EP0807209A1

EP0807209A1 - Protection device for a high side co-rotating scroll compressor

Info

Publication number: EP0807209A1
Application number: EP95944413A
Authority: EP
Inventors: Robert E. Utter; Joe T. Hill; Charles A. Singletary
Original assignee: Alliance Compressors Inc
Current assignee: Alliance Compressors Inc
Priority date: 1995-02-03
Filing date: 1995-12-15
Publication date: 1997-11-19
Also published as: WO1996023976A1; AU4647096A; JPH10513523A; CA2211688A1

Abstract

A high side co-rotating refrigerant scroll compressor having an oil sump (64) in the discharge pressure portion (20) of its shell is protected from the abnormal conditions of high discharge pressure and reverse direction scroll rotation by a normally closed valve arrangement (74, 75) which defines a flow path that selectively opens into the suction pressure (22) or discharge pressure portion of the compressor shell dependent upon the nature of the abnormal operating condition. The valve arrangement includes a standoff portion which permits the valve arrangement and the flow path it defines to traverse the oil sump and open into the discharge pressure portion of the shell at an elevation above the level of oil in the sump.

Description

D E S C R I P T I O N

Title

PROTECTION DEVICE FOR A HIGH SIDE CO-ROTATING SCROLL COMPRESSOR

Background of the Invention

This invention pertains generally to scroll apparatus and more specifically to scroll compressors of the co-rotating type wherein both scroll members rotate on parallel, offset axes. With still more particularity, this invention relates to the protection high-side co-rotating refrigerant scroll compressors against damage due to the occurrence of abnormal compressor operating conditions by the opening of a secondary gas flow path between the suction and discharge pressure portions of the compressor shell when such conditions occur.

Scroll compression apparatus typically comprises two scroll members each of which has an involute wrap. The wraps of the scroll members extend from an end plate and are in an interleaved relationship. Relative orbital motion of one scroll member with respect to the other causes the creation of a series of pockets between the scroll wraps which, in operation, decrease in volume and compress any gas trapped therein. Scroll compressors are typically of a first type in which one of the scroll members is fixed while the other orbits thereabout or of the second, so-called "co-rotating" type in which both scroll members rotate on parallel but offset axes. In a co-rotating scroll compressor, one of the scroll members is characterized as the drive scroll and the other as the idler scroll. The drive scroll member is driven through a drive shaft which extends from its end plate and is fixedly coupled for rotation with the rotor of the motor which drives the compressor.

Hermetic compressors (compressors in which both the drive motor and compression mechanism are disposed in a hermetic shell), including those of the scroll type, are categorized as being of a high side or low side design. A high side compressor is one in which the drive motor is disposed in the portion of the compressor shell which is at compressor discharge pressure when the compressor is in operation. A low side compressor is one in which the drive motor is disposed in the portion of the compressor shell which is at suction pressure when the compressor is in operation.

It has prospectively been determined, with respect to hermetic co-rotating scroll compressors, to be advantageous to employ a high side design in which the compressor drive motor is disposed physically above the compression mechanism and in which the drive scroll member drive shaft is used to communicate compressed refrigerant gas out of the compression mechanism to the discharge pressure portion of the compressor shell. Exemplary in that regard are U.S. Patents 4,927,339 and 5,080,566, the former being assigned to the assignee of the present invention and being incorporated herein by reference. It has also been prospectively determined that in such a compressor it is advantageous to collect oil in a sump in the discharge pressure portion of the compressor shell so that discharge pressure can be used to drive the oil collected therein to the various locations within the compressor requiring lubrication.

It is also necessary, however, to protect compressors, including those of the high side co-rotating scroll type, against certain abnormal operating conditions, including the condition where the compressor runs backwards, as might occur if it is miswired, and the condition where the pressure in the discharge pressure portion of the compressor shell exceeds a predetermined maximum, such as might be occasioned by the failure of a component downstream of the compressor in an air conditioning or refrigeration system in which the compressor is employed. In each such case, provision of an alternate, normally closed gas flow path between the suction and discharge pressure portions of the shell, other than the normal refrigerant gas flow path through the compression mechanism, becomes necessary.

