Abstract:
An inlet valve for use in a gas compressor, the inlet valve including a piston movable within a housing chamber toward and away from a housing inlet and a valve disc movable with the piston, the valve disc including an aperture for selectively providing air flow from the housing inlet into the chamber, and a flexible member engageable with the valve disc to close the aperture. The inlet valve also includes a valve seat disposed near the housing inlet, and the piston is movable between a first position where the valve disc contacts the valve seat, and a second position where the valve disc is spaced from the valve seat. A spring biases the valve disc toward the valve seat.

Description:
FIELD OF INVENTION 
     The present invention relates to gas compressors, and more particularly to inlet control valves for gas compressors. 
     BACKGROUND OF INVENTION 
     Inlet control valves are commonly used on gas compressors to regulate compressor capacity. These valves control the capacity by limiting the intake air that enters the compressor. An unloader valve is a valve that loads and unloads the compressor, and is often used as an inlet control valve. An compressor unloader valve is “loaded” when the valve is open and gas can pass through it, and “unloaded” when the valve is closed and blocks the flow of gas into the compressor. 
     Pneumatic, hydraulic, and electronic methods have been used to open and close unloader valves. Several unloader valves are two-position valves and only have an open position and a closed position. These valves are not able to modulate to positions between these two extremes, and this limited number of settings can reduce the effectiveness of a compressor. 
     Additionally, pneumatic unloader valves typically use some type of a piston and cylinder configuration to open and close the valve, and can suffer from a “stick/slip” problem between sliding surfaces sealed with O-rings. The initial force necessary to overcome the static friction between the sliding surfaces of the piston and cylinder is often greater than that needed to overcome the sliding force. Therefore, a larger force must be applied to initially move the piston, but once it is moving, the resistive force is not as large and the piston moves too far. 
     The stick/slip problem is not of great concern for two-position valves because they are only moving between two extreme positions from the open position to the closed position, and do not stop in between. However, this can be a serious problem with modulating valves because it creates erratic piston movement that is segmented, or choppy, not the smooth controlled movement needed for a modulating valve. The piston will generally move past the desired position, and must be brought back to the proper location. 
     A problem experienced in oil-flooded compressors is backflow of a gas and oil combination through the air inlet. Backflow can take place when a compressor stops while the system is still pressurized. In this situation, the compressor system has a higher pressure than the atmospheric inlet, so the gas and oil mixture can be forced toward the lower pressure and out the inlet. Prior art arrangements seek to solve this problem by utilizing spring loaded check valves that only allow one-directional flow. These additional check valves are effective, but they increase the cost and complexity of a compressor. 
     Noise reduction also a concern with gas compressors. Some prior art unloader valves allow the internal noise of the compressor to escape through the inlet valve while it is open. Inlet valves that provide a straight path from the air intake to the compressor are relatively loud because there are fewer mechanisms to block noise as it exits through the valve. 
     Another noise problem for compressors is known as “rotor rumble” in the industry. This condition occurs when the control valve is unloaded and pressure builds up in the compressor system. Compressors generally relieve this pressure by discharging “blowdown” air. In an oil-filled compressor, the blowdown air is an air and oil mixture and can cause contamination if it is discharged into the atmosphere, or into the compressor package. Some compressors solve this problem by piping the blowdown air to discharge into the intake valve downstream from the air intake filter. Since this cavity is at atmospheric pressure, and the blowdown air is at a higher pressure, the blowdown air expands suddenly and produces an undesirable noise. 
     SUMMARY OF INVENTION 
     The invention provides an air compressor including a pneumatic modulating inlet unloader valve that does not experience stick/slip, prevents backflow, prevents rotor rumble, and reduces the noise of blowdown air. The inlet unloader valve includes a housing with a main chamber, a housing inlet, and a housing outlet. Air enters the housing through the housing inlet and exits the housing through the housing outlet. A piston chamber is located within the main chamber, and a piston is at least partially disposed in the piston chamber. The piston is movable within the piston chamber toward and away from the housing inlet. 
