CA1054114A - Rotary compressor - Google Patents

Abstract

ABSTRACT

A rotary, sliding vane compressor is provided with means for supplying a relatively small, predetermined quantity of an incompressible fluid, such as lubricating oil, under-neath the vanes. The fluid is injected at a point while the vanes are collapsing within the vane pockets formed within the rotor and is trapped underneath the vane during its movement to the contact point thereby resisting the collapse of the vane so as to hold the vane tip in continuous engagement with the stator surface in the compression cavity. The means for supplying the fluid underneath said vanes includes a device for interrupting flow of lubricant from a sump to the interior of the compressor housing thereby controlling or metering the lubricant and also preventing reverse rotation of the compressor rotor caused by oil pressure under the vanes forcing the vane tips to follow the curvature of the cylinder wall in a backward direction. Means are also provided for relieving the suction created when the vanes move outwardly in their vane slots during startup and for draining any liquid trapped under the vanes. A relief groove is milled into the face of one of the end plates and affords communication between the vane slot and a zone of higher pressure fluid.

Description

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10541~

This invention relates to rotar~ sliding vane com-p~essors and more particularly to means for holding the vanes in proper engagement with the stator suxface or cylin-der wall so as to secure a gas seal between the vane tips and the cylinder surface and to prevent hoppiny or vibration which causes wear on the vanes and the cylinder wall. Such means include a system for supplying lubricant under pressure to the vane slots and means for positively interrupting the flow of lubricant to the compressor to meter the amount of oil available for delivery to the vane slots and also prevent reverse rotation of the rotor w~en the compressor is shut down. Another feature includes means for breaking the suction underneath the vanes which normally occurs at startup when the vanes begin to extend outwardly in the vane slots and for relieving liquid trapped under the vanes.

A wide variety of techniques have been used in the prior art to obtain continuous contact between the vane tips and the cylinder wall. One of the most common is the use of springs or other resilient elements which bias the vanes outwardly for this purpase. An example of this type of arrangement is found in U. S. Patent 2,816,702 issued to R. R. Woodcock on December 17, 1957. One of the de~iciencies is the tendency of the small springs required to break under the rapid expansion and contraction of the vane ~ithin the -~
vane slot. Still another technique, which is more closely related to the subject matter o~ the present invention, is to utilize oil at or near discharge pressure to maintain an outward thrust on the vane. This has the disadvanta~e of .. . .

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high vane loading at all times, creating wear when thc vanes -are passing through the suction area. ~n example of this - arrangement is found in U. S. Patent 2,846,138 issued to C. E. Racklyeft on August 5, 1958.
Still another arrangement which may hav~ possible utility in air compressors, as distinguished ~rom refrigeration compressors is described in U. S. Patent 3,434,655 issued to F. O. Bellmer on March 25, 1969. In Bellmer, gas is trapped underneath the vane to form an elastic pocket or "gas spring"
during the collapse of the vane inward during the compression phase of the cycle. At or near the contact point, the pressure is relieved until such point as the vane aga~n begins its inward or collapsing movement approaching the contact point.
Belgian Patent No. 516,611 also shows a gas compressor with a passage communicating with an undervane space; but said spaces are not filled with li~uid.
U. S. Patent 2,400,286 (Buckbee) describes a com- ;
pressor which is similar to Belgian 516,611 in that air is admitted to and trapped in the undervane spaces while U. S.
-Patent 2,522,824 (Hicks) employs oil to bias the vanes against the cylinde~ wall. The latter, however, has no means for controlling the flow of oil available to the undervane spaces.
U. S. Patents 2,653,551 (Rosaen) and 3,782,867 lGerlach et al) generally disclos~ trapping of fluid under the vanes in a rotary vane compressor.
U. S. Patent 3,649,140 issued to L. E. ~larlin on March 14, 1972 describes a rotary metering valve mechanism , v ~ ~v s ~I r~ ~

