US2961147A - Control system for fluid compressors - Google Patents

Description

Nov. 22, 1960 H. c. osTERKAMP CONTROL SYSTEM FOR FLUID COMPRESSORS Filed April 7, 1958 INVENTOR. HENRY C. USTERKAMP V- aayds -1 Allam@ .mail

United States atent O CONTROL SYSTEM FOR FLUID COlVIPRESSORS Henry C. Osterkamp, Elm Grove, Wis., assigner to Westmghouse Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvania Filed Apr. 7, 1958, Ser. No. 726,923

3 Claims. (Cl. 230-9) This invention relates to control mechanisms for nid compressors of the motor driven type. More particularly the invention relates to dual control mechanisms for simultaneously controlling both the compressor Speed and air intake, at least over part of the compressor load range, in accordance with the discharge pressure of the compressor.

Control devices of this nature are in use which control the output of the compressor by varying its speed over a portion of its load range. Over another portion of the compressor load range, the compressor output is controlled by simultaneously varying the compressor speed and controlling its rate of air intake. These prior art devices utilize complicated control mechanisms which are inflexible as to where and how they can be installed on the compressor-motor unit; present service and maintenance problems, and furthermore make it diicult to diagnose and locate the part needing repair or replacement. It can be appreciated that any malfunctioning of the unit should be quickly located and corrected without unnecessary disassembly of associated parts.

Accordingly, the present invention provides a comparatively simple and compact control mechanism for a duid compressor unit, which mechanism is easy to install, the various parts of which are easy to service and any part of which that needs adjustment or repair can be quickly isolated and corrected without affecting the adjustment of associated parts. More specifically, the control valve, speed control valve and intake control valve are independently mounted which facilitates diagnosing of trouble and permits exibility of application.

The present invention provides a control system for controlling the output of a iluid compressor in accordance with its discharge pressure by simultaneously regulating both the compressor motor speed and the intake of the compressor. This aspect of the invention further contemplates that the limits of the discharge pressure range over which the compressor motor speed is adjustable, can be varied within the range of discharge pressure over which the compressor intake valve is variable. Thus the speed control is effective intermediate the intake control range and can be varied for the most suitable engine speeds.

A control system of the above type is provided by this invention which provides automatic drainage of condensate from the controls, is economical to produce, reliable in operation and ecient in performing its intended functions.

These and other objects and advantages of the present invention will appear hereinafter as this disclosure progresses, reference being had to the accompanying drawings in which:

Figure l is a schematic diagram of a compressor-motor unit embodying a control system made in accordance with the present invention, certain of the parts being shown in section, broken away or removed for clarity in the drawings, and

Figure 2 is a controls response curve which is charac- 2,951,147 Patented Nov. 22, 1960 ice teristic of the present system and in which curve the compressor capacity is plotted against the discharge pressure.

Referring in greater detail to the drawings, the cornpressor 10 is shown as being of the rotary type but may be any other type which serves to compress air or other uids, and is driven by a power source shown here as an internal combustion engine 12. The engine has a conventional governor 14 which controls the speed of the engine through suitable and conventional linkages, not shown.

The compressor discharges fluid under pressure through conduit 15 and into the receiver 17 from which it may be drawn as needed via service valve 18 to actuate pneumatic tools or other machinery (not shown).

The system includes a control valve 20 having a chamber 21 that receives discharge pressure from the receiver via conduit 22. The control Valve 26 is preferably located in the highest point of the system so that any condensate forming therein will drain to other parts by gravity. Valve 20 is actuated in response to variations in compressor discharge pressure to control both the air inlet and the speed of the compressor, as follows.

Cooperating with the control valve 2i) and connected therewith at a common point 23 is an inlet valve actuating mechanism 25 for controlling the rate of air tiow into the compressor, and an engine speed control mechanism 26. Mechanism 26 is connected directly to the governor 14 and has a link connection therewith to control the speed of the engine.

Mechanism 25 is actuated in response to variations in compressor discharge pressure for shifting the inlet valve 28 positioned in the compressor intake chamber 29.

