US3482768A - Compressor control system - Google Patents

Description

Dec. 9, 1969 e. #:IRRINGONE ET AL 3,482,768

COMPRESSOR CONTROL SYSTEM Filed Feb. 28, 1968 ROBE/P7 R ANDERSON INVENTOR.

Bu /av, f ATTORNEY United States Patent Ofliee 3,482,768 Patented Dec. 9, 1969 3,482,768 COMPRESSOR CONTROL SYSTEM GilbertCirrincione and Robert R. Anderson, Quincy, Ill., assignors to Gardner-Denver Company, a corporation of Delaware Filed Feb. 28, 1968, Ser. No. 709,110 Int. Cl. F04c 27/02, 29/02, 29/04 U.S. Cl. 230205 Claims ABSTRACT OF THE DISCLOSURE An unloading system for rotary liquid injected compressors including a self-regulating flow control valve associated with the liquid injection supply system and operable to restrict the flow of liquid to the compressor while the compressor is running unloaded. Excess liquid is purged from the liquid injection system by venting compressed gas into the compressor liquid injection gallery. The self-regulating valve provides substantially reduced flow of liquid during the unloaded running condition and together with the compressed gas purging action eliminates the vibration and noise caused by high liquid injection rates, and prevents choking or flooding of the compressor.

BACKGROUND OF THE INVENTION Conventional positive displacement rotary gas compressor units include a class of machines in which a liquid is continually injected into the compression chamber of the compressor in large quantities for cooling the gas being compressed, as well as for lubricating and gas tight sealing the working mechanism of the compressor. These compressor units usually include a combination compressed gas receiver-liquid reservoir tank located downstream of the compressor discharge passage where separation of the liquid from the compressed gas is attained. The liquid .is usually recirculated by .-a metering pump via attendant devices such as filters and heat exchangers to provide continuous injection into the compressor.

Recent developments in the art of rotary liquid injected compressors have provided, in many cases, for the elimination of the aforementioned metering pumps and instead liquid circulation is provided -by utilizing the pressure differential between the liquid reservoir ,tank and the injection ports in the compressor; the latter desirably being near the compressor inlet. Also in the art of liquid injected compressors, capacity control systems have been developed which combine throttling the compressor inlet by suitable valve means with venting the compressed gas receiver-oil reservoir tankto atmospheric pressure and thereby reducing the power consumption of the compressor when running unloaded. In compressors operating under these conditions, portions of the compression chamber near the inlet and interior areas of the compressor communicating therewith become rapidly evacuated to a near total vacuum as the pumping action of the compressor displaces gas and liquid out through the discharge line. v

An example of this type of system is disclosed in U.S. Patent No. 2,234,469 issued to Burns Dick. In the Dick patent a combination air receiver-lubricating oil reservoir tank is vented to atmosphere through a valve operated in conjunction with a compressor inlet throttling valve. The Dick patent also discloses that the reduced pressure differential between the oil reservoir and the point of oil injection into the compressor during unloaded operation provides for a reduced oil injection rate to prevent flooding :or choking the compressor.

In the aforedescribed type of compressor system, even though the pressure differential between the receiverreservoir in the compressor liquid injection port is decreased somewhat during unloaded operation, excessive amounts of liquid tend to collect in the evacuated compression chamber of the compressor causing undue work by the compressor in pumping the liquid through the compressor and into the receiver-reservoir, and often resulting in high vibration and noise levels due to flooding or choking of the interior of the compressor. It has been established that a suitably high liquid injection rate for the loaded running condition and a suitably low liquid injection rate for the unloaded running condition cannot be attained by simply providing a fixed resistance to flow in the form of an orifice or a predetermined length of supply conduit.

Accordingly it is desirable to provide suitable means for controlling the flow of liquid to the compressor during periods of unloaded running to restrict the injection rate to an amount sufficient only for cooling and lubricating the moving parts.

