US3632231A

US3632231A - Suction pressure relieving system for a rotary vane compressor

Info

Publication number: US3632231A
Application number: US12546A
Authority: US
Inventors: Carl Bloom
Original assignee: Worthington Corp
Current assignee: Studebaker Worthington Inc; Atlas Copco Holyoke Inc
Priority date: 1970-02-19
Filing date: 1970-02-19
Publication date: 1972-01-04
Anticipated expiration: 1989-01-04

Abstract

A suction pressure relieving system for a rotary vane gas compressor which automatically establishes a safe startup pressure at the compressor inlet ports whenever the compressor is shut down.

Description

Emited States Patent Carl Bloom Springfield, Mass.

Feb. 19, 1970 Jan. 4, 1972 Worthington Compressor and Engine International Division of Worthington Corporation, a division of Worthington Corporation Holyoke, Mass.

Inventor Appl. No. Filed Patented Assignee SUCTION PRESSURE RELIEVING SYSTEM FOR A ROTARY VANE COMPRESSOR 9 Claims, 1 Drawing Fig.

US. Cl 417/295, 417/439, 417/540 Int. Cl F04c 29/08, F04b 49/00, F04b 39/00 Field of Search 417/295,

4-AIR lNLET [5 6] References Cited UNIT ED STATES PATENTS 2,516,291 7/1950 Bartholomew 417/20 2,613,026 10/1952 Banks 417/295 3,168,236 2/1965 Lamberton et a1. 417/295 3,186,631 6/1965 Lamberton et a1. 417/44 3,349,994 10/1967 Bloom 417/295 3,448,916 6/1969 Fraser 417/295 3,482,768 12/1969 Cirrincione et al. 417/295 Primary Examiner-Carlton R. Croyle Assistant Examiner-John J. Vrablik AttorneyFishman and Van Kirk ABSTRACT: A suction pressure relieving system for a rotary vane gas compressor which automatically establishes a safe startup pressure at the compressor inlet ports whenever the compressor is shut down.

Pmmmm 4:972 3.632.231

INVENTOR. CARL BLOOM M WZ%WM ATTORNEYS SUCTION PRESSURE RELIEVING SYSTEM FOR A ROTARY VANE COMPRESSOR BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the field of rotary vane gas compressors which have throttling valves in the compressor inlet conduits for controlling the suction pressure at the compressor inlet ports. Accordi g y. the general objects of the present invention are to provide novel and improved apparatus of such character.

2. Background of the Invention In rotary vane compressors where a throttling valve is used to control the compressor output as a function of the output pressure or load, it is frequently desirable to stop the compressor to reduce wear and power consumption whenever the demand or load on the compressor is zero for extended periods of time. In such situations, highpressure air in the compressor discharge system will leak back past the motionless vanes of the compressor into a confined portion of the inlet conduit. It is most probable that the suction pressure control valve in the compressor inlet will have been closed prior to compressor shutdown since it is the no load condition which causes the shutdown. In addition, the throttling valves used in such compressors often perform both the throttling function and a reverse flow checking function to prevent filters in the inlet line from being backwashed and to prevent large quantities of oil laden air from being expelled through the air inlet. As a consequence, when the compressor is shutdown, the compressed air which leaks back past the vanes will be captured within the throttled suction chamber and the compressor inlet.

Rotary vane compressors are designed with a specific compression ratio. It is quite possible that the compressor could be severely damaged if an attempt is made to start the compressor and further compress an abnormally highpressure gas existing at the compressor inlet ports. This highpressure condition can arise shortly after shutdown in compressors which have the suction pressure throttling valves due to the leakage past the motionless vanes. The pressure of this highpressure gas at the inlet ports would preclude restarting the compressor if a load demand occurs shortly after shutdown. It is therefore important that the pressure at the compressor inlet ports be relieved or bled down at least to a preselected maximum pressure which can be accommodated by the compressor. This maximum pressure will vary from one rotary compressor to another and will be defined as the maximum compressorstarting inlet pressurev It is also desirable that the static shutdown pressure which exists at both the inlet and discharge sides of the compressor after the highpressure gas has bled down to an equilibrium condition be as small as possible to minimize the initial driving torque required to start the compressor after shutdown.

It is important that the bleeding down of the highpressure gas through the compressor not occur too rapidly; otherwise, air dissolved in the oil on the highpressure side of the compressor will create excessive foam and flood the tanks and filters in the compressor discharge.

