Apparatus and method for electronically controlling inlet flow and preventing backflow in a compressor

Abstract: An apparatus for electronically controlling the flow of low pressure gas to a compressor (12) and preventing backflow from the compressor, the apparatus including a housing (14) in fluid communication with the compressor, where the housing has a chamber (34), a housing inlet (16) for receiving a low pressure gas and a housing discharge port (20) for flowing the low pressure gas to the compressor and through which backflow gas flows from the compressor. A valve member (70) having a contact end (73) is movable within the chamber along a predetermined path. The apparatus also includes a drive (80) for moving an actuator (82) along an axis (53). The actuator has an extension (84) with an end adapted to abut the contact end of the valve member thereby to move the valve member along the path towards the housing inlet. The valve member is movable along the path and away from the inlet, when the actuator is retracted, by the flow of low pressure gas through the inlet. Upon compressor shutdown, the back pressure moves the valve member to a substantially occluding position relative to the inlet position to prevent backflow from flowing outward from the compressor.

Description: This invention generally relates to a compressor inlet valve, and more particularly to a compressor inlet valve for electronically controlling inlet gas flow and preventing backflow through the compressor inlet. In order to control the throughput or capacity of a compressor, a compressor typically includes an inlet valve which regulates the compressor capacity. One type of inlet valve is commonly referred to as an unloader valve because the valve is used to load and unload the compressor. The compressor is loaded when the inlet valve is open permitting fluid, such as air, to flow through the compressor inlet. The compressor is unloaded when the valve is closed thereby "choking" or blocking the flow of fluid through the compressor inlet. Unloader valves may be opened and closed pneumatically. Pneumatically controlled unloader valves require a regulation air system for operation. Although the pneumatically controlled unloader valves have operated with varying degrees of success, there are problems associated with such valves. When the compressor is operated in temperatures that are below freezing, the regulation air system may freeze and render the inlet valve inoperable. Additionally, the regulation air system requires regular maintenance in order to ensure that the air system can effectively actuate the unloader valve during compressor operation. This regularly conducted maintenance can be time consuming and may render the compressor inoperable when it is being performed. Unloader valves may also be opened and closed hydraulically. Hydraulic unloader valves frequently leak hydraulic fluid and require replacement of parts, such as diaphragms, for example. A problem associated with compressors, especially oil-flooded screw compressors, is backflow through the compressor inlet. Such backflow is comprised of a combination of a gas, such as air, and oil. Backflow occurs when the compressor is stopped while the compressor system is pressurized. It is undesirable to permit backflow to be released into the environment because of the loss of oil from the system and associated contamination of the environment. One conventional way of preventing backflow is by inserting check valves in the air service and oil injection lines. Conventional check valves are spring actuated to permit unidirectional flow of compressed gas or oil, away from the compressor. In this way, backflow is prevented by the check valves. Although current check valves are effective in preventing backflow, it would be more desirable to prevent backflow without introducing additional discrete valves into the system. The addition of the discrete check valves increases the cost and complexity of the compressor. In hydraulically and pneumatically operated unloader valves, the backflow may be used to close the unloader inlet. However, the tendency to freeze, problems with leaking oil and hydraulic fluid and required maintenance make hydraulically and pneumatically operated unloaders undesirable. Electronically operated inlet valves typically include a stepper motor that is connected to a disc or piston that is movable by the motor. A pressure sensor measures compressor discharge pressure, generates a signal in response to the measured pressure and communicates the signal to a controller. In response to the signal generated by the sensor, the controller calculates the distance that the disc or piston needs to be moved to obtain the desired discharge pressure and rotates the stepper motor in short, discrete angular movements to thereby move the disc or piston the calculated distance. Typically, the disc or piston when fully closed, does not seal the inlet well enough to prevent backflow of oil. To date, compressors with electrically actuated inlet valves do not seal against backflow and require that a discrete check valve be inserted in a compressed air service line, typically located downstream from the compressor discharge port along with another check valve, known in the art as an oil stop valve, located in an oil injection line. These valves increase the cost and complexity of the compressor. US-A-4 406 589 (corresponding to DE-A-31 06 980) discloses an example of a compressor with apparatus to control flow of low pressure gas and to prevent backflow in accordance with the preamble of claim 1. According to one aspect of the present invention, there is provided a an apparatus for controlling