     A valve disc is mounted to the piston, and is movable with the piston. A valve seat is disposed near the housing inlet, and the valve disc contacts the valve seat to create a seal and close the inlet valve. The valve disc is mounted around the piston, and a spring biases the piston towards the closed position and holds the valve disc against the valve seat. The inlet valve is closed, or “unloaded” when the valve disc contacts the valve seat, and open, or “loaded”, when the valve disc is separated from the valve seat. Preferably, the inlet valve is normally in the closed position. 
     The valve disc has an aperture and a flexible member that comprise a plate valve. The plate valve selectively provides air flow from the housing inlet into the main chamber, and the flexible member can contact the valve disc to close the apertures. When the pressure within the compressor reverses, the plate valve preferably seals the apertures to prevent backflow. 
     A piston retainer preferably surrounds a portion of the piston, and is also disposed within the piston chamber. A control cavity is disposed within the piston chamber, and is at least partially defined by the piston, the piston retainer, and the piston chamber. The control cavity preferably creates a space between the piston and the piston retainer in which a pneumatic signal can be injected to separate the piston from the piston retainer. A control port is interconnected to the housing, and a control inlet runs through the control port and is in fluid flow communication with the control cavity. The pneumatic signal passes through the control inlet and into the control cavity. 
     The pneumatic signal is used to control the position of the piston. The pneumatic signal works against the spring and moves the piston away from the housing inlet. When the piston moves away from the housing inlet, the valve disc moves with it and separates from the valve seat. The inlet valve can preferably be opened, closed, and placed in any position using a pneumatic signal. 
     Air compressors must often discharge air to relieve internal pressure. The discharged air is commonly called blowdown air, and creates an undesirable noise if it is vented to an area at a lower pressure. The inlet valve preferably has a blowdown port with a silencer interconnected to the housing inlet where the blowdown air can be discharged. Preferably, the blowdown air is drawn back into the compressor through the plate valve, so any oil or contamination in the blowdown air is contained within the compressor system. The silencer has multiple apertures to breakdown the air stream into multiple smaller streams and dissipate the noise often caused by venting the blowdown air. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an inlet unloader valve embodying the present invention. 
     FIG. 2 is a front elevation view of the valve shown if FIG.  1 . 
     FIG. 3 is a cross-sectional view, taken along line  3 — 3  of FIG. 2, showing the valve in the closed, or unloaded, position. 
     FIG. 4 is a cross-sectional view, taken along line  4 — 4  of FIG.  2 . 
     FIG. 5 is an enlarged view of a portion of FIG.  4 . 
     FIG. 6 is a view similar to FIG. 3, but showing the valve in the open, or loaded, position. 
    
    
     Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
     DETAILED DESCRIPTION 
     FIG. 1 illustrates the exterior of an inlet unloader valve  10  for a gas compressor. The inlet valve  10  has a housing  14  with a main chamber  18 , a housing inlet  30 , a housing outlet  34 , a control port  120 , and a blowdown port  124 . The gas compressor in the preferred embodiment is an oil-flooded, rotary screw air compressor, but the inlet valve  10  could also be used on other compressors. The inlet valve  10  is preferably interconnected to the compressor, an air intake conduit  32 , a control system conduit  122 , and a blowdown conduit  126 . The inlet valve  10  is intended to regulate the capacity of the compressor. 
     In the preferred embodiment, various elements of the inlet valve  10  are predominantly circularly or cylindrically shaped. Preferably, the main chamber  18 , housing inlet  30 , housing outlet  34 , control port  120 , and blowdown port  130  are all substantially cylindrical. In FIG. 3, the piston chamber  22 , piston  40 , piston retainer  60 , and valve disc  70  preferably have a predominantly cylindrical or circular shape. A cylindrical configuration is not necessary for the invention to function, but cylindrical bodies often have desirable strength characteristics for use in pressure vessels. In the preferred embodiment, the housing inlet  30  and the housing outlet  34  are substantially perpendicular. This angled arrangement reduces the amount of noise from the compressor that travels back through the inlet valve  10  into the atmosphere. 