In order to reestablish the maximum discharge pressure as soon as possible after the compressor has been started up, it is desirable to minimize the volume of the discharge system which does bleed through the compressor into the inlet. This minimization also aids in minimizing the static shutdown pressure which will exist across the compressor in the equilibrium condition.

SUMMARY OF THE INVENTION The rotary vane gas compressor of this invention has an improved inlet system which provides a pressure at the inlet ports after the compressor has been shutdown which is no greater than the preselected maximum compressorstarting inlet pressure tolerated by the particular compressor in question.

The compressor is controlled in its output by means of a conventional suction control valve which is located in the compressor inlet conduit to restrict the amount of gas which reaches the compressor while it is running. This control valve is operated in response to the compressor load or discharge pressure in the receiver for the highpressure gas. Since the conventional suction control valve is both a throttling valve and a check valve, this valve will in all circumstances be closed when the highpressure gases leak back into the inlet suction chamber after shutdown.

In order to prevent the static shutdown pressure across the compressor from exceeding the preselected maximum, an auxiliary tank is connected into the suction chamber between the suction control valve and the actual compressor inlet ports.

In order to minimize the volume of highpressure gas which must be diffused into the suction chamber and auxiliary tank, a check valve is interposed in the compressor discharge manifold at a position close to the discharge port from the compressor itself. This check valve not only serves to minimize the volume of gas to be expanded but in addition maintains the oil tanks and demister tanks downstream of the compressor discharge manifold under the highpressure after shutdown. Maintaining these tanks at highpressure prevents oil foaming due to entrapped air and reduces the time necessary to reestablish maximum rated pressure output at the discharge ports after a new load demand occurs.

The compressor discharge system includes an oil tank from which lubricating fluid is fed back to the rotary compressor for lubrication. In order to prevent the oil from being forced under the highpressure in the discharge system into the rotary compressor, a flow control valve is provided in the filtered oil feed line to regulate the oil flow and prevent compressor flooding during shutdown.

Since the rate at which the highpressure gas will bleed back into the suction chamber is dependent upon other compressor design factors and therefore not readily controllable, a regulated pressure bleeding conduit which bypasses the compressor itself interconnects the highpressure discharge manifold with the inlet manifold. A valve interposed in this bleed con duit can be shut off during compressor operation and regulated during compressor shutdown for the most desirable bleed down rate in view of the oilfoaming problem within the compressor and discharge manifold itself.

If desired, a pressure switch interlocking with the compressor startup system may be employed to prevent inadvertent starting when for any reason the pressure at the inlet ports is not below the maximum compressorstarting inlet pressure.

BRIEF DESCRIPTION OF THE DRAWING The drawing shows my sucn'on pressure relieving system which provides a safe compressor starting inlet pressure for a rotary vane compressor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference to the drawing shows the inlet pressure control system including my improved inlet for relieving the compressor starting inlet pressure.

The rotary vane compressor is generally designated by the numeral 10. The compressor 10 has an inlet 12 and a discharge manifold 14 which leads to a discharge receiver 16. The receiver performs the function of storing the high-pressure air until it is needed for operating an air hammer or other pneumatic device.

Inlet air which is to be processed by the compressor enters the air inlet 12 and first passes through a filter 18. After the air has been filtered it passes to a suction control system which includes a suction control valve 20 and a suction chamber 22 connected to the rotary compressor adjacent the inlet ports.

The control valve 20 is a conventional suction control valve which includes a springbiased, diaphragmoperated valve stem 24 and a valve plate 26 slidably mounted on the stem 24.

Such valves are well known in the art. The function of such a valve is to regulate the quantity of air which passes to the compressor as a function of the load or discharge pressure from the receiver 16. In order to provide the appropriate pressure control signal for operating the valve 20, a control pressure conduit 28 is connected from the discharge receiver 16 to the valve 20 below diaphragm 29 to control the position of the springbiased valve stem 24. A pressure regular 27 is included in the conduit 28 to adjust the pressure which operates the valve 20.

Connected to the suction chamber 22 by means of conduit 30 is an auxiliary tank 32 which performs one of the principal functions of my invention. The tank 32 connects directly into the suction chamber 22 and is carefully matched with the volume of the chamber 22 and the compressor system to operate as described below.