the flow of low pressure gas to a compressor and preventing backflow of compressed gas from the compressor, the apparatus comprising a housing for fluid communication with the compressor, said housing having a chamber, a housing inlet for receiving low pressure gas, and a housing discharge port for allowing said low pressure gas to flow to said compressor and through which backflow flows, in use, from said compressor, and a valve member having a valve stem connected to said valve member and having a contact end, said valve member being movable within said chamber towards and away from said inlet along a common axis, said valve member being movable between a first limiting position whereby said valve member is disposed in a substantially occluding relationship relative to said housing inlet and a second limiting position where said valve member is disposed in a substantially non-occluding relationship relative to said housing inlet; there being a drive means including an electric motor for extending a linear actuator along the common axis, towards the housing inlet and for retracting the linear actuator along the common axis away from the housing inlet, said linear actuator having an extension member connected thereto having an end adapted selectively to abut the contact end of said valve member and there being a pressure sensor for sensing the pressure of the gas discharged from the compressor and generating a signal representative of the sensed pressure of the discharged gas; the apparatus further comprising an electronic controller including preprogrammed logic for setting an acceptable pressure range that represents a range within which the compressor can operate continuously under load, the electronic controller being in signal receiving relation with the pressure sensor for receiving the sensed pressure signal therefrom, the controller logic including a routine for comparing the sensed pressure signal of the discharged gas to the acceptable pressure range, the electronic controller being in signal sending relation with the drive means for sending signals to the motor for extending and retracting the linear actuator; whereby, during compressor loaded operation the electronic controller generates a signal for retracting the linear actuator until the sensed discharge pressure is within the acceptable pressure range, whereby the low pressure gas entering the inlet urges the valve member away from the inlet until the contact end of the valve member abuts contact end of the actuator extension, and upon stopping said compressor, the backflow from the compressor entering the housing discharge port flows against the valve member for urging the valve member into the first limiting position so as to prevent compressed gas from escaping through the housing inlet, whereby the valve member is urged into the first limiting position solely by the backflow flowing against the valve member. According to a second aspect of the present invention, there is provided a method for controlling the flow of inlet gas and preventing backflow in a compressor (12) where said compressor is flow connected to an apparatus comprising a housing (14) having a chamber (34), a housing inlet (16) for receiving low pressure gas, a housing discharge port (20) for flowing said low pressure gas to the compressor and for receiving backflow from the compressor; a valve member (70) movable within said chamber along a path having a first limit where said valve member is in a substantially occluding position relative to the inlet (16) and a second limit where said valve member is in a substantially non-occluding relationship relative to said inlet; and means (80) for moving the valve member toward said substantially occluding position, said drive means including a linear actuator (82), including a motor (81), movable towards and away from said valve member, said method comprising the following steps: a) setting - using an electronic controller (100), an acceptable pressure range within which the compressor can operate continuously under load; b) starting the compressor and drawing low pressure gas into the compressor through said housing; c) measuring the discharge pressure of the compressed gas; d) determining if the discharge pressure falls within an acceptable pressure range; e) moving said valve member towards the housing inlet if the discharge pressure is outside the acceptable pressure range and is indicative of a decreased demand for low pressure gas, by actuating said means to move the valve member; f) moving said valve member away from the housing inlet if the discharge pressure is outside the acceptable pressure range and is indicative of an increased demand for low pressure gas, by moving said actuator away from said valve member and flowing low pressure gas through said inlet and against said valve member forcing the valve member away from said inlet; and g) if backflow is present in said chamber, using said backflow to move the valve member to the substantially occluding position. For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- Figure 1 is a schematic diagram including apparatus for controlling the flow of low pressure gas to a compressor and preventing backflow from the compressor, Figure 2 is a longitudinal sectional view of an inlet valve showing a valve member in a substantially occluding position; Figure 3 is a longitudinal sectional view of the inlet valve showing the valve member in a substantially non-occluding position; Figure 4 is an enlarged view of the valve member shown in Figure 2 with the valve member at a position between the occluding and non-occluding positions; Figure 5 is an enlarged isometric view of the linear drive