven.

While in order to comply with the statute, the invention has beendescribed in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed comprises a preferred form of putting the invention into effect, and the invention is therefore claimed in any of its forms or modifications within the legitimate and valid scopeof the appended claims.

What is claimed is:

1. In an air pressure control system having a fluid supply source and a normally pressurized closed fluctuating reciprocating fluid receiving unit, connected to said source; a fluid pressure control system between and connected to said source and unit comprising a housing; a switch and valve actuating resilient means in said housing that divides the latter into a pair of chambers; an element extending outwardly of each chamber and connected to said means; fiuid flow restrictor structure connected to said housing and in communication with each chamber; a fluid carrying conduit connected to said source, said unit and said restrictor structure; mechanism associated with one element to actuate said fluid source and mechanism associated with the opposed element to relieve pressure in said unit.

2. In an air pressure control system having a fluid supply source and a normally fluctuating pressurized closed system reciprocating fluid receiving unit, connected to said source; a fluid pressure control system between and connected to said source and unit comprising a housing; a switch and valve actuating resilient means in said housing that divides the latter into a pair of chambers; an element extending outwardly of each chamber and connected to said means; fluid flow restrictor structure connected to said housing and in communication with each chamber; a fluid carrying conduit connected to said source, said unit and said restrictor structure; mechanism associated with one element to actuate said fluid source and mechanism associated with the opposed element to relieve pressure in said unit; said resilient means being a diaphragm.

3. In an air pressure control system having a fluid supply source and a normally fluctuating pressurized closed system reciprocating fluid receiving unit, connected to said source; a fluid pressure control system between and connected to said source and unit comprising a housing; a switch and valve actuating resilient means in said housing that divides the latter into a pair of chambers; an element extending outwardly of each chamber and connected to said means; fluid flow restrictor structure connected to said housing and in communication with each chamber; a fluid carrying conduit connected to said source, said unit and said restrictor structure; mechanism associated with one element to actuate said fluid source and mechanism associated with the opposed element to relieve pressure in said unit; said structure comprising at least one fluid resistance carrying tube.

4. In an air pressure control system having a fluid supply source and a normally fluctuating pressurized closed system reciprocating fluid receiving unit, connected to said source; a fluid pressure control system between and connected to said source and unit comprising a housing; a switch and valve actuating resilient means in said housing that divides the latter into a pair of chambers; an element extending outwardly of each chamber and connected to said means; fluid flow restrictor structure connected to said housing and in communication with each chamber; a fluid carrying conduit connected to said source, said unit and said restrictor structure; mechanism associated with one element to actuate said fluid source and mechanism associated with the opposed element to relieve pressure in said unit; said structure comprising a pair of coiled fluid carrying tubes.

5. In an air pressure control system having a fluid supply source and a normally fluctuating pressurized closed system reciprocating fluid receiving unit and connected to said source; a fluid pressure control system between and connected to said source and unit comprising a housing; a switch and valve actuating resilient means in said housing that divides the latter into a pair of chambers; an element extending outwardly of each chamber and connected to said means; fluid flow restrictor structure connected to said housing and in communication with each chamber; a fluid carrying conduit connected to said source, said unit and said restrictor structure; mechanism associated with one element to actuate said fluid source and mechanism associated with the opposed element to relieve pressure in said unit; said structure comprising a pair of restrictor fluid carrying tubes, interconnected to said pair of chambers, one of which has a greater magnitude of fluid pressure restriction than the other.

6. An air pressure control system having a fluid supply source and a normally pressurized closed system reciprocating fluid receiving unit, connected to said source; a fluid pressure control system between and connected to said source and unit comprising a housing; a switch and valve actuating resilient means in said housing that divides the latter into a pair of chambers; an element extending outwardly of each chamber and connected to said means; fluid flow restrictor structure connected to said housing and in communication with each chamber; a fluid carrying conduit connected to said source, said unit and said restrictor structure; mechanism associated with one element to actuate said fluid source and mechanism associated with the opposed element to relieve pressure in said unit; said mechanism comprising a switch to actuate said fluid source.

7. In a differential air pressure control system having a fluid supply source and a normally pressurized closed system reciprocating fluid receiving unit, connected to said source; a fluid pressure control system between and connected to said source and unit comprising a housing; a switch and valve actuating resilient means in said housing that divides the latter into a pair of chambers; an element extending outwardly of each chamber and connected to said means; fluid flow restrictor structure connected to said housing and in communication with each chamber; a fluid carrying conduit connected to said source, said unit and said restrictor structure; mechanism associated with one element to actuate said fluid source and mechanism associated with the opposed element to relieve pressure in said unit; said second mentioned mechanism comprising a ball check valve.