A pressure sensing switch 34 is also connected to the suction chamber 22. The pressure switch may be interconnected with a compressorstarting system such as a motor starter which starts the driving motor for the compressor. The pressure switch 34 is sensitive to the inlet or suction chamber pressure and prevents starting of the compressor unless the inlet pressure is below the maximum permitted compressorstarting inlet pressure. The pressure switch therefore is a safety device supplementing my improved inlet pressure relieving system.

Highpressure air leaving the compressor 10 through discharge manifold 14 first passes through a check valve 36 which prevents reverse flow of the compressed air in a large portion of the discharge system. The compressed air then passes into an oil tank 38 where the bulk of the lubricating oil carried by the highpressure air is deposited. From the oil tank the high-pressure air is transmitted to a demister tank 42 where the remaining oil is separated from the air. From the demister tank 42 the oilfree air is transmitted through a second check valve 44 to the discharge receiver 16 for use as needed. Check valve 44 maintains pressure in receiver 16 during compressor shutdown The lubricating system for the compressor 10 includes the oil tank 38, the oil filter 40, the oil feed line 46, and the oil flow valve 48. The compressed air in the oil tank 38 will force oil through the filter 40 into conduit 46 and the compressor 10. Valve 48 is adjusted to control the rate of oil flow to the compressor 10 as needed for its efficient operation and cuts off flow at shutdown to prevent the oil from flooding the compressor.

In one embodiment of my invention I include a gas pressure bleed line 50 connected to the discharge manifold 14 and the suction chamber 22. A bleed valve 52 incorporated in the line 50 is used to adjust the rate at which highpressure gas is permittedto flow back into the suction chamber 22 after the compressor 10 has been shutdown. Since the rate at which highpressure air bleeds through the compressor depends on clearances established for efficient gas compression and, therefore, cannot be independently designed into the compressor, the bleed line 50 offers a convenient alternative. During normal compressor operation the valve 52 would be closed so that no flow in line 50 will interfere with the regulation of suction chamber pressure by control valve 20.

It is an important feature of my invention that the inlet control system relieve the suction chamber pressure when the compressor is shutdown at the noload condition. The inlet system is designed to reduce the inlet pressure to a prescribed value and at a rage which prevents foaming of the oil entrained in the highpressure air.

When the rotation of the compressor vanes is stopped, highpressure air will exist in the compressor itself as well as in the portion of the discharge manifold 14 between the compressor 10 and check valve 36. Since there is a pressure differential across the compressor 10 immediately after shutdown, the highpressure air will tend to leak around the vanes and rotor of the compressor into the suction chamber 22. A controlled leakage rate may be established through bleed line 50 with valve 52. The leakage will be prevented from backflowing through the filter l8 and air inlet 12 by means of the suction control valve 20. Valve 20 will most likely have been closed due to the noload condition immediately prior to compressor shutdown and even if the valve has not been closed by the load condition, the flowchecking function of valve 20 will prevent undesired backwashing of filter l8 and expulsion of the oil laden air at the inlet 12.

Without the improved inlet system, the equilibrium pressure or static shutdown pressure generated by the bleed back of highpressure gas could prevent compressor startup until leakage through the compressor seals and the suction valve eventually drops the inlet pressure to an acceptable level. This delay in restarting the compressor may severely hamper its utility particularly where a new demand from the receiver 16 arises shortly after the compressor is shut down.

To prevent an undesirably long delay in restarting the compressor, the auxiliary tank 32 is calibrated with the suction chamber 22, compressor 10 and manifold 14 to increase the total confined gas volume to a value which will expand the highpressure air in the discharge manifold 14 down to the tolerable maximum compressorstarting inlet pressure, for example, lO p.s.i.g. The tolerable pressure will vary from one compressor to another depending on its capacity to withstand high discharge pressures.

In order to further reduce the task of expansion performed by the auxiliary tank 32, the check valve 36 is located in the discharge manifold 14 at a position which will minimize the initial volume of highpressure gas which must be expanded into the suction chamber 22 and an auxiliary tank 32. The check valve 36 additionally maintains the oil tank 38 and the remainder of the discharge system under the high pressure. Two advantages are readily apparent. First, lubricating oil in tank 38, line 46 and the remainder of the discharge system will not foam due to entrained air as the discharge manifold 14 is bled down. Second, the total volume of the discharge system which must be pumped up to discharge pressure when the compressor is restarted is minimized and consequently the time necessary for the compressor 10 to reestablish its rated discharge pressure is minimized.

