WO2001038737A1

WO2001038737A1 - Compressor reed valve

Info

Publication number: WO2001038737A1
Application number: PCT/US2000/031815
Authority: WO
Inventors: Jeffrey W. Bergner
Original assignee: Thomas Industries Inc.
Priority date: 1999-11-23
Filing date: 2000-11-17
Publication date: 2001-05-31
Also published as: AU1780001A

Abstract

A gas pump valve has a flapper (58) with a distal end (62) that extends beyond the port (12) by at least .283 times the length of the flapper (58) from its bending point to the distal end (62). A separate land (54) is provided to support the tip of the distal end of the flapper.

Description

COMPRESSOR REED VALVE

CROSS REFERENCE TO RELATED APPLICATIONS Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT Not applicable.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to flapper or reed valves, and in particular to such intake and exhaust valves that are used in gas pumps such as compressors and vacuum pumps for air and other gases.

DISCUSSION OF THE PRIOR ART

Flapper valves, sometimes referred to as reed valves, for gas pumps typically have a thin layer of sheet metal which forms a reed or flapper which opens or closes in response to a pressure difference across it. For intake valves, this allows for the intake of gas to the working chamber on the intake stroke of the pump and for exhaust valves, the expulsion of gas from the working chamber on the exhaust stroke, during the pumping process.

One intake and one exhaust valve are typically provided on a valve plate which is between the working chamber of the pump and a head of the pump which is divided into intake and exhaust chambers. The intake flapper is provided over the intake port on the working chamber side of the plate and the exhaust flapper is provided over the exhaust port on the head side of the plate. Fasteners or other suitable means are provided to secure both flappers to the valve plate, a distance from the respective intake or exhaust port. Each flapper flexes to open and seals against a land which is provided around the respective port.

These valves act rapidly, each one opening and closing for each full cycle of the pump. Such pumps make noise when they operate, and there's been a long and ongoing effort in the industry to reduce the noise produced by such pumps. The present invention is directed toward reducing this noise.

Some of the noise associated with pumps is attributable to the flapper valves. Fig. 7 is a top plan view of the valve pad portion of a prior art valve plate surrounding a port 12, which may be either an intake port or an exhaust port. A valve flapper 14 is illustrated in phantom. The valve pad has lands 16 and 18 which support flapper 14 and a screw hole 20 is provided for a self tapping screw to be threaded into the valve plate to secure the flapper 14. Areas 22 of the pad are depressed to a depth of approximately .005 inches deep relative to the top, valve seating surfaces of the lands 16 and 18 and the surrounding surface 28 of the valve plate. Area 24 is depressed from the seating surfaces of the lands 16 and 18 and surface 28 to a depth of approximately .015 inches deep. The area 24 acts as a dirt trap to prevent dirt from being lodged underneath the flapper 14, which would interfere with the operation of the flapper 14. Typically, the flapper 14 is made from a thin (e.g. .003 or .004 inch thick) piece of sheet metal (e.g.. stainless steel) and may be formed with a slight curve so that it is biased against the land 16 so as to normally seal the port. The lands 16 and 18 would normally be at approximately the level of the surface 28 of the valve plate outside of the depressed areas 22 and 24.

