Muffler with integral check valve

An unbiased valve is located within a muffler. The valve is positioned by the pressure differential across the valve and is either in the full open or full closed position. A pressure equalization tube is provided between the downstream cavity of the muffler and the back of the valve such that flow pattern produced low pressure areas are avoided and the valve can react to actual pressure differentials in the flow.

BACKGROUND OF THE INVENTION 
Positive displacement compressors have a pulsed output as trapped volumes 
are delivered to discharge. Mufflers are normally provided to reduce the 
noise generated as a result of the gas pulsations. When the compressor is 
initially shut off, there is a pressure differential across the compressor 
that tends to equalize through the compressor rather than through the 
refrigeration or air conditioning system. To prevent the reverse operation 
of the compressor as an expander without load, a check valve is normally 
provided in the compressor discharge to prevent reverse flow and 
operation. It is often a problem locating the check valve in an 
appropriate location and, if the valve is biased closed, it may move 
responsive to the pulsed output and thereby contribute further noise. 
SUMMARY OF THE INVENTION 
A flow responsive, unbiased valve is provided in the muffler and coacts 
with the inlet to the muffler to block return flow from the muffler to the 
compressor upon the occurrence of a condition tending to produce reverse 
flow such as shutting off the compressor. 
It is an object of this invention to prevent reverse flow of compressed gas 
within the confines of a discharge gas pulsation muffler. 
It is another object of this invention to prevent backflow of compressed 
gas through a compressor. These objects, and others as will become 
apparent hereinafter, are accomplished by the present invention. 
Basically, a valve is provided which is located in a muffler and positioned 
responsive to flow without a return bias. The valve provides a smooth 
profile in the opening direction and a flow resisting profile in the 
closing direction.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In FIG. 1, the numeral 20 generally designates a muffler with an internal 
check valve which is sealingly connected to the discharge of a screw 
compressor 10. Muffler and check valve 20 includes a housing made up of a 
first portion 22 and a second portion 24 which are sealed together with 
partition or baffle plate 26 secured therebetween and defining an inlet 
cavity 30 with first portion 22 and a outlet cavity 32 with second portion 
24. Portion 22 is secured to compressor 10 and has an inlet passage 22-1 
connected to discharge passage 10-1 of compressor 10. Inlet passage 22-1 
terminates in valve seat 22-2. 
As best shown in FIG. 2, valve guide stem 28 is fixedly received in bore 
24-1, surrounded by spacer 34, and extends through partition 26 into 
cavity 30. Referring back to FIG. 1, valve guide stem 28 extends into bore 
40-1 of valve 40. A plurality of muffler tubes 42 are secured in partition 
or baffle plate 26 and provide a fluid path between inlet cavity 30 and 
outlet cavity 32. As best shown in FIG. 3, muffler tubes 42 are arranged 
in an arcuate pattern over a portion of a circle such that none of the 
muffler tubes 42 is directly aligned with outlet 24-2 and are only tokenly 
overlain by valve 40. Muffler tubes 42 are identical and have the same 
radial spacing. Pressure equalization tube 44 is located radially inward 
of muffler tubes 42 so as to be completely overlain by valve 40 while not 
being directly aligned with outlet 24-2. 
In operation valve 40 is slideable on valve guide stem 28 responsive to 
flow/pressure differential across valve 40. As illustrated in FIG. 1, 
valve 40 is in the fully open position and hot pressurized gas compressed 
in the compressor 10 serially flows through discharge passage 10-1, inlet 
passage 22-1 and over valve 40 into inlet cavity 30. Valve 40 overlies one 
end of pressure equalization tube 44 so that flow from inlet cavity 30 to 
outlet cavity 32 is via muffler tubes 42. Because muffler tubes 42 are not 
aligned with outlet 24-2, there is a reverberation in the flow in cavity 
32 before the flow passes through outlet 24-2 to the refrigeration or air 
conditioning system. Pressure equalization tube 44 communicates the 
lower/downstream pressure of chamber 32 to the back side of valve 40 so 
there is no tendency for closing valve 40. In contrast, pressure 
pulsations produce chatter when conventional valves react to the changing 
pressure differential and start moving towards closing and back towards 
opening. 
If the compressor 10 is shut off, the refrigeration or air conditioning 
system will tend to equalize through compressor 10. Flow will go from 
cavity 32, through muffler tubes 42 into cavity 30, over valve 40 and into 
passage 22-1 and back into compressor 10 via passage 10-1. But for the 
presence of pressure equalization tube 44, flow over valve 40 would 
produce a low pressure area behind valve 40 such that it would tend to 
remain open under reverse flow. Pressure equalization tube 44 communicates 
the cavity 32 pressure with the area behind valve 40 and the resultant 
pressure differential across valve 40 causes valve 40 to close upon 
conditions of reverse flow. 
Although a preferred embodiment of the present invention has been 
illustrated and described, other modifications will occur to those skilled 
in the art. It is therefore intended that the present invention is to be 
limited only by the scope of the appended claims.