The rate at which the small volume of air in discharge manifold 14 is brought to equilibrium across the compressor 10 can be readily controlled by the adjustment of bypass line 52. The controlled rate is desirable to prevent sudden equalization of the pressures across the compressor and the resulting foaming of oilladen air in discharge manifold 14.

It will be understood that the precise system disclosed can have many forms without departing from the scope of the invention. For example, as pointed out above, the control bleed line 50 is not essential to the system. In addition, more than one auxiliary tank 32 may be connected to the line 30 so that the total volume of the suction chamber 22 and the tanks 32 will establish the desired static shutdown pressure. in this respect, however, it should be noted that the added, calibrated volumes of the auxiliary tank 32 will reduce the suction pressure response at the inlet ports of the compressor 10 to the regulation of suction control valve 20. It is therefore preferred that the total volume of the auxiliary tanks 32 be calibrated in conjunction with the suction chamber 22 to perform the inlet pressure relieving function without significantly interfering with the throttling function of the suction control valve 20.

What is claimed is:

1. In a rotary vane gas compressor system including an inlet suction control valve, a rotary vane compressor having inlet and discharge manifolds, and a compressed gas receiver, the improvements comprising:

valve means interposed between the compressed gas receiver and the compressor discharge manifold for preventing flow of compressed gas in the receiver back into the rotary compressor; and

auxiliary chamber means connected to the rotary compressor inlet manifold and having a preselected minimum volume for reducing the static shutdown pressure across the rotary compressor to a value not greater than a maximum startup inlet pressure limit.

2. The improvements of claim 1 further including:

a oil demister tank connected to the compressed gas receiver upstream in the direction of normal gas flow from the receiver and downstream with respect to the valve means.

3. The improvements of claim 1 further including:

an oil reservoir interposed between the valve means and the compressed gas receiver;

an oil feed conduit connecting the oil reservoir with the rotary compressor; and

an oil flow regulating valve interposed in the oil feed conduit for regulating the flow of oil from the reservoir to the rotary compressor.

4. The improvements of claim 3 still further including:

an oil filter located in the oil feed conduit between the reservoir and the oil flow regulating valve.

5. An automatic inlet pressure relieving apparatus for a retary pneumatic compressor, said compressor having an inlet, a discharge manifold and a highpressure gas discharge conduit connecting said discharge manifold to a highpressure gas 2 receiver, said pressurerelieving apparatus comprising:

suction control throttle valve means connected upstream of the gas inlet of the rotary compressor;

check valve means connected in the highpressure gas discharge conduit between the highpressure gas receiver 25 and the compressor discharge manifold for checking flow from the receiver back to the compressor; and

an auxiliary suction pressure tank connected to the gas inlet downstream of the throttle valve means in the direction of gas flow through the throttle valve, the tank having an internal gas volume contiguous with the internal volumes of the throttle valve means, the gas inlet, the rotary compressor and the gas discharge path between the compressor and check valve means, said tank providing a static shutdown pressure at the gas inlet no greater than a preselected maximum pressure.

6. The pressure-relieving apparatus of claim 5 further including:

a pressurebleeding conduit connected at one end to the highpressure gas discharge between the rotary compres- 40 sor and the check valve means and at the opposite end to the gas inlet of the compressor; and v a shutoff valve positioned in the pressurebleeding conduit between the ends of the conduit whereby the bleeding of the higher pressure discharge gas through the conduit to the compressor inlet can be shutoff.

7. A suction control inlet for a rotary air compressor having an inlet and discharge manifold means including a valve for inhibiting reversed flow of the compressed air comprising:

an inlet conduit defining a passage for admitting a flow of ambient air;

inlet check valve means located in the inlet conduit and oriented to transmit the airflow toward the rotary compressor and prevent reverse flow through the inlet conduit;

suction control means connected with the check valve means and responsive to the load on the compressor for regulating the inlet air pressure at the rotary compressor; auxiliary chamber means operatively connected between the suction control means and the rotary compressor, the chamber means having a chamber volume commensurate with the remaining air volume between the inlet check valve means and the flow inhibiting valve in the discharge manifold means whereby the volume of compressed air in the compressor and discharge manifold at shutdown will be expanded into the auxiliary chamber means volume and remaining volume at a pressure no greater then a prescribed maximum compressorstarting inlet pressure. 8. The apparatus of claim 7 further including: an air filter positioned in the inlet conduit at a location upstream in the direction of inlet airflow from the inlet check valve means whereby the check valve means prevents back washing of the air filter.