Referring to Fig. 9, the flapper 14 is typically attached to the valve plate 30 with a dynamic backer 67 and a keeper strip 69 between the head of the screw 37 and the top of the flapper 14. As is known, the dynamic backer 67 may be made of any suitable resilient material, for example .014 inch thick resilient plastic, or the same material as the flapper 58, thin (e.g., .003 or .004 inch thick) stainless steel strip. The dynamic backer 67 acts like a leaf spring to help dampen valve flutter and improve dynamic response of the flapper 14. The dynamic backer 67 may not be necessary on either the intake or exhaust valve. The keeper strip 69, on the other hand, is a rigid strip of steel or other rigid material which does not bend with the flapper 14 but keeps it flat against the valve plate 30 in the area the bottom of the strip 69 overlies and contacts when the flapper is closed. The end 71 of the keeper strip 69 is rounded so as to relieve stress on the flapper 58 as the flapper 58 and dynamic backer 67 bend up against it. Thus, bending of the flapper 58 starts at the bottom of the end 71 , at the corner where the end 71 joins the flat bottom surface of the keeper strip 69. It is from this corner, referred to as the bending point, that the length L₂ discussed below is measured from. Although valves of the type shown in Figs. 7 and 9 perform their function well, they are relatively loud in general, and vary significantly from unit to unit in the sound volume produced. The present invention improves upon the valve design shown in Fig. 7, to result in pumps which are on average quieter than previous pumps and which vary less in the sound volume produced.

SUMMARY OF THE INVENTION

The invention provides a gas pump valve with a flapper which significantly overhangs the port on the side of the port opposite from where the flapper is secured to the valve plate. This change has been found to reduce the average volume of sound produced by pumps incorporating valves of the invention, and to reduce the variability in the volume of sound produced from one pump to another.

To accomplish the objectives of the invention, the valve flapper overhangs the port by at least .283 times the length of the flapper from where it starts bending when opening to the distal side of the port. At ratios below .283, the results are generally louder and erratic. Above .283, sound levels drop off dramatically and more consistently.

In a preferred form, a land is provided which supports the end of the flapper which overhangs the port. This is provided so as to support that end and prevent bowing of the flapper away from the port by the overhanging end bowing down at times when the flapper should be closed. These and other objects and advantages of the invention will be apparent from the detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a valve plate incorporating a valve pad of the invention on the intake valve side of the plate; Fig. 2 is a plan view of the intake valve side of the valve plate of Fig. 1 ;

Fig. 3 is a plan view of the exhaust valve side of the valve plate of Fig. 1; Fig. 4 is an enlarged plan view of the valve pad area used on either side of the valve plate of Figs. 1-3 with the flapper phantomed in;

Fig. 5 is a plan view of a valve flapper for the valve pad of Fig. 4; Fig. 6 is a side plan view of the valve flapper of Fig. 5; Fig. 7 is a view like Fig. 4 of a prior art valve pad with the outline of a flapper phantomed in;

Fig. 8 is a graph of empirical results showing the relationship of sound level to a ratio of valve overhang to valve length for a number of pressures; and Fig 9 is a cross-sectional view through a prior art valve and valve plate, showing the thickness of the flapper, dynamic backer and keeper strip enlarged for visual clarity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Fig. 1 illustrates a valve plate 30 of the invention. The intake valve side of the valve plate 30 is shown in Figs. 1 and 2 and the exhaust valve side is shown in Fig. 3. Each side has a valve pad 32 of the same configuration, but different position and orientation, which is shown in detail in Fig. 4. Insofar as the present invention is concerned, the valve plate 30 differs from prior art valve plates only by the valve pad 32 employed on each side of the valve plate.

Referring to Fig.4, a valve pad 32 of the invention includes a port 12 which extends all the way through the valve plate. On one side of the port 12, a blind screw hole 20 is formed to receive a thread forming screw 37 shown in phantom which is used to secure the valve flapper to the valve pad 32, specifically to land 18. Lands 16 and 18 surround the respective port 12 and screw hole 20 and dust trap recess 46 is formed around the lands 16 and 18. The pads 16 and 18 are at the level of the valve plate surface 50 surrounding the pad 32 and the recess 46 is approximately .015 inches recessed from the land surfaces 16 and 18. The recesses 42, 44 and 48 are approximately .005 inches recessed from the surfaces 16 and 18.

In the embodiment disclosed, the valve mount consists of a fastener 37 threaded into the hole 20, and the land 18 which supports the mounted end of the flapper. On the side of the port 12 opposite from the valve mount 52, a third land 54 is formed at the level of the lands 16 and 18.