shown in Figure 2; and Figure 6 is a longitudinal sectional view of the inlet valve with the valve member located in the substantially occluding position by backflow. Referring to the drawings, wherein similar reference characters designate corresponding parts throughout the several views, Figure 2 illustrates a compressor inlet valve 10 for a gas compressor 12. The inlet valve serves both to regulate the throughput or capacity of the compressor and also to prevent backflow in the compressor. Hereinafter for clarity, "backflow" shall mean any gas or gas/oil combination. The valve 10 replaces discrete check valves in the service and oil lines of compressed air systems known in the art. Conventional discrete check valves prevent backflow in known compressed air systems. The inlet valve is in fluid communication with a compressor 12. In the preferred embodiment, the inlet valve is used in combination with an oil-flooded, rotary screw compressor. However the inlet valve may also be used in combination with a non-lubricated rotary screw compressor. The compressor includes a compressor inlet 21 and discharge port 25. As shown in Figures 2 and 3, the inlet valve 10 includes an inlet housing 14 which has a housing inlet 16 which communicates with inlet ducting 18, a housing discharge port 20 which is flow connected to a compressor inlet 21 by conventional connection means 22, and an anti-rumble gas inlet 23. The anti-rumble inlet must extend through the housing at a location away from the housing inlet 16 as shown in Figure 2. The inlet ducting 18 is connected to the housing inlet 16 by a conventional clamping apparatus 24. The housing 14 also includes housing opening 26, which extends through the housing opposite the housing inlet. A first interior surface 28 defines the housing inlet through which low pressure gas such as air flows into the housing. A second interior surface 30 defines the housing discharge port through which the low pressure gas exits the inlet valve housing and flows to the compressor and through which backflow flows from the compressor. A third interior surface 32 defines a substantially cylindrical inlet chamber 34 which fluidly communicates with the housing inlet 16 and discharge port 20. The housing inlet is surrounded by a valve seat 36 which extends away from the inlet 16 towards an inlet chamber 34 as shown in Figure 3. A mounting plate 38 is adapted to be seated in the housing opening 26. As shown in Figure 4, a conventional gasket member is sandwiched between the periphery of the mounting plate and the housing 14, when the plate is secured to the housing by conventional fasteners 42. The mounting plate has a first face 44 and a second face 46. A guide member 48 is made integral with the mounting plate 38 along the second face 46. When the mounting plate is seated in the opening 26, the guide member is located within the inlet chamber 34 with a guide member free end 50 positioned away from the housing opening 26 and second face 46 facing the inlet chamber 34. A bore 52 extends along longitudinal axis 53 through the guide and plate and has discrete lengths with different diameters. The discrete diameters of the bore 52 are shown in Figure 4. The bore 52 forms an opening 54 on the first plate face 44 and also forms an opening 56 at the guide member free end 50. As shown in Figure 4, a seal 60, such as a lip seal, is disposed in the portion of the bore 52 between the shoulder 58 and opening 54, and a bushing 64 is disposed in the bore at the free end 50 of the guide member 48. A valve member 70 is movable, relative to the guide member, within housing chamber 34 and along a predetermined path defined by axis 53. The path has a first limiting position where the valve member is in a substantially occluding position relative to housing inlet 16, see Figure 2, and a second limiting position where the valve member is in a substantially non-occluding position relative to the housing inlet, see Figure 3. The valve member includes a poppet 71 and a valve stem 72 which is threadably connected to the poppet so that the stem and poppet are movable together within the chamber 34 and along the predetermined path. The valve stem is located in the bore 52 and includes a contact end 73 which is positioned within the bore 52 near the shoulder 58. The poppet and valve stem are movable linearly along the predetermined path. Additionally, during operation of the compressor, in order to obtain the desired compressed gas discharge pressure, the valve member may be located at any location along the predetermined path, between the first and second limiting positions. The poppet 71 includes a leading face 74, a trailing face 76 and a valve stop 78 along the periphery of the leading face of the poppet. The stop is adapted to abut the housing seat 36 in the manner shown in Figure 2 when the valve is in the substantially occluding position. A drive 80 is a linear actuator that replaces the pneumatic and hydraulic drives and stepper motors that are well known in the art. The linear actuator includes a direct current (DC) powered electric motor 81 that extends and retracts an actuator 82 along axis 53. Conventional gearing provides the required gear ratios (typically 10:1) between the actuator and the motor. The actuator thrust is provided using a ball screw mechanism that is known in the art. In the preferred embodiment, the linear drive is designed to provide at least 1000 pounds (453.6 kg) of thrust to the actuator 82. The linear drive may be of the type manufactured by Warner Electric Corporation which provides at least 1000 pounds (453.6 kg) of actuator thrust force. Hereinafter, the terms linear actuator or linear drive shall