9. The a paratus of claim 7 wherein: the auxi iary chamber means includes at least one tank connected to the compressor inlet downstream of the suction control means and having an internal volume calibrated for expansion of the volume of compressed air below the maximum compressorstarting inlet pressure.

Claims

1. In a rotary vane gas compressor system including an inlet suction control valve, a rotary vane compressor having inlet and discharge manifolds, and a compressed gas receiver, the improvements comprising: valve means interposed between the compressed gas receiver and the compressor discharge manifold for preventing flow of compressed gas in the receiver back into the rotary compressor; and auxiliary chamber means connected to the rotary compressor inlet manifold and having a preselected minimum volume for reducing the static shutdown pressure across the rotary compressor to a value not greater than a maximum startup inlet pressure limit.

2. The improvements of claim 1 further including: a oil demister tank connected to the compressed gas receiver upstream in the direction of normal gas flow from the receiver and downstream with respect to the valve means.

3. The improvements of claim 1 further including: an oil reservoir interposed between the valve means and the compressed gas receiver; an oil feed conduit connecting the oil reservoir with the rotary compressor; and an oil flow regulating valve interposed in the oil feed conduit for regulating the flow of oil from the reservoir to the rotary compressor.

4. The improvements of claim 3 still further including: an oil filter located in the oil feed conduit between the reservoir and the oil flow regulating valve.

5. An automatic inlet pressure relieving apparatus for a rotary pneumatic compressor, said compressor having an inlet, a discharge manifold and a high-pressure gas discharge conduit connecting said discharge manifold to a high-pressure gas receiver, said pressure-relieving apparatus comprising: suction control throttle valve means connected upstream of the gas inlet of the rotary compressor; check valve means connected in the high-pressure gas discharge conduit between the high-pressure gas receiver and the compressor discharge manifold for checking flow from the receiver back to the compressor; and an auxiliary suction pressure tank connected to the gas inlet downstream of the throttle valve means in the direction of gas flow through the throttle valve, the tank having an internal gas volume contiguous with the internal volumes of the throttle valve means, the gas inlet, the rotary compressor and the gas discharge path between the compressor and check valve means, said tank providing a static shutdown pressure at the gas inlet no greater than a preselected maximum pressure.

6. The pressure-relieving apparatus of claim 5 further including: a pressure-bleeding conduit connected at one end to the high-pressure gas discharge between the rotary compressor and the check valve means and at the opposite end to the gas inlet of the compressor; and a shutoff valve positioned in the pressure-bleeding conduit between the ends of the conduit whereby the bleeding of the higher pressure discharge gas through the conduit to the compressor inlet can be shutoff.

7. A suction control inlet for a rotary air compressor having an inlet and discharge manifold means including a valve for inhibiting reversed flow of the compressed air comprising: an inlet conduit defining a passage for admitting a flow of ambient air; inlet check valve means located in the inlet conduit and oriented to transmit the airflow toward the rotary compressor and prEvent reverse flow through the inlet conduit; suction control means connected with the check valve means and responsive to the load on the compressor for regulating the inlet air pressure at the rotary compressor; auxiliary chamber means operatively connected between the suction control means and the rotary compressor, the chamber means having a chamber volume commensurate with the remaining air volume between the inlet check valve means and the flow inhibiting valve in the discharge manifold means whereby the volume of compressed air in the compressor and discharge manifold at shutdown will be expanded into the auxiliary chamber means volume and remaining volume at a pressure no greater than a prescribed maximum compressor-starting inlet pressure.

8. The apparatus of claim 7 further including: an air filter positioned in the inlet conduit at a location upstream in the direction of inlet air flow from the inlet check valve means whereby the check valve means prevents back washing of the air filter.

9. The apparatus of claim 7 wherein: the auxiliary chamber means includes at least one tank connected to the compressor inlet downstream of the suction control means and having an internal volume calibrated for expansion of the volume of compressed air below the maximum compressor-starting inlet pressure.