SUMMARY OF THE INVENTION The invention resides in the provision in a control system for positive displacement rotary compressors of the liquid injected type of a flow control valve for restricting the rate of liquid injected into the compressor when run ning in the unloaded condition.

By restricting the flow of liquid to the compressor when the interior compression spaces have been evacuated during unloaded operation unwanted accumulation and flooding of the compressor by the injection liquid is prevented and only an amount of liquid necessary for cooling and lubricating the moving parts and for cooling minute quantities of gas leaking into the compression chamber is permitted to flow through the machine.

The invention also provides for a liquid flow control valve that is self-regulating to permit maximum flow of injection liquid during periods of loaded operation of the compressor and operable to limit the amount of liquid injected during periods of unloaded operation to a desired proportional amount of the loaded injection rate. This proportional flow rate is achieved by a spring loaded valve element which reacts to a predetermined pressure in the liquid injection line to the compressor during loaded operation to permit suitable injection rates for efiicient operation. During unloaded operation, however, the pressure on the valve is insuflicient to prevent the valve from closing whereby flow of liquid to the compressor under such conditions is metered by a properly sized orifice located in the valve element.

The invention also provides for purging excess oil from the compressor interior by utilizing the venting of compressed gas from the compressor system at the onset of unloaded operation to rapidly displace excess oil remaining in the system downstream of the flow control valve.

By providing a self-regulating valve simple and compact in construction and reliable in operation, in combination with compressed gas purging of excess oil from the compressor, liquid injected compressor units of the type discussed herein may be operated more etficiently than heretofore realized.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic illustration of a liquid injected gas compressor system embodying the present invention.

FIG. '2 is a sectional view of a portion of a typical rotary liquid injected compressor casing illustrating details of the self-regulating liquid flow control valve.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The schematic illustration of FIG. 1 represents a compressor system characterized by a positive displacement liquid injected rotary compressor. C mpressors of this type are generally categorized as being of either the sliding vane or helical screw design although other types are known and used to a lesser degree in the art. Such compressors are widely used for industrial compressed air systems, in the construction industry, and various applications for compressing gases other than air. For most applications the injection liquid is a lightweight mineral oil, although special systems have used water, condensed vapors, and various other liquids. For the purpose of this disclosure, the compressor system of FIG. 1 will be considered to be that of an inddustrial plant air compressor unit having an oil injected, helical screw compressor generally designated by numeral driven by an electric motor 12. The compressor 10 is equipped with an inlet throttling valve 14 actuated by a valve operator 16. An inlet air cleaner 18 is shown mounted upstream of the valve 14. Compressed air and oil are discharged from the compressor 10 through a discharge line 20 to a combined air receiver-oil reservoir tank 22 which may contain suitable means for separating from the compressed air virtually all liquid such as the oil and condensed water vapor. The liquid free air then flows through conduit 24 and check valve 26 to a compressed air storage tank 28. The valve 30 provides control over compressed air flowing from the tank 28 to the end usage. In many compressed air distribution systems the tank 28 may be eliminated since the network of piping making up the distribution system serves as adequate storage capacity for the compressed air.

The compressor oil injection system includes the com bination air receiver-oil reservoir tank 22 serving as a source of injection oil from which extends an oil supply line 32 leading to a filter 34. A continuing oil supply line 36 leads to a heat exchanger 38 and from that com ponent line 40 connects to a flow control valve housing 42 located on the compressor casing 44.

Also illustrated in the schematic of FIG. 1 are the c ntrol components of the compressor system which include a conduit 46 in communication with the compressed air storage tank 28 and a pilot or self-actuated valve 48 which is responsive to a predetermined pressure in the conduit 46 to open and admit pressure air to the conduit 50 which is in communication with the valve operator 16. Also connected to the conduit 50 is a pressure switch 52 whose purpose will be discussed herein.