mean an apparatus having a motor that displaces an actuator member linearly when power is supplied to the motor. The linear actuator is in communication with a controller 100 which is described in detail hereinafter. As shown in Figure 5, a bracket 90 supports the linear actuator 80 and encloses a portion of actuator extension 84. The actuator extension is connected to the end of the actuator 82 and is moveable linearly, along the axis 53 with the actuator. The bracket includes an open end 95, a closed end 96, sidewalls 92 having longitudinal slots 93, and flange portions 94 at the open end. The flanges are mounted, in a conventional manner, on the first face 44 of the mounting plate 38. The actuator extension 84 is connected to the actuator 82 by an anti-rotation pin 97, the respective ends of which are located in slots 93 to be movable linearly in the slots during extension and retraction of the actuator and actuator extension. In this way, the pin 97 prevents rotation of the actuator during operation. Lugs 99 are mounted on the closed end 96 and are adapted to receive the ends of a second pin, like pin 97. In this way, rotation and displacement of the rear portion of linear actuator 80 is prevented. The actuator extension contact end 86 is adapted to abut the contact end 73. The actuator extension 84 extends through the bracket open end 95 to a location within the bore 52 with the actuator extension end 86 located immediately proximate or in abutment with the valve stem contact end 73. The valve stem and actuator extension are not connected. Therefore, when it is necessary to close the valve, the actuator and actuator extension are together extended and moved toward the inlet 16 and the actuator extension end 86 abuts the valve stem end 73 and by this abutment, urges the valve member 70 along the predetermined path, toward the inlet 16. However, since the stem and valve are not connected, when the actuator extension and actuator are retracted and moved away from the inlet 16, the actuator extension does not pull the valve member 70 away from the inlet 16. Rather, as the actuator extension is withdrawn, the gas drawn through the housing inlet flows against the poppet contact face 74, as indicated by arrows 66 in Figure 3, and forces the valve member away from the inlet 16 along the predetermined path, keeping the contact end 73 in abutment with the contact end 86. Additionally, when backflow flows through the compressor inlet 21 and housing discharge port 20, the gas flows against the poppet trailing face 76, as indicated by arrows 67 in Figure 6, and rapidly forces the valve member toward the inlet 16, to the substantially occluding position shown in Figure 2, thereby closing the housing inlet and preventing backflow from exiting the housing. As shown in Figure 6, when the valve member is closed by backflow, the contact end 73 is moved out of abutment with the end 86. Pressure sensing means 98 is located in pressure sensing communication with a separator tank 104 and senses the discharge pressure of the compressed gas. Additionally, the sensing means generates a signal in response to the discharge pressure sensed by the pressure sensing means. As shown schematically in Figure 1, the pressure sensing means is in signal transmitting communication with the electronic microprocessor based controller 100 so that the generated signal is communicated to the controller. The sensing means may be a pressure transducer or the like. Also shown in Figure 1, controller 100 is located in signal receiving relation with respect to the pressure sensing means 98, and is located in both signal transmitting and receiving relation with respect to the linear actuator 80. The controller is located in signal transmitting relation to a solenoid valve 102. A desired operational discharge pressure for a specific application, hereinafter referred to as "set point" pressure is programmed in the logic stored in the controller. The set point pressure represents the desired compressor discharge pressure. Also programmed in the controller is a variable deadband pressure range. The deadband range represents the acceptable pressure range which includes the set point pressure. For example, if the set point pressure is 115 psi (792.93 Kn/m 2 ), and the acceptable variation in the set point pressure is ± 5 psi (34.48 Kn/m 2 ), the acceptable pressure range or deadband range would be 110 psi to 120 psi (758.45 - 827.40 Kn/m 2 ). A conventional separator tank 104 is in fluid communication with the compressor discharge port and serves to separate a fluid, such as oil, from the compressed gas. The essentially dry gas flowing from the tank may flow to the customer via a service valve 106 or may be redirected to the anti-rumble inlet 23. The solenoid valve 102 is flow connected to the separator tank 104. When the valve member 70 is in a substantially occluding position, the solenoid is actuated by the controller and opens the anti-rumble valve permitting gas exiting the tank to be reflowed to the compressor inlet and in this way, prevent vibration of the rotors referred to in the art as rumble condition. A minimum pressure valve 105 is in flow communication with the interior of the separator tank. The minimum pressure valve maintains a minimum pressure in the tank in order to maintain oil flowing through the compressor. In operation, a set point discharge pressure is entered into the controller where it is stored. The acceptable variation in the set point pressure is also entered and stored in the controller. The sensor 98 is located in pressure sensing communication with the interior of the tank 104. The valve member 70 is in a substantially occluding position