     The housing inlet  30  preferably receives air through the housing inlet conduit  32  (FIG.  3 ). FIG. 2 represents a view looking into the inlet valve  10  through the housing inlet  30 , and shows the valve disc  70  disposed near the housing inlet  30 . When the inlet valve  10  is closed, the valve disc  70  abuts the valve seat  74  near the end of the housing inlet  30 . Also shown in FIG. 2 are the housing outlet  34 , the control port  120 , and the blowdown port  130 . The air that enters the housing  14  through the housing inlet  30  preferably exits through the housing outlet  34  as it passes into the compressor. 
     In the preferred embodiment, the control port  120  interconnects with the main chamber  18 , and the blowdown port  130  is interconnected with the housing inlet  30 . The control port  120  and the blowdown port  130  are preferably disposed on opposite sides of the housing  18 . However, it is not necessary for the control port  120  and blowdown port  130  to be located at these exact points. The control port  120  could be located radially around the circumference of the main chamber  18 , as long as it does not interfere with the housing outlet  34 . Likewise, the blowdown port  130  could be relocated radially around the circumference of the housing inlet  30 . 
     FIG. 3 is a cross-sectional view showing the internal components of the inlet valve in the closed position. In the preferred embodiment, the inlet valve  10  is pneumatically modulated and is normally in the closed position. Essentially, the inlet valve  10  uses pneumatic pressure to modulate a piston  40  interconnected to a valve disc  70 . A spring  56  preferably acts against a piston  40  that presses a valve disc  70  against a valve seat  74  to maintain the inlet valve  10  in the closed position. To open the inlet valve  10 , a pneumatic force preferably moves the piston  40  against the spring  56  and separates the valve disc  70  from the valve seat  74 . The operation of the inlet valve  10  will be explained in greater detail below. 
     The piston chamber  22  is disposed radially inwardly from the main chamber  18 , and is preferably cylindrical with one open end  24  and a back surface  26  at the other end. The spring  56  and piston retainer  60  are preferably disposed within the piston chamber  22 . The piston  40  is at least partially disposed within the piston chamber  22 , and preferably extends through the open end  24  toward the housing inlet  30 . The piston  40  preferably has a hollow core  62 , and the spring  56  is partially disposed within the core  62 . The spring  56  is preferably retained by the piston bore  64  at one end, and the housing bore  28  at the other end. 
     The piston  40  is preferably a segmented cylinder with a chamber surface  52 , a retainer surface  48 , a slanted face  54 , and a stem  44 . The chamber surface  52  is preferably near the end of the piston  40  closest to the back surface  26 , the stem  44  is preferably near the end of the piston  40  closest to the housing inlet  30 , and the retainer surface  48  is preferably disposed between the chamber surface  52  and the stem  44 . The diameter of the piston  40  is the largest at the chamber surface  52 . The diameter preferably decreases from the chamber surface  52  to the retainer surface  48 , and decreases once again to the stem  44 . The slanted face  54  leads from the retainer surface  48  to the stem  44 , and is not perpendicular to either of those surfaces. 
     The spring cavity  58  is disposed within the piston chamber  22  between the piston  40  and the back surface  26 , and is in fluid flow communication with the core  62 . The piston  40  preferably has a stem vent  42  that extends through the stem  44  and allows the spring cavity  58  to be in fluid flow communication with the housing inlet  30 . There is preferably a seal between the chamber surface  52  and the piston chamber  22 , so the stem vent  42  prevents pressure from building up in the spring cavity  58  and core  62 . 
     The chamber surface  52  preferably contacts the interior surface of the piston chamber  22 . In the preferred embodiment, there is a chamber wear ring  108  and a chamber O-ring  112  along the chamber surface  52 . The chamber O-ring  112  preferably creates a seal between the chamber surface  52  and the piston chamber  22 . The chamber wear ring  108  preferably facilitates movement and reduces friction between the chamber surface  52  and the piston chamber  22 . 