While the use of valves of the check valve or pressure relief types to communicate gas between the suction and discharge pressure portions of a scroll compressor during abnormal compressor operating conditions is known, see for example U.S. Patents 4,560,330; 4,767,293; 4,840,545 and

5,186,613, the creation of a flow path between the suction and discharge pressure portions of a high side co-rotating scroll compressor, where the discharge pressure portion of the compressor shell defines an oil sump which must be traversed by the alternate gas flow path, presents difficulties and requires solutions not contemplated in the prior art. There is therefore a need for a viable arrangement in a high side co-rotating scroll compressor, where the compressor includes a discharge pressure portion disposed vertically above a suction pressure portion and where the discharge pressure portion defines an oil sump, by which to provide a selectively openable alternate gas flow path between the suction and discharge pressure portions of the compressor in order to protect the compressor against abnormal compressor operating conditions.

Summary of the Invention

It is an object of the present invention to provide for the protection of a high side co-rotating scroll compressor against abnormal compressor operating conditions.

It is a further object of the present invention to provide for the protection of a high side hermetic co-rotating scroll compressor against the existence of compressor discharge pressures greater than a predetermined maximum and against the condition where pressure in the discharge pressure portion of the compressor shell comes to be less than the pressure in the suction pressure portion of the shell.

It is a still further object of the present invention to provide for the protection of a high side co- rotating scroll compressor against abnormal compressor operating conditions by the provision of a alternate gas flow path between the discharge pressure portion and suction pressure portions of the compressor shell where such path must traverse an oil sump defined by the discharge pressure portion of the compressor shell. These and other objects of the present invention will become apparent when the attached drawing figures and following Description of the Preferred Embodiment are considered. In the present invention, gas compressed in the compression mechanism of a high side co-rotating scroll compressor is discharged into the discharge pressure portion of the compressor shell through the shaft by which the drive scroll member is driven by the compressor drive motor. The compressed gas discharged from the compression mechanism carries with it entrained lubricant which is separated for further use within the compressor prior to the discharge of the compressed gas from the compressor. Such disentrained lubricant drains to a sump defined at the bottom of that portion of the compressor shell. In such an arrangement, both the oil sump and the frame within the compressor shell which separates the discharge from the suction pressure portions of the compressor must be traversed by the alternate gas flow passage used to communicate gas from one portion of the shell to the other upon the occurrence of abnormal pressure-related compressor operating conditions. If that sump were not traversed by the alternate gas flow path and the drainage of oil therethrough were permitted to occur when the path opened, the primary supply of oil to compressor bearing surfaces might be depleted to the extent that bearings and other surfaces which are normally lubricated with lubricant from that sump come to be inadequately lubricated or lubricated not at all for too long a period of time. In such an instance, catastrophic damage to the compressor could occur even as the compressor is being protected from the occurrence of the pressure-related abnormal compressor operating conditions. In a first instance, by disposing a valve between the suction pressure and discharge pressure portions of the shell so as to provide an alternate gas flow path which opens into the suction pressure portion of the shell to permit the flow of gas from the discharge to the suction pressure portion while preventing the drainage of oil therethrough, abnormally high pressure in the discharge pressure portion of the shell is relieved providing time for the compressor, and therefore the refrigeration system in which it is employed, to shut down prior to the occurrence of permanent damage to the compressor. At such time as the system condition causing high discharge pressure to develop is remedied the gas flow relief path is closed and the compressor and system operate normally.