In communication with the receiver-reservoir tank 22 is a vent conduit 54 leading to a normally open solenoid valve 56. The valve 56 is electrically connected to the pressure switch 52 by suitable means (not shown) and is controlled to be closed when energized, that is when the switch 52 is closed. Downstream of the valve 56 a conduit 58 leads to an exhaust muffler 60 vented to atmosphere and a secondary conduit 62 leads through a flow restrictor 64 and a check valve 66 to the flow control valve housing 42.

Referring to FIG. 2 the flow control valve housing 42 is illustrated fastened to the compressor casing 44 by suitable means, not shown, and having an interior portion 68 opening into the compressor oil injection gallery 70. Communicating with the gallery 70 is passage .72 which leads to various locations within the compressor which require lubrication and cooling such as bearings, drive gears and seals. As shown in FIG. 2, the housing 42 comprises a cover for liquid injection gallery 70. Also in communication with the gallery 70 are the main oil injection ports 74 which communicate directly with the compression chamber of the compressor. Secondary oil injection ports 76 receive drainage oil from the aforementioned bearings, etc., via passages 78 opening into cavities 80.

The oil injection flow control valve designated in its entirety by 82 comprises a plug member 84 having a hollow interior 85 partially threaded for receiving the conduit 40. The plug member 84 is threadedly disposed in the housing 42 and forms a seat for a valve closure plate 86 which is biased to the closed position by a coil spring 88. A bypass orifice 90 in the valve plate 86 is sized to permit a predetermined flow of oil into the gallery when the valve is closed. A spring and closure plate retainer 92 is suitably secured to the plug 84 by pins 94 which also serve to guide the closure plate. A plug 96 is threadedly disposed in the housing 42 also, and connected thereto is the secondary vent line 62 which communicates with the interior 68 of the valve housing 42 via the passage 98.

The function of the oil flow control valve and the compressor system in general can best be explained by a discussion of the operation of the system. As previously mentioned the compressor system shown is typical of the type provided for industrial plants for compressing atmospheric air to nominal pressures in the range of 100 to p.s.i.g. depending on plant requirements.

In operation, the system with the motor deenergized and no pressure air in the tank 28 will find the pilot valve 48 closed, the throttling valve 14 is also lightly biased to be closed, and the solenoid valve 56 open. The compressor unit is started by closing a switch on a motor starter unit, not shown, to energize the motor. The pressure switch 52, also suitably electrically connected to the motor starter unit and being in the closed position, will permit energization of the solenoid valve 56 to close the same. As the compressor accelerates to running speed a near total vacuum is momentarily created in the compressor inlet creating a pressure differential across the compressor throttling valve 14 sufficient to open the valve and admit air to the compressor. Ordinarily the valve 30 is closed or nearly closed prior to compressor startup so that pres sure in the receiver-reservoir tank 22 and the storage tank 28 builds up rapidly and oil commences to flow from the tank 22 through the injection supply system consisting of the conduit 32, filter 34, conduit 36, heat exchanger 38, and conduit 40 to the fiow control valve 82. In response to the substantial pressure differential between the now pressurized tank 22 and the interior 68 of the control valve housing, and oil injection gallery 70, the flow control valve closure plate 86 will be forced fully open to provide full oil flow to the compressor 10. The compressor system is now running with full oil and inlet air flow to supply compressed air to the end usage.

As demand for compressed air downstream of the service valve 30 decreases pressure in the storage tank 28 and receiver-reservoir 22 will rise to a preset unload value sensed by the pilot valve 48, for example, 100 p.s.i.g. When this condition is reached the self-actuating pilot valve will commence the unloading cycle by opening to admit pressure air to the conduit 50 to be sensed by the pressure switch 52 and the inlet valve operator 16 whereupon, simultaneously, the switch will open to deenergize the solenoid valve 56 opening the same, and the operator 16 will actuate to close the compressor inlet valve 14 shutting ofi the supply of inlet air to the compressor.