     The piston retainer  60  is preferably disposed between the piston  40  and the piston chamber  22 , and contacts the piston chamber  22  and retainer surface  48 . In the preferred embodiment, there is a retainer wear ring  100  and a retainer O-ring  104  along the retainer surface  48 . The retainer O-ring  104  preferably creates a seal between the retainer surface  48  and the piston retainer  60 . The retainer wear ring  100  preferably facilitates movement and reduces friction between the retainer surface  48  and the piston retainer  60 . 
     In the preferred embodiment, a retainer ring  61  provides support for the piston retainer  60 , counteracts the force from the spring  56 , and retains the piston retainer  60  and the piston  40  in the proper position while the inlet valve  10  is closed. The retainer ring  61  is preferably an internal circlip. When the inlet valve  10  is in the closed position, the retainer shoulder  50  also preferably contacts the piston retainer  60 . The size of the piston retainer  60  is preferably calibrated so that when the retainer shoulder  50  contacts the piston retainer  60 , the valve disc  70  also contacts the valve seat  74 . 
     The valve disc  70  is preferably disposed around the stem  44 . The piston  40  preferably has a valve shoulder  66  that abuts the valve disc  70  while the inlet valve  10  is closed. A stem O-ring  46  preferably creates a seal between the valve disc  70  and the stem  44 , and a stem ring  45  preferably retains the valve disc  70  around the stem  44 . In the preferred embodiment, the stem ring  45  is an external circlip. The fit of the valve disc  70  on the stem  44  preferably allows for some angular movement, so the valve disc  70  can self-adjust onto the valve seat  74  and provide a more air-tight seal while the inlet valve  10  is closed. 
     The valve disc  70  preferably has a plate valve  78  comprised of valve apertures  82  (FIG. 4) and a flexible member  86  to prevent backflow. The flexible member  86  can preferably contact the valve disc  70  to close the plate valve  78 , and flex away from the valve disc  70  to open the plate valve  70 . The slanted face  54  preferably allows clearance for the flexible member  86  to bend, while the valve shoulder  66  contacts the valve disc  70  to hold it in the closed position. 
     FIG. 4 is another cross-sectional view of the inlet valve  10 , and shows the valve apertures  82  of the plate valve  78 . There are two valve apertures  82  in the preferred embodiment, but only one aperture or additional apertures could also be used. The plate valve  78  preferably allows small amounts of make-up air to enter the main chamber while the inlet valve  10  is closed. Since the inlet valve  10  of the preferred embodiment is normally closed, the plate valve  78  and make-up air are of great importance. This makeup air is often necessary to keep a small amount of flow moving through the compressor to maintain the lubrication pressure in the system while the inlet valve  10  is closed. The plate valve  78  is a one-way valve that preferably allows make-up air to enter the compressor, but prevents backflow from exiting the compressor. 
     When a compressor stops, there is often a pressure reverse back through the inlet. This condition is commonly called backflow, and is undesirable in oil-flooded compressors in which oil is mixed with the air. The backflow of oil could contaminate the air filter or the external environment. The flexible member  86  allows make-up air to flow through the valve disc  70  and into the main chamber  18 , but seals the apertures  82  to prevent backflow. 
     Normally, the pressure in the main chamber  18  is lower than the pressure in the housing inlet  30 , so the make-up air flows from the higher pressure housing inlet  30  to the lower pressure main chamber  19 . The pressure differential and flow also partially separates the flexible member  86  from the valve disc  70 . When the pressure reverses and the main chamber  18  has a higher pressure than the housing inlet  30 , the flexible member  86  contacts the valve disc  70  and preferably seals the valve apertures  82  preventing backflow oil from exiting the compressor. The plate valve  78  also preferably prevents excessive reverse rotation of the compressor when it is shut down. 