1054~L~4 ~ .
which is connected to the rotor such that lubricant flowing from the sump to the compressor is caused to enter into a chamber provided by a bore in the metering valve. When the r valve is rotated a predetermined distance it registers with an outlet where the lubricant is then caused to flow to the compressor cavity. In this manner, the flow of oil is pre-vented during occasional reverse rotation of the compressor rotor caused by the equalization of the pressure differential between suction pressure and discharge pressure. In systems where the oil is supplied under the vanes, the tendency for reverse rotation to occur is caused by another factor. The pressure of oil forces the vane tip against the cylinder wall in the zone between closed suction and discharge~ In order to relieve the pressure, the vane tip slides in a direction toward a larger diameter i.e. away from the contact point toward suction. This causes the rotor to move in a reverse direction. Since Harlin (U.S. 3,649,140) is supplying oil primarily to the compression cavity and the side faces of the rotor, there is no entrapment of liquid ;~
under the vanes and no cus~ioning effect.
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Additional prior art showing various means for supplying lubricating oil to the compressor throug~ ports communicating with the compression cavity are: U. S. patents to Galin 3,056,542 (passage 52); Kosfeld 2,988,267 (passage 37j;
Sadler 2,929,550 (passage 31); and Clerc 2,634,904 (passage 86). None of the above provide an interrupter ele~ent driven by the rotor drive shaft for intermittently blocking flow of oil to the undervane spaces and thereby metering or 07404~-~-Y , i~S4114 controlling the flow to the undervane spaces as the ~nique zone to which oil is directed.
The use of undervane spaces, and the vanes as pumping mechanisms, for supplying lubricant to various parts of a rotary sliding vane compressor is well known. In U. S.
Patent 3,~80,204 issued to L. E. Harlin on November 25j 1969 there is provided a passage which perlodically registers with the undervane spaces, at a position adjacent the suction zone, to draw lubricant from the area around the bearing and seal, and thereby create a low pressure zone in such area.
This causes the oil circulating inside the compressor housing ' , to migrate to the low pressure zone and provide adequate lubrication to the bearing and seal.
British Patent 692,257, shows a compressor,in which oil is admitted under the vanes as they are moving outwardly and conducts the oil to one of the bearings (and seals) during 'the inward movement of the vanes. A return '- ' passage is also provided so that the oil passing back from the bearing cavity may be returned to the oil inlet to refill the undervane spaces. It is also known to use anti-slugging valves to clear oil from the compression cavity.
An example of such means is found in U. S. Patent 3,385,513, issued May 28, 1968.

In the present invention, a substantially incompressible fluid, such as lubricating oil, is caused to flow into the undervane space defined by the bottom of the vane pocket, the underside of the individual vane, and the end plates on opposite sides of the ro-tor. The impor-tant distinc-tion between the present invention and known prior : 07~0~S-~-Y
., , , . ;
,` :` 1~54~4 . . t :t compressoxs op~rating on similar pri.nciples is tha~ th~

qu~ntity o~ fluid injected under the vane is relatively i , . ~ .
fixcd. Thi5 is accomplished by trappin~ a volume o~ fluid underneath the vanes at a predetermined point upstream from .`
the contact point. The trapped fluid is then squeezed out '~ through the running clearances between the side.. faces o the i~ rotor and the end plates as the vane contracts to its fully ., , .~.
. collapsed position adjacent the contact point. The rotor ; then rotates beyond the contact. point with the vanes moving :: :
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,., outwardly with substantially no fluid underneath the vanes . `::
.. ... . . .
~: until it reaches some predetermined point beyond that in . .. -~ :

`~ which suction is closed but spaced from the contact point .which constitutes the end of the compression zone.

~: ~ The amount of fluid available for delivery to the ~: :

~: undervane spaces is critical; If it is too little, the ..

spaces will be "starved"; and if too much, excess Iubricating !~
'j, : , ~ '.'':. :
oil will be delivered into the compression chamber via the ; olearances on the rotor faces etc. Accordingly, a meterlng : device is provided~whioh periodlcally interrupts~the~flow of 1 oil ana is proportional to compressor rotor speed. Thus a predetermined-"shot" of oil;is passed along to the undervane space in just the~amount and at the time needed for optimum .. ..

.performance.
I The metering devices also performs another important .~ .
i~ function as will be described now. In the typloa1 refri~
geration system, refrigerant vapor is delivered from an evaporator to a compressor whioh compresses the vapor for delivery to a condenser. Accordingly, the inlet to the ~ , ...
;~ compressor :is at a relatively low pressure and the discharge l outlet from the compressor is at a~relatively high pressure. .` ::

Most rotary vane compressors employ a differenti.al "~. .