In a second instance, where the compressor is miswired so that it is caused to run backwards with the result that the pockets defined between the scroll wraps, instead of moving radially inward and decreasing in volume, move radially outward and expand in volume in a pumping action, the compression mechanism acts as an expander. The source for gas in such an instance is the portion of the compressor shell to which the compression mechanism would normally discharge. The expansion of the pockets defined by the scroll members under this circumstance can cause low and even negative pressures to develop within the pockets to the extent that insufficient or no source of gas is available in what would normally be the discharge pressure portion of the compressor for the compression mechanism to pump from. As a result, the scroll members can be drawn tightly together which can lead, to the extent the scroll members continue to rotate, in severe damage to the scroll members. By disposing a valve between the suction and discharge pressure portions of the shell to provide an alternate gas flow path which opens into the discharge pressure portion of the shell to permit the flow of gas thereinto from the suction pressure portion of the shell, it is ensured that the compressor, under the circumstance described, will always have a supply of gas from which to pump until such time as the compressor is shut down.

In order to ensure that the alternate gas flow path between the suction pressure portion and the discharge pressure portion of the shell is not occluded or gas flow slowed by the oil in the sump in the discharge pressure portion of the shell under either of the circumstances described above, the opening of the alternate gas flow path into the discharge pressure portion of the shell is at a height which is above the level of oil in the sump.

Description of the Drawing Figures

Figure 1 is a cross-sectional view of a high side co-rotating scroll compressor incorporating the protective arrangement of the present invention. Figure 2 is an enlarged portion of Figure 1 more clearly illustrating the compressor protective apparatus and the nature of its installation in the compressor of Figure 1. Figures 3 and 4 schematically illustrate how the separate protective valves of the embodiment of Figures 1 and 2 can be combined into a single valve arrangement which accomplishes the same purpose. Description of the Preferred Embodiment

Referring first to Figures 1 and 2, co-rotating scroll compressor 10 is comprised of an upper shell portion 12, a middle shell portion 14 and a lower shell portion 16 all of which are sealingly connected to form a hermetic shell 18. Shell 18 is divided into a discharge pressure portion 20 and a suction pressure portion 22 by a central frame 24. Suction gas is communicated into suction pressure portion of shell 18 through suction fitting 25.

Disposed in suction pressure portion 22 of compressor 10 is an idler scroll member 26 and a drive scroll member 28. The drive and idler scroll members comprise the compression mechanism of co-rotating scroll compressor 10. Drive scroll member 28 is comprised of an end plate 30 from which an involute wrap 32 extends in a first direction and from which a drive shaft 34 extends in the opposite direction. End plate 30 defines a discharge port 36 which is in flow communication with a discharge passage 38 defined in the drive shaft 34 of the drive scroll member.

Motor 39 has a rotor 40, which is penetrated by and fixedly attached to drive shaft 34 of the drive scroll member, and a stator 42 which is fixedly mounted in the discharge pressure portion 20 of compressor shell 18. A gap 44 is defined between rotor 40 and stator 42. Drive shaft 34 is rotatably carried in middle bearing housing 46 of central frame 24 within shell 18.

Upper frame 48 of compressor 10 includes an upper bearing housing 50 in which distal end 52 of drive shaft 34 is rotatably carried. Mounted on upper frame 48 is an oil separator dome 54 which is penetrated by an internal overload device 56. Upper frame 48 defines a first series of apertures 58 through which discharge gas issuing from passage 38 of drive shaft 34 passes as well as a second set of apertures 60 through which discharge gas passes prior to exiting upper shell portion 12 of the compressor through discharge fitting 62.

Defined in discharge pressure portion 20 of compressor 10 immediately above central frame 24 is discharge pressure oil sump 64. Oil from sump 64 is provided to bearing surface 66 of middle bearing housing 46 through oil passage 68. A shaft seal 70 may be mounted in middle bearing housing 46 so as to sealingly surround drive shaft 34.

Middle bearing housing 46 also defines a first passage 72 and a second passage 73 which communicate between discharge pressure portion 20 and into suction pressure portion 22 of compressor 10. Passages 72 and 73 are preferably at least partially threaded. An internal pressure relief valve 75 is threaded into first passage 73 while a check valve 74 is threaded into second passage 72. Also defined by central frame 24 is an oil passage 76 which communicates with a circumferential oil passage 78. Passage 78 is preferably at least partially defined by shell 18 and supplies oil, as will further be described, from sump 64 to passage 92.