when the compressor 12 is started. The actuator 82 is extended and the contact end 86 of the actuator extension 84 is in abutment with the contact end 73 and thereby maintains the valve in the substantially occluding position shown in Figure 2 during startup. The solenoid valve 102 is actuated by the controller 100 thereby permitting anti-rumble gas to flow through the anti-rumble inlet 23 to the compressor 12. The solenoid valve 102 remains open until the valve member 70 is opened. After the compressor has been started, and is warmed up, power is supplied to the linear actuator motor 81 which retracts the actuator 82 along the axis 53 and away from the inlet 16. As the actuator extension is moved away from the inlet, gas drawn through the inlet 16 acts against the face 74, and the greater pressure on face the 74, as compared to the face 76, forces the valve member 70 away from the housing inlet 16. As the valve member 70 is moved away from the inlet 16, the solenoid valve 102 is closed by the controller. The resultant pressure, representing the difference between the flow pressures acting on faces 74 and 76, moves the valve away from the inlet 16, until the contact end 73 abuts the end 86 of the actuator extension 84. The inlet vacuum in the cavity 34 decreases as the inlet valve is opened as gas is drawn into the housing by the compressor. The discharge pressure is continuously monitored by the sensing means 98 which generates a signal in response to the sensed pressure and communicates the signal to the controller 100. The controller executes a preprogrammed logic routine and compares the sensed pressure to the preprogrammed acceptable pressure range. The actuator is retracted until the discharge pressure is in the acceptable range. When the discharge pressure is in the acceptable range, the motor 81 is turned off by the controller and further displacement of the valve member away from the inlet 16 is prevented by the stationary actuator extension 84. The linear actuator rapidly and accurately permits the valve member to move along the predetermined path to the position required to produce an acceptable discharge pressure. The proper position is determined by the measured discharge pressure. The proper position typically is located along the path between the occluding and non-occluding positions. The valve member is moved away from the inlet 16 when the pressure is below the acceptable range and it is necessary to increase the load to the compressor. If the actuator reaches the end of travel so that the valve member is in the substantially non-occluding position of Figure 3, the controller receives a locked rotor current from the linear drive, indicating the actuator has reached the end of travel. Then power to the DC motor is interrupted causing the motor to shut off. The locked rotor current includes a direction signal which indicates the direction of travel of the actuator to the controller. In this way the controller microprocessor can determine electronically if the valve member has reached the end of travel in the non-occluding or occluding position. If, during compressor operation, the discharge pressure measured by the sensing means 98, is above the preprogrammed acceptable pressure range, and it is necessary to move the valve member toward the inlet 16, the controller supplies power to the motor 81 which extends the actuator 82 and simultaneously moves the actuator extension along axis 53, toward the inlet 16. The contact end 86 of the actuator extension abuts the contact end 73 and thereby urges the valve member along the predetermined path of movement toward the inlet. The pressure sensor continuously monitors discharge pressure in the manner previously described and the actuator is extended until the discharge pressure falls into the acceptable pressure range, at which time the controller interrupts power to the motor. The actuator provides a thrust that is of sufficient magnitude to overcome the pressure of the gas or air drawn into the housing inlet. If, during operation, the valve member reaches the substantially occluding position shown in Figure 2, a locked rotor current like the locked rotor current previously described is transmitted from the linear actuator and is received by the controller. When the locked rotor current is received by the controller, the supply of power to the motor is interrupted and the solenoid valve 102 is opened permitting anti-rumble air to the compressor 12. Movement of the valve member is determined solely by the discharge pressure of the compressor. The valve member 70 is opened or closed based on the measured compressed gas discharge pressure. Based on the measured discharge pressure, the valve member may be moved along the predetermined path and located at the occluding position, the non-occluding position or at a position along the path therebetween. When the compressor is stopped, backflow will flow from the compressor out compressor inlet 21. If the valve member 70 is open, the backflow flows against the trailing face 76 of the valve member in the manner indicated by the arrows 67 in Figure 6. The backflow rapidly moves the valve into the substantially occluding position shown in Figure 6. The higher pressure on the face 76, as opposed to face 74, closes the valve member. In this way, the flow of oil and gas from the compressor and out the housing inlet is prevented. When the valve member is forced shut by the backflow, ends 73 and 86 are moved out of abutment. The two ends remain out of abutment until the compressor is turned on, gas is again drawn through the housing inlet and the valve member is forced away from the inlet in the manner previously described.