Flapper 58 is drawn in phantom in Fig. 4 in the position in which it would be closed over the port 12. In this position, the half circular land 54 supports the overhanging end 60 of flapper 58. This prevents end 60 from moving further toward the valve plate than it should, which would result in bowing of the flapper 58 over the port 12 and undesired opening or leakage of it. Figs. 5 and 6 show the flapper 58 alone. The flapper 58 has a hole 66 through which fastener 37 is inserted and threaded into the hole 20 in the pad 32, to secure a keeper strip 69 and optional dynamic backer 67 on top of the flapper 58 (as shown in Fig 9), and secure the flapper 58. In the preferred embodiment, the dynamic backer 67 is only provided on the exhaust valve, not on the intake valve. A keeper strip 69 is provided for both valves. In the intake valve, the keeper strip bears directly against the valve flapper. A notch 68 may be formed along one side edge of the flapper 58, particularly if the flapper 58 is formed with an arch as shown in Fig. 6. In that case, the notch 68 tells an assembler which way the arch goes, since the depth of the arch may be so small that it is barely perceptible. The flapper 58 is assembled with its convex side facing away from the valve plate, so that it is flattened and biased against the lands 16 and 54. The material of the flapper 58 is the same as the material of the prior art flapper, for example .003 inch thick stainless steel.

In the preferred embodiment, the distance from the centerline of hole 20 to the center of port 12 is nominally .75 inches. The distance from the centerline of mounting hole 20 to the distal end 60 of the flapper 58 is nominally 1.250 inches as measured in the flat position of the flapper 58. The port 12 is .312 inches in diameter nominally and the width of the flapper is .438 inches nominally. The pad 18 typically has outer dimensions of .44 x .44 inches. These dimensions result in the flapper 58 overhanging the port 12 by a distance L,, illustrated in Fig. 4, of .344 nominally. This overhanging portion of flapper 58, measured from the side of port 12 which is distal from mount 20 to tip 60 and represented by distance L,, is referred to herein as the distal end 62 of the flapper 58. These dimensions also result in the distance L₂, which is from the bending point to the distal side of the port 12, being .686. The length L₂ of flapper 58 is referred to herein as the flex portion 64 of the flapper 58 and the length L, is referred to as the distal end 62. This results in a ratio of L,/L₂, the ratio of the length of the distal end 62 to the flex portion 64, of approximately .50, in the embodiment of Fig. 4.

The ratio of L,/L₂ is important to reduce the sound produced by operation of the flapper. Fig. 8 illustrates a graph of this ratio to sound volume for pressures of 10, 20 and 30 psig and for free flow. At L,/L₂ ratios of less that .283, the results are erratic and unpredictable. At an Lj/L₂ ratio of .283, sound levels begin to consistently lower, and each pressure curve remains relatively constant as the Lj/L₂ ratio increases further. Thus, an important aspect of the invention is to provide a flapper type valve in a gas pump in which the L,/L₂ ratio is .283 or greater.

A preferred embodiment of the invention has been described in considerable detail. Many modifications and variations will be apparent to those in the art. For example, it would not be necessary to use a dynamic backer or keeper strip to practice the invention.

Therefore, the invention should not be limited to the embodiment described, but should be defined by the claims which follow.

Claims

We claim:

1. In a gas pump valve having a valve pad and a valve flapper, the valve pad having a mount and a port spaced from the mount, and the valve flapper having a mounting area which is fixed to the mount, a flex portion of a certain length which extends from the bending point of the flapper, over the port and to the far side of the port, and a distal end of a certain length which extends from the flex portion beyond the port to a distal end tip, the improvement wherein the ratio of the length of distal end to the length of the flex portion is at least .283.

2. The improvement of claim 1 , wherein the valve pad includes a support land beneath the distal end of the flapper.

3. The improvement of claim 2, wherein the support land is spaced from the port.

4. The improvement of claim 2, wherein the support land is beneath the distal end tip.