Opening the solenoid valve 56 will result in the venting of the receiver-reservoir tank 22 to atmosphere through the vent conduit 58 and mufiier 60. The check valve 26 prevents back flow of compressed air from the storage tank 28. During the venting phase of unloading a quantity of pressure air will flow through the secondary vent conduit 62 and into the flow control housing 42 to purge or scavenge excess oil present therein and in the injection gallery 70 by forcing the oil through the injection ports 74. As the pressure in the receiver-reservoir tank is reduced to atmospheric conditions, the interior of the compressor in and near the inlet will also be evacuated to a near total vacuum caused by the pumping action of the compressor. This vacuum condition will also exist in the interior of the valve housing and the oil injection gallery due to the fact that the injection ports 74 and 76 communicate with the compression chamber in the vicinity of the compressor inlet.

When the steady state unloaded condition is reached the pressure difierential across the flow control valve is essentially one atmosphere and the closure plate 86 urged by the spring 88 will close permitting only enough oil to fioW to the compressor as determined by the bypass orifice 90 in the closure plate. Thus, during unloaded operation, flooding of the compressor interior with oil is prevented and vibration and noise resulting from such flooding is eliminated. As will be noted in the drawing, the oil flow control valve 82 is desirably located as close to the compressor as is practical, the purpose being in this respect to minimize the quantity of excess oil required to be purged between the flow control valve and the interior of the compressor at the onset of the unloading cycle.

During unloaded operation, only a small percentage of the loaded running condition oil fiow is required to adequately cool and lubricate the moving parts in the compressor. It has been determined that oil flows during unloaded operation on the order of 5 to 10 percent of loaded operating oil flow rates have been found to be suitable. For example, a typical oil injected helical screw compressor rated at 900 cubic feet per minute air capacity operates with an oil injection rate loaded of approximately 85 gallons per minute but optimally requires only 5 gallons per minute when running at the same speed unloaded. Power requirements to drive the compressor during the unloaded condition are also reduced with regulated oil flow. It has been established that running unloaded with maximum oil flow requires approximately percent of full load power. However, with oil flow reduced to the percentages stated herein, power requirements are on the order of 10 to 12 percent of full load power,

Also, during unloaded operation, a small quantity of air :will flow from the reservoir tank 22, through the vent conduits 58, and the secondary vent conduit 62, to mix with the reduced quantity of oil flowing through the interior 68 of the flow control valve housing 42 and provide an atomized oil-air mixture which further reduces vibration and noise in the compressor. The oil-air mixture is, of course, eventually pumped through the compressor and into the reservoir tank via the discharge line 20. The flow restrictor 64 limits the quantity of air fiowing to the compressor under these conditions to an amount inconsequential to compressor power demand.

The resumption or increase in pressure air demand will cause the pressure in the storage tank 28 to drop and upon reaching a preset minimum the pilot valve 48 will shift to close and vent the conduit 50. The compressor will then resume loaded operation as the switch 52 closes to energize the solenoid valve 56 to prevent venting of the receiver-reservoir tank, and the compressor inlet valve 14 will open to permit full inlet air flow to the compressor. Pressure increase in the receiver-reservoir tank 22 will again force full oil flow as the flow control valve 82 opens in response to the increased pressure differential.

From the above description of the preferred operating characteristics and arrangement of structure of the subject control system, it will be obvious that minor changes in the system may be made without departing from the scope of the invention. For example, the flow control valve 82 may be located at other points in the injection liqirid supply system between the receiver-reservoir tank 22 and the compressor 10 with, however, less desirable results. Also, in some systems it is desirable to include a metering pump in the liquid supply line rather than depending entirely on the pressure differential between the liquid reservoir and the compressor. The pump may be advantageously driven by an auxiliary drive shaft On the compressor or by separate drive means. In such a case it is desirable to position the oil flow control valve upstream of the pump so that the valve may still be operative in the unloaded condition to provide for a reduced oil flow rate. Moreover, the system disclosed need not be limited to industrial air compressors, but could be applied to many applications involving liquid injected rotary compressors.