: : oilin~ or lubrication system. More particularly, the oil ..

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s p is. located on the discharge sid~ of the compressor so that~ the oil pressure is essentially equal to the compressor discharge pressure. The oil sump is connecte~ by an oil -passage to the interior of the compressor and empties into the compressor at some point which is lower in the pressure than the oil pressure.
In the present invention, where a predetermined quantity of oil is trapped in an undervane space as it moves from the point where suction is closed to the discharge valve. When the compress~r is turned off, the pressure of ~¦
the incoming oil (which remains at substantially discharge '-pressure until enough time has elapsed to equallze the pressure through the system) would tend to force the vane -outwardly within its vane pocket against the cylinder wall. -~
In this case, the vane tip wants to follow the path of least resistance to relieve the,pressure being applied underneath `' and in so doing tends to follow the cylinder wall backwardly ' where the diameter is larger. This causes reverse rotation of the rotor which may cause the fluid to flow to the evaporator and superheat the gas in cycling clutch operations. It is also very annoying to the operator to have the compressor running (backwards) after it has been turned off.
In the present invention the oil flowing to the undervane spaces from the sump passes through a series of oil passages in the housing and in the discharge gas chambèr.
At one point, an interrupter of the metering device previously described is provided so that the flow'of oil is periodically interrupted enroute to the rotor. When reverse rotation begins to occur, the rotor will move back, but only to the ' point where oil flow is interrupted and thus will cause the 07~10~ Y

lOS41~4 rotor to cease further movement because the oil pr~ssure i5 discontinued at this point.
In a preferred er~odimcnt, the interrupter is in the form of a disc having a series of spaced openings which intermittently register with the stationary terminus of the oil passage through one of the side plates and an oil feed tube leading from the sump. Thus the flow is blocked by the web portion between the openings for a period of time until an opening in the disc registers with the oil feed tube outlet and permits the oil to flow through to the inlet of an oil passage leading to the undervane spaces.
Still another aspect of the present invention is directed to rather sp$cific problems which are present in most rotary sliding vane compressors. When the compressor is energized after standing idle for a period of time, there is a tendency for the vanes to stick to their most retracted position. When the rotor assembly is at rest, it will be apparent that the vanes will be in varying degress of extension, depending on their position relative to the point of tangency (contact) between the rotor and the cylinder wall. A vane at the contact point will be fully retracted and a vane directly opposite the contact point may be fully extended.
All others will be at some intermediate length of extension.
As the rotor moves past the contact point, the vanes are -pushed to their most radially inward position. At startup, the rotational veloc ty is not sufficient to produce enough centrifugal force on the vanes to keep the tips in engagemer1t with the cylinder wall. Moreover, a vacuum is created in the undervane space as the vanes began to move out~Jardly. ~ -This is analogous to withdrawing a cork from a bottle rapidly, 07~0~ Y
105~