     FIG. 4 also illustrates the blowdown port  130  interconnected to the housing inlet  30 . Compressors must often relieve pressure within the system when they unload, and this is commonly done by discharging blowdown air. The blowdown air usually contains oil, and is often discharged back into the compressor package to reduce contamination to the outside environment. One solution is to pipe the discharged blowdown air into the intake of the inlet valve. In the preferred embodiment, the blowdown port  130  is interconnected to the housing inlet  30 , just upstream from the valve disc  70 . At this location, the oil from the blowdown air is preferably drawn back into the compressor through the plate valve  78  because of the flow of make-up air through the plate valve  78  under normal conditions. This allows the blowdown air to relieve pressure from within the system while containing the contaminated oil and air mixture. 
     One problem with discharging the blowdown air into the air intake is excessive noise. The air in the housing inlet  30  is generally at atmospheric pressure, and the blowdown air comes from within the system and is at a relatively higher pressure. When the higher pressure blowdown air enters the lower pressure air intake in most compressors, it expands suddenly and produces an undesirable noise. In the preferred embodiment, the inlet valve  10  has a built-in silencer  134  in the blowdown port  130  that reduces this noise. The blowdown air in most compressors enters the air intake in a single stream. In the preferred embodiment, the silencer  134  breaks the air stream into several smaller streams to reduce the noise created by the blowdown air. The silencer  134  preferably has multiple silencer apertures  138  to divide the air stream. FIG. 3 illustrates seven silencer apertures  138 , however the silencer  134  could include any number of apertures  138  that sufficiently reduce the noise created by the blowdown air. 
     FIG. 4 illustrates the control port  120  interconnected to the housing  14 . The control port  120  preferably has a control inlet  124  that extends through the main housing  18  and piston chamber  22  and is in fluid flow communication with the control cavity  116 . The control cavity  116  is preferably disposed within the piston chamber  22 , and is at least partially defined by the piston chamber  22 , the piston retainer  60 , and the piston  40 . Preferably, a pneumatic signal enters the control cavity  116  and controls whether the inlet valve  10  is open or closed. A sensor preferably reads the pressure at a certain location, and based on that pressure, a controller determines the desired position for the inlet valve  10 . The controller preferably increases a pneumatic signal to the control cavity  116  to open the inlet valve  10 , or reduces the signal to close the inlet valve  10 . 
     In the preferred embodiment, a spring  56  preferably acts against a piston  40  that is connected to a valve disc  70  to maintain the inlet valve  10  in the closed position. FIG. 4 illustrates the inlet valve  10  in the closed, or “unloaded” position. The valve disc  70  abuts the valve seat  74  to form a seal and preferably prevent air from entering the main chamber  18 . To open the valve  10 , a pneumatic signal enters the control cavity  116  and forces the piston  40  against the spring  56  and away from the housing inlet  30 . The movement of the piston  40  separates the valve disc  70  from the valve seat  74 , and allows air to enter the main chamber  18  from the housing inlet  30 . The compressor is “loaded” when the valve disc  70  is separated from the valve seat  74 . 
     FIG. 5 is an enlarged view of the control cavity  116  and the control inlet  124 . The piston  40  preferably contacts the piston retainer  60  when the inlet valve  10  is closed. A pneumatic signal preferably flows through the control inlet  124  and into the control cavity  116  to separate the retainer shoulder  50  from the piston retainer  60 . FIG. 5 also shows the chamber O-ring  112  and chamber wear ring  108  along the chamber surface  52 , and preferably contacting the piston chamber  22 . 
     Preferably, the piston chamber  22  in FIG. 4 is fixed and the piston retainer  60  is restricted by the retainer ring  61 , but the piston  40  is capable of movement. Therefore, the position of the piston  40  can preferably be controlled by altering the pressure in the control cavity  116 . As mentioned above, the spring  56  preferably biases the piston  40  towards the closed position depicted in FIGS. 3 and 4. Increasing the pressure in the control cavity  116  can preferably move the piston  40  generally towards the back surface  26  and open the inlet valve  10 , as shown in FIG.  6 . 