Claims: An apparatus (10) for controlling the flow of low pressure gas to a compressor (12) and preventing backflow of compressed gas from the compressor, the apparatus comprising a housing (14) for fluid communication with the compressor (12), said housing having a chamber (34), a housing inlet (16) for receiving low pressure gas, and a housing discharge port (20) for allowing said low pressure gas to flow to said compressor and through which backflow flows, in use, from said compressor, and a valve member (70) having a valve stem (72) connected to said valve member and having a contact end (73), said valve member being movable within said chamber (34) towards and away from said inlet (16) along a common axis (53), said valve member being movable between a first limiting position whereby said valve member is disposed in a substantially occluding relationship relative to said housing inlet and a second limiting position where said valve member is disposed in a substantially non-occluding relationship relative to said housing inlet; there being a drive means (80) including a motor (81) for extending a linear actuator (82) along the common axis, towards the housing inlet (16) and for retracting the linear actuator (82) along the common axis away from the housing inlet (16), said linear actuator having an extension member (84) connected thereto having an end (86) adapted selectively to abut the contact end (73) of said valve member (70) and there being a pressure sensor (98) for sensing the pressure of the gas discharged from the compressor and generating a signal representative of the sensed pressure of the discharged gas; characterised by the motor (81) being an electric motor and by an electronic controller (100) including preprogrammed logic setting an acceptable pressure range within which the compressor can operate continuously under load, the electronic controller being in signal receiving relation with the pressure sensor (98) for receiving the sensed pressure signal therefrom, the controller logic including a routine for comparing the sensed pressure signal of the discharged gas to the acceptable pressure range, the electronic controller being in signal sending relation with the drive means (80) for sending signals to the motor (81) for extending and retracting the linear actuator (82); whereby, during loaded compressor operation, the electronic controller generates a signal for retracting the linear actuator (82) until the sensed discharge pressure is within the acceptable pressure range, whereby the low pressure gas entering the inlet (16) urges the valve member away from the inlet until the contact end (73) of the valve member (70) abuts contact end (86) of the actuator extension (84), and upon stopping said compressor, the backflow from the compressor entering the housing discharge port (20) flows against the valve member (70) for urging the valve member into the first limiting position so as to prevent compressed gas from escaping through the housing inlet (16), whereby the valve member (70) is urged into the first limiting position solely by the backflow flowing against the valve member. An apparatus according to claim 1, wherein said pressure sensor (98) is a pressure transducer and is located in pressure sensing communication with a separator tank (104). An apparatus according to claim 1, 2 or 3, wherein said housing (14) includes a housing opening opposite said housing inlet (16), the apparatus further comprising a mounting plate (38) adapted to be seated in said housing opening and a guide member (50) integral with said plate, said guide member and plate including a bore (64) that extends through said plate and guide, said bore being adapted slidably to receive said valve stem (72) and said actuator extension (84). An apparatus according to claim 1, 2 or 3, and further including anti-rotation means (97) for preventing, rotation of said actuator during movement of said actuator. An apparatus according to claim 4, further comprising a bracket (90) supporting said linear drive, said bracket including an open end (95), a closed end (96) and a pair of side walls (92) between said ends, each side wall having a slot (93) formed therein, said anti-rotation means comprising a pin (97) having ends respectively slidably located in said slots. An apparatus according to claim 5, wherein said anti-rotation means includes lugs (99) mounted on said bracket closed end (96), said lugs being adapted to receive a second anti-rotation pin to prevent rotation and displacement of said linear drive. An apparatus according to any one of the preceding claims, wherein said valve member (71) includes a leading face (74) with a valve stop (78) located on the leading face. An apparatus according to any one of the preceding claims, wherein the housing includes an anti-rumble gas inlet (23) for providing anti-rumble gas to the compressor. A gas