The control valve 20 and the air inlet control 25 both act throughout the entire load change range of the compressor. This valve starts to open at a predetermined minimum pressure, for example p.s.i., and permits air to flow from conduit 22 to conduit 38 up to a maximum of say 1l() p.s.i., or the dierential attainable by controls 25 and 26. After achieving maximum opening, the valve 20 gradually closes again until the pressure is 100 p.s.i. The speed control 26, however, is adjustable as to that portion of the compressor load change range in which it will function. In other words, the air inlet control 25 is effective over the entire load change range to change the output of the compressor, while the speed control 26 can be made to elect speed changes of the engine, and thus vary the compressor output, over any selected portion of the compressor load change range.

In this manner the advantages of dual control speed and intake can be utilized in the lower portion of the load change range. At the upper portion of the load change range when higher discharge pressure develops, the air inlet may be varied, and the engine speed may be maintained at a predetermined minimum to prevent its stalling.

If desired for other operating conditions, the speed and intake may both be varied simultaneously over the entire load range of the compressor.

The control valve 20 comprises an upper body 35 secured to a lower body 31 and between which is secured a diaphragm 32. A valve needle 33 is carried by the diaphragm and is engageable with a valve seat 34 carried by the lower body 31. The needle 33 is held in the seated position by spring 35, the force of the latter being variable by the manually operated handle 36. The force of the spring is adjusted by handle 36 so the valve remains closed until the pressure in chamber 21 reaches a predetermined amount. For example, assume that it is desired to maintain a discharge pressure of 100 p.s.i. in the upstream'or high side'of'the'system. The control valve 20 would be set so that when pressure above'this'predetermined maximum of 100 p.s.i. was reached in the chamber 21the diaphragm would raise against the force of spring K 35 to lift the needle off its seat; therebyadmittingepressure' flidtoconduit 38;

Thus the operation of the control valve 20 is such that aj Variable pressure of from O to100 psri.I will exist in chamber 21V duringoperation ofthe system; thevailveeSSredetail.

It will be noted that thepressure duid from the control valve 20 is distributedfrom the-common-point23^`toethe air'inlet controlrnechanism via passage 40'andto speed" control mechanism 26 via line 41,' and both controlsY 25 and 26 may be operated simultaneously when'excess pressure is discharged from the regulator' or control'valve'20.

Air inlet valve actuator 25 comprises ya rolling bellows type diaphragm 44 which is secured betweenthe tubular casing portion 45 of the housing 29and'the endrhousing 46, thus forming two chambers 47 'and'.48. The particular type of diaphragm shown is more reliable for applications of this nature because it is more resistant to the wearing action imposed by the continual flexing than is a tight'type diaphragm. A piston Stl'is secured to the bellofram 44 by means of the plate 51 which engages the opposite side ofthe bellofram and is held captive on the pistonrod' 52'by the nut 53 threaded on the end of the rod. The rod is slidably mounted in the housing 29 and a valve disc 54 is slidably mounted on the other, end of the rod. Disc 54 is engageable with the gasket seat 55 'when in the Sealing position. The light spring 56 constantly urges the valve 54 to the closed position and serves to close the valve when the compressor is shut down. Thus the valve,

is free to close, independently of its regulating mechanism, when the compressor stops, and is urged to the closed position by spring 56 or reverse uid' flow at the compressor intake. The spring 56 is only of such strength so the impact of fluid flowing Yat a relatively low rate through opening 58 is sufficient to hold the valveY 54 in the open position.

Thus when pressure duid is admitted to chamber 48'to overcome the force of spring 60, the piston 50 and itsA associated valve 28 are urged to the left (Fig. l) toward the sealing position to throttle or cut off the ow of airv through the compressor. A breather 61 is provided in chamber 47 for permitting condensate to escape theretrom. This breather also prevents reverse roll-up ofthe bellofram when the compressor is stopped and the valve inlet chamber pressurized and in communication with,

chamber 47 due to the free fit of rod 52.

The engine speed control unit 26 comprises a tubular body 65 which is secured at one end to the governor 14.`

A cup-shaped end cap 66 is secured to the other end of the body and a rolling bellows diaphragm 67 is secured between body 65 and cap 66 to define a chamber 68. Conduit 41 communicates with chamber 66 and unit 26 is, thereby responsive to pressure variations at theoutlet of control valve 2t). Y

An orice 70 is located at the lower, side of the charn-Y Vdensate from the system. This orice controls the pressure on the downstream or lowery side of the system and for this purpose could be located elsewhere in thevdownstream side, that is, on the outlet side` of the valve 20.