     FIG. 6 illustrates a cross-sectional view showing the internal components of the inlet valve  10  in an open, or “loaded” position. The inlet valve  10  is completely open with the piston  40  contacting the back surface  26 . While FIGS. 3 and 6 illustrate the inlet valve  10  in the extreme positions, it is capable of modulating the piston  40  to any position between the closed position of FIG.  3  and the closed position depicted in FIG. 6. A modulating inlet valve  10  allows the compressor to operate more efficiently. When the inlet valve  10  is opened, the volume of the control cavity  116  increases, and the volume of the spring cavity  58  decreases. The spring cavity  58  in FIG. 3 is larger than the spring cavity  58  in FIG. 6, and the control cavity  116  in FIG. 6 is larger than the control cavity in FIG.  3 . 
     As illustrated in FIG. 4, the stem vent  42  preferably allows the core  62  and spring cavity  58  to be in fluid flow communication with the housing inlet  30 . With this arrangement, the piston  40  and pneumatic signal in the control cavity  116  do not have to work against air pressure as well as the spring  56 . The air in the spring cavity  56  that is displaced when the piston  40  moves can exit through the stem vent  42 . The spring  56  is preferably calibrated to provide a predetermined amount of resistance which the pneumatic signal can counteract and position the piston  40  in the desired location. 
     A common problem for valves utilizing sliding surfaces sealed with O-rings is a “stick/slip” phenomena. In the preferred embodiment, the inlet valve  10  must have a sealed cavity to use a pneumatic control. The piston  40  preferably has a chamber O-ring  112  to create a seal between the chamber surface  52  and the piston chamber  22 , and a retainer O-ring to create a seal between the retainer surface  48  and the piston retainer  60 . There is also an auxiliary O-ring  114  between the piston retainer  60  and the piston chamber  22 . These O-rings  104 ,  112 ,  114  preferably seal the control cavity  116 . Preferably, the chamber surface  52  slides relative to the piston chamber  22 , and the retainer surface  48  slides relative to the piston retainer  60 . The “stick/slip” phenomena would normally be a problem for most valves, but the inlet valve  10  preferably has wear rings that substantially eliminate the problem. 
     The “stick/slip” problem can occur when an O-ring seals sliding surfaces and the initial force needed to overcome static friction is greater than the sliding friction force. The O-ring is normally mounted to one surface, but then may stick to the other surface to creates a friction force between the surfaces. The force required to overcome the initial friction force may be greater than the resistive sliding forces between the surfaces. Therefore a relatively large force must be applied to initially move one of the surfaces, but once the surface moves the resistive sliding friction force is much less than the applied force. 
     This phenomena makes moving the surfaces relatively difficult because the surface will generally over-shoot the desired location because of the immediate decrease in resistance. This commonly results in erratic, choppy or segmented movement. This problem is not as significant with two-position valves because they are only going between extreme positions of open and closed and generally can not over-shoot these positions. However, this problem is of much greater concern for modulating valves that require relatively precise movement. In the preferred embodiment, wear rings overcome the “stick/slip” problem. 
     In the preferred embodiment, there are wear rings  100 ,  108  that accompany the O-rings  104 ,  112 . There is preferably a chamber wear ring  108  around the chamber surface  52  adjacent the chamber O-ring  112 , and a retainer wear ring  100  around the retainer surface  48  adjacent the retainer O-ring  104 . The wear rings  100 ,  108  preferably smooth the movement of the piston  40  and offer improved abrasion qualities to extend the life of the inlet valve  10 . The static friction force is reduced by the wear rings  100 ,  108  and the O-rings  104 ,  112  are preferably prevented from sticking to the opposite surface. A wear ring is not necessary for the auxiliary O-ring  114  because the piston retainer  60  normally does not slide relative to the piston chamber  22 .