thus creating a vacuum within the bottle which opposes the effort to move it out. This problem is compounded by the stic~y condition of the lubricating oil in and around the vanes which has an additional retarding force on vane movement.
Another problem is caused by the fact that the lubricating oil is at least partially miscible with the re~rigerant. During normal operation, most of the oil is -removed from the d1scharge gas and collected in a sump.
From there, it is transferred to critical moving parts for sealing and anti-friction use. The remaining portion is circulated through the system with the refrigerant.
When the compressor is shut down, a considerable amount of oil tends to migrate back to the compressor and condenser and floods the compression cavity and rotor. Some oil finds its way under the vanes, that is the space defined between the faces of the vane slot, the bottom of the vane slot, the lower edge of the vane and the two end plates.
When the compressor is started up, the oil, being essentially noncompressible, offers resistance to the movement of the vanes inwardly and creates great pressure at the vane tip/cylinder wall interface. The only place for the oil to flow as the vanes collapse is through the clearances; and in the conventional compressor, the oil cannot flow fast enough to prevent the pressure from building up.
In order to overcome the foregoing problems, the present invention proposes that the undervane spaces be relieved to a high pressure zone as they pass into the initial phase of the suction cycle. In this way, the vacuum which would otherwise be created is relieved instantaneously, lOS~
thus allowing the vanes eo move freely outwardly against the ~ylinder wall. Once the rotational speed is up to normal, the centrifugal force is sufficient to overcome any tendency to stick; so that the vacuum relief does not play a significant factor in the operation of the compressor after it attains normal speed. In addition, an extension of the vacuum relief slot -communicates with the undervane spaces in such a way that it ~-cannot interconnect with the oil supply port. During the phase that the vane collapses, the undervane liquia is pumped back to the suction cavity through the vacuum relief slot.
In summary of the above, therefore, the present invention may be defined as providing a rotary sliding vane compressor comprising: a housing providing a gas working chamber having a cylindrical wall and including end plates closing the chamber; a cylindrical rotor mounted for rotation in the chamber and having opposed end surfaces~ and a plurality of inwardly extending vane slots formed in the rotor; the rotor being in sliding contact with the cylinder wall at a contact linej a gas ` `
inlet port communicating with the chamber; a gas discharge port adjacent the contact line communicating with the ~hamber; a gas discharge chamber associated with the housing, the gas discharge chamber having a sump portion for the accumulation of lubricating fluid separated from the gas; a plurality of vanes slidable in the vane slots, each vane having one end the~eof flush with one of the end surfaces of the rator, a vane tip in contact with the cylindrical wall and a lower edge defining, in cooperation with - the bottom of the vane slots and at least one of the end plates, an undervane space; means defining a first fluid passage in the -one end plate having a fluid supply port at one end of the passage and an inlet at the opposite end, the supply port being located so that it communicates with an undervane space as the rotor moves in a direction from the gas inlet port to the gas discharge port, the fluid su ~ y port being out of communication .B - 9 -- 1054~14 with the undervane space before the vane tip reaches the contact . line, means for supplying a substantially incompressible fluid : to the inlet whereby the fluid flows through the passage and . . fills the undervane spaces, trapping a predetermined quantity of fluid in the undervane spaces, the fluid being confined, except for high flow resistance leakage paths between the rotor and the housing, and between the vanes and the vane slots, as the vane approaches the contact line, the last-named means including a conduit through which the fluid is transferred from the sump portion under pressure of discharge gas in the sump portion, having an outlet aligned with7 but spaced from, the fluid supply passage inlet and a disc-like element interposed between the conduit outlet and the fluid supply passage inlet and driven with the rotor, the element having a plurality of apeTtures . therein adapted to intermittently and periodically interconnect the conduit to the fluid supply passage and means defining a second fluid passage in one of the end plates, the passage having a first portion adapted to communicate with the undervane spaces, the second fluid passage having a portion which extends into the gas working cha~ber so as to relieve suction crea,ed by the vanes moving outwardly during the suction phase. ~.
In the accompanying drawings:
PIGURE 1 is a cross sectional view of a rotary com-pressor constructed in accordance with the principles of thepresent invention;
FIGURE 2 is a cross sectional vie~ taken along the plane of line 2-2 of PIGURE 1;
FIGURES 3-6, inclusive, are each a detailed view showing the lower portion of the vane pocket at various positions between full extension of the vane and the completely collapsed position thereof;
FIGURE 7 is a cross sectional view taken along the plane of line 7-7 of FIGURE 1~ illustrating the interrupter .~ - 9a -lQ541~
-~ element in position relative to the oil flow passage; and FIGURE 8 is a plan view of the rear end plate.
Referring now to the drawing, particularly to FIGURE 1, there is shown a rotary compressor of generally conventional ~-~
design including a stator housing 10 comprising a cylinder bloc~
12 having a circular bore extending therethrough to provide a cylinder wall 14, a front end plate 16, - - 9b -' .