compressor incorporating an apparatus according to any one of the preceding claims. A compressor according to claim 9 and being an oil-flooded rotary screw compressor. A compressor according to claim 9 and being a non-lubricated rotary screw compressor. A method for controlling the flow of inlet gas and preventing backflow in a compressor (12) where said compressor is flow connected to an apparatus comprising a housing (14) having a chamber (34), a housing inlet (16) for receiving low pressure gas, a housing discharge port (20) for flowing said low pressure gas to the compressor and for receiving backflow from the compressor; a valve member (70) movable within said chamber along a path having a first limit where said valve member is in a substantially occluding position relative to the inlet (16) and a second limit where said valve member is in a substantially non-occluding relationship relative to said inlet; and means (80) for moving the valve member toward said substantially occluding position, said drive means including a linear actuator (82), including a motor (81), movable towards and away from said valve member, said method comprising the following steps: a) setting - using an electronic controller (100), an acceptable pressure range within which the compressor can operate continuously under load; b) starting the compressor and drawing low pressure gas into the compressor through said housing; c) measuring the discharge pressure of the compressed gas; d) determining if the discharge pressure falls within an acceptable pressure range; e) moving said valve member (70) towards the housing inlet (16) if the discharge pressure is outside the acceptable pressure range and is indicative of a decreased demand for low pressure gas, by actuating said means to move the valve member; f) moving said valve member away from the housing inlet if the discharge pressure is outside the acceptable pressure range and is indicative of an increased demand for low pressure gas, by moving said actuator away from said valve member and flowing low pressure gas through said inlet and against said valve member forcing the valve member away from said inlet; and g) if backflow is present in said chamber, using said backflow to move the valve member to the substantially occluding position. A method according to claim 12 and including the step of putting a sensor (98) in pressure communication with a separator tank (104) before performing step (c). A method according to claim 12 or 13, wherein if the sensed discharge pressure is above the acceptable pressure range the electronic controller (100) generates a signal for extending the linear actuator (84) toward the first limiting position whereby the contact end (86) of the actuator extension member (84) abuts against the contact end (73) of the valve stem (72) for urging the valve member (70) toward the inlet, the actuator (82) being extended until the sensed discharge pressure falls within the acceptable pressure range. A method, according to claim 12, 13 or 14, wherein during startup of the compressor the electronic controller sends a signal to the drive means for extending the linear actuator whereby the contact end (86) of actuator extension (84) abuts the contact end (73) of the valve member (70) for maintaining the valve member (70) in the first limiting position, the position of the valve member being determined solely by the sensed discharge pressure whereby the valve member is positionable at the first limiting position, the second limiting position or at a plurality of locations between the first limiting position and the second limiting position. A method according to claim 12, 13, 14 or 15 and including the steps of: after step d) supplying power to said motor when the discharge pressure is not in the acceptable range and continuing to supply power to said motor until the discharge pressure is in the acceptable range. A method according to any one of claims 12 to 16, wherein said housing (14) includes a means (23) for providing anti-rumble gas to the compressor, said method including the steps of actuating the anti-rumble means and flowing anti-rumble gas to the compressor (12) when the valve member (70) is in the substantially occluding position. A method according to any one of claims 12 to 17 and including the step of transmitting a locked rotor current by said drive means (80) when the valve member (70) is in either of the limiting positions. A method according to claim 18 and including the step of actuating a solenoid valve (102) and flowing anti-rumble gas to the housing when the valve member (70) is in the substantially occluding position.

Inventors: GUNN JOHN T, HARDEN WILLIAM T, GUNN, JOHN T., HARDEN, WILLIAM T.
Applicants: INGERSOLL RAND CO, INGERSOLL-RAND COMPANY
Application year: 1996
Main classification: F04C29
IPC codes: F04B39, F16K15, F04B49, F16K31, F15B13, F04C28, F04C29, F04C18