What is claimed is: 1. In a gas compressor system: rotary gas compressor means having gas inlet and discharge means and liquid injection port means; a liquid source havnig pressurized and vented conditions; supply means communicating liquid from said source to said injection port means; and the improvement comprising:

control valve means in circuit with said supply means operable to provide maximum liquid flow to said injection port means when said source is pressurized and regulated liquid flow when said source is vented, said valve means including flow regulating bypass means eflective when said source is vented to limit liquid flow. 2. The improvement set forth in claim 1 wherein: said source of liquid comprises a compressed gas-liquid reservoir tank connected to said compressor discharge means; said reservoir tank operable to be in a gas pressurized condition and in a vented condition thereby establishing a first pressure differential and a reduced pressure differential, respectively, between said reservoir tank and said liquid injection port means in said compressor; and said flow control valve comprises a closure member responsive to said first pressure differential acting thereon to open thereby providing said maximum liquid. flow and said closure member operative to close thereby providing regulated liquid flow in response to said reduced pressure differential acting thereon. 3. The invention according to claim 2 wherein: said flow control valve includes resilient means acting on said closure member to bias said closure member to close. 4. The improvement set forth in claim 2, wherein: said bypass means in said flow control valve comprises orifice means in said closure member. 5. The improvement set forth in claim 2 wherein: said fiow control valve includes valve housing means, said housing means being located substantially on said compresor means and adjacent said liquid injection port means in said compressor whereby the volume of liquid in said conduit means between said flow control valve and said liquid injection port means is minimized. 6. The improvement set forth in claim 2 together with:

liquid purging means comprising conduit means in communication with said compressor and Said liquid reservoir tank, said purging means being operable to conduct pressure gas from said reservoir tank to said compressor for purging excess liquid from within said compressor. 7. The improvement set forth in claim 6 wherein: said purging conduit means is in communication with said liquid conduit means between said flow control valve and said liquid injection port means in said compressor. 8. In a gas compressor system: rotary gas compressor means having gas inlet and discharge means and liquid injection port means; combined gas receiver and liquid reservoir means operably connected to said compressor for receiving compressed gas therefrom and operable to be in a gas pressurized condition and a vented condition; liquid supply means connecting said reservoir with said injection port means, said supply means including gallery means on said compressor in communication with said liquid injection port means, said gallery means having a cover member; and the improvement comprising:

liquid purging means comprising conduit means connecting said gas receiver and said gallery means, said liquid purging means including valve means in circuit with said conduit means and operable to vent said receiver-reservoir means to said conduit means whereby in response to venting said receiver-reservoir means liquid is purged directly from said gallery means.

9. In a gas compressor system:

rotary gas compressor means having gas inlet and discharge means and liquid injection port means, said compressor means being operable to be in a loaded condition and an unloaded condition;

a liquid source having a pressurized condition when said compressor is loaded and a vented condition when said compressor is unloaded;

liquid supply means communicating liquid from said source to said injection port means; and the improvement comprising:

control valve means in circuit with said supply means for regulating liquid flow to said injection port means when said source is vented.

10. In a gas compressor system:

rotary gas compressor means having gas inlet and discharge means and liquid injection port means;

liquid injection means comprising a source of liquid and liquid supply means connecting said source with said injection port means;

flow control means in circuit with said liquid supply means;

compressed gas receiver means operably connected to said compressor for receiving compressed gas therefrom; and the improvement comprising:

liquid purging means comprising conduit means connecting said gas receiver means with said liquid supply means between said fiow control means and said injection port means, said purging means being operable to vent compressed gas from said receiver means to said liquid supply means for purging liquid therefrom.

References Cited UNITED STATES PATENTS ROBERT M. WALKER, Primary Examiner US. Cl. X.R.

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