Idler scroll member 26 has an end plate 80 from which involute wrap 82 extends in a first direction and from which a stub shaft 84 extends in the opposite direction.

Involute wrap 82 of idler scroll member 26 is in interleaved engagement with involute wrap 32 of drive scroll member 28 and cooperates therewith to define discharge pocket 85 which is in flow communication with discharge port 36. An Oldham coupling 86 maintains the relative angular orientation of the wraps of the scroll members in operation and drivingly couples the drive to the idler scroll member. Lower frame 88 is disposed in suction pressure portion 22 of shell 18 and includes an integral bearing housing 90 in which stub shaft 84 of the idler scroll member is rotatably accommodated. Lower frame 88 preferably defines an oil passage 92 which is in flow communication with circumferential oil passage 78 as well as space 94 defined by stub shaft 84 and lower bearing housing 90. The bearing surface of lower bearing housing 90 in which idler stub shaft 84 rotates is provided with lubricant driven from discharge pressure sump 64 through passages 76, 78 and 92 and space 94 by the discharge pressure to which sump 64 is exposed when compressor 10 is in operation and by the differential pressure across the bearing surface.

Referring additionally now to Drawing Figure 2 it will be appreciated that valves 74 and 75 are illustrated having components positioned as they are when compressor 10 is at rest or in normal operation. In that regard, during normal compressor operation discharge pressure portion 20 of shell 18 is filled with compressed refrigerant gas at discharge pressure. As indicated earlier, lubricant carried out the of the compression mechanism into discharge portion 20 within the compressed refrigerant gas is disentrained within discharge pressure portion 20 and drains to sump 64. As such, in addition to frame 24, lubricant in sump 64 is physically interposed between the refrigerant gas thereabove in discharge pressure portion 20 and suction pressure portion 22 of the compressor shell which, in operation, is filled with refrigerant gas at suction pressure. In operation, discharge pressure maintains ball element 96 of valve 74 seated over opening 98 therein effectively occluding passage 100 which would otherwise communicate between discharge pressure portion 20 and suction pressure portion 22 of shell 18. With respect to valve 75, ball member 102 is biased, such as by spring 104 to seat in opening 106 thereby occluding passage 108 during normal compressor operation.

It will be appreciated that spring 104 is selected such that its strength is sufficient to maintain ball 102 seated sealingly against opening 106 in the face of normal discharge pressures so as to occlude, like ball member 96 of valve 74, passage 108 which would otherwise provide a flow path between discharge pressure portion 20 and suction pressure portion 22 of the compressor shell. Upon the occurrence of an abnormal operating condition of the type which causes pressure in discharge pressure portion 20 of shell 18 to increase to an extent sufficient to create a pressure differential which overcomes the opposing force of spring 104 in combination with the force exerted by suction pressure on ball 102, and to dislodge ball 102 from opening 106, passage 108 opens for flow thereby relieving the overpressure in discharge pressure portion 20. Ball 102 remains dislodged and passage 108 remains open until such time as the abnormal system or compressor operating condition abates or the compressor is shut down and the biasing force of spring 104 comes to be sufficient to cause ball 102 to seat in opening 106 against the pressure in the discharge pressure portion of the shell. Upon the occurrence of an abnormal operating condition of the type wherein the pressure in suction pressure portion 22 of the compressor shell becomes greater than the pressure in discharge pressure portion 20, ball 96 of valve 74 is similarly caused to be unseated thereby opening passage 100 for flow between the suction pressure and discharge pressure portions of the shell. When ball 96 is carried out of opening 98 it is trapped by crossbar 110 within valve 74 without occluding or excessively limiting flow through passage 100. Ball 96 reseats by force of gravity and discharge pressure at such time as the pressure in the discharge pressure portion of the shell comes to exceed the pressure in suction pressure portion 22 (the normal compressor operating condition) .