8. A time cycle control mechanism for air balanced oil well pumping units comprising two separate pressure chambers of relatively equal volume, the said two separate pressure chambers being separated by a flexible diaphragm member; a piston member fixedly attached to said flexible diaphragm and extending through and beyond said pressure chambers; a pressure release mechanism spaced from one end of said piston member on one side of said piston extension; a pressure build up mechanism spaced from the other end of said piston; 21 pair of fluid flow resistor lines communicating with the interior of each of said pressure chambers at one end and communicating at the other end with the pressure within the said air balancing system, said fluid flow resistor lines having difierent fluid flow characteristics from each other, operable upon a change between the time cycle between the up and down strokes of said air balanced oil pumping unit to cause movement of said piston member to either release pressure from said air balance system or to build up pressure in air balance system.

9. In an air pressure control system having a fluid supply source and a normally pressurized closed fluctuating reciprocating fluid receiving unit, connected to said source; a fluid pressure control system between and connected to said source and unit comprising a housing; a switch and valve actuating resilient means in said housing that divides the latter into a pair of chambers; an element extending outwardly of each chamber and connected to said means; fluid flow restrictor structure connected to said housing and in communication with each chamber; a fluid carrying conduit connected to said source, said unit and said restrictor structure; mechanism associated with one element to actuate said fluid source and mechanism associated with the opposed element to relieve pressure in said unit; said elements being switch and valve actuating extensions.

10. In an air pressure control system having a fluid supply source and a normally pressurized closed fluctuating reciprocating fluid receiving unit, connected to said source; a fluid pressure control system between and connected to said source and unit comprising a housing; a switch and valve actuating resilient means in said housing that divides the latter into a pair of chambers; an element extending outwardly of each chamber and connected to said means; fluid flow restrictor structure connected to said housing and in communication with each chamber; a fluid carrying conduit connected to said source, said unit and said restrictor structure; mechanism associated with one element to actuate said fluid source and mechanism associated with the opposed element to relieve pressure in said unit; said resilient means and structure comprising a diaphragm and a pair of coiled fluid carrying tubes respectively.

11. In an air pressure control system having a fluid supply source and a normally pressurized closed fluctuating reciprocating fluid receiving unit, connected to said source; a fluid pressure control system between and connected to said source and unit comprising a housing; a switch and valve actuating resilient means in said housing that divides the latter into a pair of chambers; an element extending outwardly of each chamber and connected to said means; fluid flow restrictor structure connected to said housing and in communication with each chamher; a fluid carrying conduit connected to said source, said unit and said restrictor structure; mechanism associated with one element to actuate said fluid source and mechanism associated with the opposed element to re lieve pressure in said unit; said resilient means and elements comprising a diaphragm and a switch and valve actuating extensions respectively.

12. In an air pressure control system having a fluid supply source and a normally pressurized closed fluctuating reciprocating-fluid receiving unit, connected to said source; a fluid pressure control system between and connected to said source and unit comprising a housing; a switch and valve actuating resilient means in said housing that divides the latter into a pair of chambers; an element extending outwardly of each chamber and connected to said means; fluid flow restrictor structure connected to said housing and in communication with each chamber; a fluid carrying conduit connected to said source, said unit and said restrictor structure; mechanism associated with one element to actuate said fluid source and mechanism associated with the opposed element to relieve pressure in said unit; said resilient means and structure comprising a diaphragm and a pair of coiled fluid carrying tubes respectively.

13. In an air pressure control system having a fluid supply source and a normally pressurized closed fluctuating reciprocating fluid receiving unit, connected to said source; a fluid pressure control system between and connected to said source and unit comprising a housing; a switch and valve actuating resilient means in said housing that divides the latter into a pair of chambers; an element extending outwardly of each chamber and connected to said means; fluid flow restrictor structure connected to said housing and in communication with each chamber; a fluid carrying conduit connected to said source, said unit and said restrictor structure; mechanism associated with one element to actuate said fluid source and mechanism associated with the opposed element to relieve pressure in said unit; said resilient means and structure comprising a diaphragm and a pair of restrictor fluid carrying tubes, interconnected to said pair of chambers, one of which has a greater magnitude of fluid pressure restriction than the other respectively.

14. In an air pressure control system having a fluid supply source and a normally pressurized closed fluctuating reciprocating fluid receiving unit, connected to said source; a fluid pressure control system between and connected to said source and unit comprising a housing; a switch and valve actuating resilient means in said housing that divides the latter into a pair of chambers; an element extending outwardly of each chamber and connected to said means; fluid flow restrictor structure con-- nected to said housing and in communication with each chamber; a fluid carrying conduit connected to said source, said unit and said restrictor structure; mechanism associated with one element to actuate said fluid source and mechanism associated with the opposed element to relieve pressure in said unit; said resilient means and mechanism comprising a diaphragm and a switch to actuate said fluid source respectively.

References Cited in the file of this patent UNITED STATES PATENTS

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