The orifice continuously bleeds ofi? air after the controlV valve 20 opens and eiects a response inthe system. The

sizeof the orice 70`is determined by the eiective areaupon which the pressure may act to move mechanism 25A and also on the responsiveness and size of valve 33 and vits ability-to regulate-the-flow of air therethrough.A These dimensions may all be variable, of course, but it is desirable to have the downstream pressure as close as possible to the upstream pressure, and still get good response (not close the controls) in order to have the maximum amount of force available to actuategthe mechanisms 25 and 26.

Mechanism 26 also includes a pistonV 72 connected to the belloram l-67 -by the-plate73'f-and'bolt\74. A spring 75 acts against the pistonr and'tendsto urge it to thefast Byvreferring to Figure Zit willfbe seenY thattherange of engine speed may be adjustable anywhere within the range of operation of the intake valve. In the setting'shown by Figure 2when the compressor is operating andgthe discharge pressure rises above lO0.p.s.i. the intake valve starts to close before the` engine speed decreases. By adjusting the screw` 80, the point atwhich the engine speed changes may be varied; for example, the point at whichv the engine speed starts` to drop under these conditions may be made to coincide with thefpoint at which ,the air intakevalve starts to close. The .same regulation maybe made at the lower end of the compressor. load range, but it. has been found desirable` tolocate the lowerv limit of the speed range at a pointconsiderably before the intake valve closes completely.

The presenty invention providesv acontrol system in which the speed modulation is intermediate or simultaneous to the airy intake modulation. There is noi need to maintain yarconstantforce on the inlet valve in a direction oppositeto that imposedv by` the outlet pressure of the control lvalve, and thusthe necessity of considerable equipment, such as reducingvalves, plumbing and the like, is notrequired;

In the present arrangement, the speed control 26 can be-.located adjacent the governor and only a conduit41is requiredY between the control valve` 20 and control.26, no complicated linkage or adjustments being :necessary toiactuate the governor; In-otherv words, the uid operatedfmechanism 26is separately. mounted adjacentV the governor and independently` of the control valve 20. As a; result, flexible mountingof the system'is-possible and, furthermore, it any elementofV any of the controlmech-l anismsfaihsuch as adiaphragm, the faulty element can be easily: located andl ,repaired or replacedV without' disassemblingA-the othen mechanismsjor affecting theiradjustment.

Various modes of'carrying'out the invention are contemplated asbeing within the-scope ofthe following claims particularly pointing out and distinctly claimingV-thesubject matter-whichis regarded as theinventiom Lin combination, a iluid compressor, a motor drivingly connected to said compressor, a controlV valve in fluid communication with said compressor'and responsive to-variations incompressor discharge-pressure, said controlvalve having anoutlet conduit through which pressure iluid over a predetermined Value isdischarged, agovernor mounted on said motor for regulating the speed-thereof, afluid pressure operated speed'control mechanism and having an operating link connectedwith the'governorv-or shiftingrsaid governor between slow and; fast positions, a conduit placing said speed control mechanism in pressure iluid communication with said outletconduit tourge said,

link toward said slow position when pressure fluid is discharged from said control valve, resilient means in said control mechanism for urging said link to said fast position, an inlet valve in said compressor for controlling the ow of uid through the compressor, pressure fluid actuating inlet valve mechanism in said compressor and connected to said inlet valve and also being in lluid communication with said outlet conduit, whereby said inlet valve is urged toward a closed position by discharge pressure from said control valve, a spring in said valve mechanism for urging it away from valve closing position, and resilient means acting on said inlet valve for urging the same toward closed position independently of said valve mechanism.

2. A device as recited in claim 1 further characterized in that said speed control mechanism has adjustable limit stops for maintaining the pressure range which is effective to operate said speed control mechanism within the pressure range which is effective to actuate said inlet valve mechanism.

3. A device as recited in claim 1 further characterized in that the connection between said pressure uid actuating inlet valve mechanism and said inlet valve includes an actuating rod having a free sliding t with said valve.

References Cited in the le of this patent UNITED STATES PATENTS 2,135,248 Aikman Nov. 1, 1938 2,629,536 Baker Feb. 24, 1953 2,661,893 Le Valley Dec. 8, 1953 2,704,631 Bancel Mar. 22, 1955 2,783,936 Kistler Mar. 5, 1957

Images