It will be appreciated that under the circumstance of there being an abnormally high discharge pressure in discharge pressure portion 20 of the compressor shell the abnormally high discharge pressure serves only to more sealingly seat ball 96 in opening 98 in valve 74 while opening valve 75 for flow. Under the circumstance where the pressure in suction pressure portion 22 of the compressor shell exceeds the pressure in discharge pressure portion 20, the higher pressure in the suction pressure portion of the shell serves to assist spring 104 in maintaining ball 102 seated in opening 106 while carrying ball 96 out of opening 98 to open valve 74 for flow. Crossbar 110, which serves to trap ball 96 when it is dislodged from opening 98 is best illustrated in Figure 4. Turning now to Figures 3 and 4, an alternative embodiment of the protective valve apparatus of the present invention is illustrated. It will be appreciated that in the embodiment of Figure 4 the individual valve members 74 and 75 of the embodiment of Figures 1 and 2 are replaced by a single valve assembly 170 which incorporates the components of the two valve members discussed above. As is illustrated, valve assembly 170 is a unitary member which is threaded into or otherwise secured, such as by welding or brazing, in opening 172 of frame 24 and has first and second arm portions 174 and 175 which connect into a single depending portion 176.

Portion 176 of assembly 170 is ensconced in passage 172, there being a requirement for only one passage through frame 24 in the embodiment of Figures 3 and 4 for this purpose. It will be appreciated that assembly 170 could likewise be configured so as to have dual openings into suction pressure portions of the shell and a single opening into the discharge pressure portion. That configuration would, however, require the definition of two passages through frame 24. It is also to be noted that in the embodiment of Figure 4, ball 96 is illustrated as being in its unseated position, trapped by crossbar 110, as would be the case when the pressure in suction pressure portion 22 of shell 18 is relieving to discharge pressure portion 20 thereof. As will be appreciated with respect to the embodiments of both Figures 1 and 2 and Figures 3 and 4, the portion of valves 74, 75 and valve assembly 170 between the upper surface of frame 24 and the surface of the oil in sump 64 can be characterized as a "standoff" portion the purpose of which is to elevate the openings of the valve and valve assembly to a height above the oil level in sump 64. The protective apparatus of the present invention is unique, in that regard, in its ability to provide for a secondary, alternate gas flow path between the discharge pressure portion and suction pressure portions of a compressor shell where an oil sump is required to be traversed by such flow path. In the absence of a standoff, oil in sump 64 would prevent or restrict gas flow and/or would potentially drain through the flow path when opened thereby setting the compressor up for a still different mode of failure predicated on a lack of lubrication.

While the present invention has been described in preferred and alternative embodiments by which to define a secondary flow path between the suction pressure portion and discharge pressure portions of a scroll compressor through an intervening oil sump, it will be appreciated that there are alternatives thereto, with respect to the nature of the protective relief valves themselves, their configuration and the manner in which such valves open to flow under the abnormal pressure related circumstance. In any event, the present invention contemplates the traversal of an oil sump by gas flow passage defining apparatus in order to permit the flow of refrigerant gas, by an alternate path and for pressure relief purposes, between what normally are the suction and discharge pressure portions of a compressor shell to protect the compressor under the circumstance of the development of abnormal pressure-related operating conditions.

Claims

C L A I M S

1. A scroll compressor comprising: a hermetic shell, said shell divided into a suction pressure portion and a discharge pressure portion, said discharge pressure portion defining a lubricant sump; a first scroll member, said first scroll member being mounted for rotation in said suction pressure portion of said shell; a second scroll member, said second scroll member being mounted for rotation in said suction pressure portion of said shell, said first and second scroll members comprising a compression mechanism and being cooperatively engaged for concurrent rotation on parallel, offset axes; and a protective valve, said valve defining a normally closed flow path between said suction pressure portion and said discharge pressure portion of said shell, said valve traversing said lubricant sump in said discharge pressure portion of said shell so as to open into said discharge pressure portion of said shell at an elevation above the surface of lubricant in said sump.

2. The scroll compressor according to claim 1 wherein upon the occurrence of an abnormal pressure condition in said shell, said abnormal condition causes said normally closed flow path defined by said protective valve to open.

3. The scroll compressor according to claim 2 wherein said compressor further comprises a frame, said frame dividing said shell into said suction pressure portion and said discharge pressure portion, said frame defining an opening and said protective valve being sealingly disposed in said opening.

4. The scroll compressor according to claim 3 wherein said valve has a unitary housing and defines first and second flow paths therethrough, said first flow path opening in response to the existence of pressure in said suction pressure portion of said shell which is greater than the pressure in said discharge pressure portion of said shell and said second flow path opening when the pressure in said discharge pressure portion of said shell exceeds the pressure in said suction pressure portion of said shell and a predetermined pressure differential therebetween is exceeded.

5. The scroll compressor according to claim 4 wherein said second flow path is occluded by a closure member during normal compressor operation, said closure member being biased so as to maintain said second flow path closed so long as said pressure differential between said discharge pressure portion of said shell and said suction pressure portion of said shell is not exceeded.

6. The scroll compressor according to claim 3 wherein said protective valve comprises a first protective valve and further comprising a second protective valve, said second protective valve defining a normally closed flow path between said suction pressure portion of said shell and said discharge pressure portion of said shell, said second protective valve traversing said lubricant sump in said discharge pressure portion of said shell so as to open into said discharge pressure portion of said shell at an elevation above the surface of lubricant in said sump.

7. The scroll compressor according to claim 6 wherein said first protective valve opens in response to the existence of pressure in said suction pressure portion of said shell which is greater than the pressure in said discharge pressure portion of said shell and wherein said second protective valve opens when the pressure in the discharge pressure portion of said shell exceeds the pressure in the suction pressure portion of said shell and a predetermined pressure differential therebetween is exceeded.

8. The scroll compressor according to claim 7 wherein said second protective valve includes a closure member, said closure member being biased to maintain said flow path defined by said second protective valve closed.

9. The scroll compressor according to claim 8 wherein said frame defines a second opening, said second protective valve being sealingly disposed in said opening.

10. The scroll compressor according to claim 9 wherein said first protective valve and said second protective valve each have a distal end, said distal end defining an opening, said standoff portion elevating said openings to a height above the surface of lubricant in said sump.

11. A method of protecting a scroll compressor against abnormal operating pressures which develop in the compressor shell comprising the steps of: defining a suction pressure portion in said shell; defining a discharge pressure portion in said shell vertically above said suction pressure portion; defining a lubricant sump at the bottom of said discharge pressure portion of said shell; defining a normally closed flow path within said shell, said normally closed flow path traversing said lubricant sump in said discharge pressure portion of said shell and opening into said discharge pressure portion of said shell at an elevation above the surface of said lubricant sump; and causing said normally closed flow path to open in response to the occurrence of an abnormal pressure condition in said shell.

12. The method according to claim 11 wherein said opening step comprises the step of opening said flow path, when the pressure in the discharge pressure portion of said shell exceeds the pressure in said suction pressure portion of said shell, in response to the development of a pressure differential between said discharge pressure portion of said shell and said suction pressure portion of said shell which exceeds a predetermined pressure differential.

13. The method according to claim 11 wherein said opening step further comprises the step of opening said path to flow when the pressure in said suction pressure portion of said shell exceeds the pressure in said discharge pressure portion of said shell.

14. The method according to claim 11 comprising the step of defining first and second openings for said normally closed flow path into one of said suction pressure portion and said discharge pressure portions of said shell, said normally closed flow path opening through said first opening when the pressure in said suction pressure portion of said shell exceeds the pressure in said discharge pressure portion of said shell and said normally closed flow path opening through said second opening in response to the development of a pressure differential between said discharge pressure portion of said shell and said suction pressure portion of said shell, when the pressure in the discharge pressure portion of said shell exceeds the pressure in said suction pressure portion of said shell, which exceeds a predetermined pressure differential.

15. The method according to claim 11 wherein said normally closed flow path comprises a first normally closed flow path and wherein said method comprises the further step of defining a second, independent, normally closed flow path between said suction pressure portion and said discharge pressure portion of said shell, said first normally closed flow path opening, when the pressure in the discharge pressure portion of said shell exceeds the pressure in said suction pressure portion of said shell, in response to the development of a predetermined pressure differential therebetween and said second normally closed flow path opening in response to the existence of pressure in said suction pressure portion of said shell which exceeds the pressure in said discharge pressure portion of said shell. 21

16. A co-rotating scroll compressor comprising: a hermetic shell, said shell having a frame, said frame dividing said shell into a suction pressure portion and a discharge pressure portion, said discharge pressure portion defining a lubricant sump; a first scroll member, said first scroll member being mounted for rotation in said suction pressure portion of said shell; a second scroll member, said second scroll member being mounted for rotation in said suction pressure portion of said shell, said second scroll member being drivingly coupled to said first scroll member for concurrent rotation therewith and said second scroll member having a drive shaft which penetrates said frame and extends into said discharge pressure portion of said shell, said first and said second scroll members comprising a compression mechanism, gas compressed by said compression mechanism being communicated thereoutof and into said discharge pressure portion of said shell through said drive shaft; a motor, said motor being disposed in said discharge pressure portion of said shell and being drivingly coupled to said drive shaft of said second scroll member; and a valve assembly, said valve assembly defining a normally closed flow path between said suction pressure portion and said discharge pressure portion of said shell, said normally closed flow path traversing both said frame and said lubricant sump in said discharge pressure portion of said shell so as to open into said discharge pressure portion of said shell at an elevation above the surface of lubricant in said sump.

17. The scroll compressor according to claim 16 wherein upon the occurrence of an abnormal pressure condition in either of said discharge pressure portion or said suction pressure portion of said shell, said normally closed flow path is caused to open.

18. The scroll compressor according to claim 17 wherein said valve assembly has a unitary housing and defines first and second flow paths therethrough, said first flow path opening in response to the existence of pressure in said suction pressure portion of said shell which is greater than the pressure in said discharge pressure portion of said shell and said second flow path opening, when the pressure in said discharge pressure portion of said shell is greater than the pressure in said suction pressure portion of said shell, in response to the development of a predetermined pressure differential therebetween.

19. The scroll compressor according to claim 18 wherein said second flow path is occluded by a closure member during normal compressor operation, said closure member being biased so as to maintain said second flow path closed so long as the pressure in said discharge pressure portion of said shell is less than said predetermined pressure differential.

20. The scroll compressor according to claim 16 wherein said valve assembly comprises a first valve assembly and further comprising a second valve assembly, said second valve assembly defining a normally closed flow path between said suction pressure portion of said shell and said discharge pressure portion of said shell, said normally closed flow path defined by said second assembly traversing both said frame and said lubricant sump in said discharge pressure portion of said shell so as to open into said discharge pressure portion of said shell at an elevation above the surface of lubricant in said sump.

21. The scroll compressor according to claim 20 wherein said first valve assembly opens in response to the existence of pressure in said suction pressure portion of said shell which is greater than the pressure in said discharge pressure portion of said shell and wherein said second valve assembly opens, under the circumstance that the pressure in said discharge pressure portion of said shell exceeds the pressure in said suction pressure portion of said shell, in response to the existence of a predetermined pressure differential between said suction pressure portion of said shell and said discharge pressure portion of said shell.

22. The scroll compressor according to claim 21 wherein said first and said second valve assemblies each include a closure member, said closure member of said second valve assembly being biased to maintain said flow path defined by said second valve assembly closed whenever the differential pressure between said discharge pressure portion of said shell and said suction pressure portion of said shell is less than said predetermined pressure differential and said closure member of said first assembly being maintained closed against a seat therein by compressor discharge pressure whenever the pressure in said discharge pressure portion of said shell is greater than the pressure in said suction pressure portion of said shell.