. .. .: ~

1054~
and a rear end plate 18. Within housing lO there is provided a rotor 20 connected to and driven by drive shaft 22. The rotor 'is eccentrically mounted within the cylinder 14 so that it is in close running contact with the cylinder wall 14 along a contact line 24 and forms a cresent-shaped gas working space or compression cavity 26. The rotor is provided with a plurality of vane slots 30 each having a bottom surface 32 and receiving vanes 34 which are adapted to reciprocate within each va~e slot with their upper edges 34a in continuous engagement with cylinder wall 14. It may be seen that the lower sides of each ~ ;
slot, the bottom edge 34b of the vanes 34, and the bottom of the vane slot 32 define what will be referred to as the '~undervane - space", designated 35.
Suction gas is admitted to the compression cavity 26 through connection 36 and passage 38. Gas is discharged through a series of openings 42 (adjacent the contact line), covered by reed-type discharge valves 44, into discharge gas plenum 50, and :
then flows into passage 52 in rear plate 18 and out through connection 54. ~ . A housing 56 is secured to the rear plate 18 and provides a discharge gas chamber 57 having a lower sump portion 58 for the collection of lubricating oil which is separated from the discharge gas as it passes through separator 60 in - route to the discharge gas connection 54. An oil pickup tube 62 . extends downwardly into the sump and communicates with an oil feed passage 66 extending through the rear bearing plate 18 and opening up into a kidney shaped port 68 located at a point which intercepts the undervane spaces 35 as the rotor approaches the contact line 24.
As the oil flows through the oil pickup tube it passes through a rotating interrupter device ~4. This dap/

O / ~10 '~ - Y
1(:)59~4 device will be described .in more detail below.
The port 68 is located, shaped and dimensioned so that, under a wide range of operating condi.tions, a pre-determined quantity of lubricatin~ oil will be fed (by the pressure of discharge gas acting on the surface of oil 70 in s~p 58) into the spaces 35 underneath each vane. As the ~ rotor travels beyond the far end of ~ort 68, the oil will be -~
. ~ trapped within the undervane space ~ . .
The boundaries of undervane spaces 35 are provided by the lower edge 34b of vanes 34, the bottom portion 32 of .
vane slots 30 and the front and rear plates 16, 18. The 4''~ n7a.Q~V only escape routes for oil trapped in the undervane - :
spaces are the clearances between the front and rear surfaces of the vanes and the vane slots and the clearances between - .
the end surfaces 20a, 20b of rotor 20 and the front and rear pl~tes 16, 18. These clearanccs, of course, are small and ~:
they pose high resistance flow paths for the oil as it.is forced out of the undervane space by the collapsing vane approaching the contact point. This resistance maintains : -pressure on the vane to keep the vane tip 34a in firm engage-ment with the cylinder 14.
As best shown in FIGU~ES 2 and 8, there is a ~
shallow channel or slot 80 formed in the surface of rear - . ~.
plate 18 (or optionally in front plate 16). Slot 80 has a radially extending portion 92 to relieve vacuum i.n the undervane spaces to make sure that the vanes are properly - --extended under startup conditions. Associated with slot 80 is a passa~e 90 which is formed in the rear bearing plate 18 (or optionally in front plate 16j. Passage 90 is mille~ in :

the form of an arcuate ~roove communicating with the suction .. . .

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side vacuum relief slot 92. The purpose of this passage is to selieve the liquid which may be present in the undervane space 35 at startup conditions and the details are more fully described ~ -below.
A more complete understanding of how the undervane spaces are filled, and how the oil is trapped, ~ay be ga~ned by reference to FIGURES 3 to 6 which show the relationship of the spaces to the port 68. In PIGURE 3, the undervane space 35, moving in the direction of the arrow, is just approaching the port 68. In contrast with prior art arrangements, the spaces are substantially free of oil or other fluid at this point, because it ls not necessary indeed undesirable - to force the vanes outwardly during the phase of rotation through the suction zone.
In FIGURE 4, the space 35 has ~ust passed into fluid communica-- tion with port 68 thereby admitting oil to the space and filling it completely. In FIGURE 5, the undervane space is approaching the far end of port 68 and is about to trap whatever oil remains - in the space, it being understood that the volume of the space is contracting slightly as the space passes from one end of port 68 to the other. In FIGURE 6, the vane space 35 has passed beyond the far end of port 68 so that since a predetermined amount of oil is now trapped between the end of port 68 and the contact line 24, some oil will be squeezed out through the clearances between the rotor end faces 20a and 20b and plates 16, 18 and also between the faces of the vanes and the surfaces of the vane slots.
As mentioned above, the oil enroute to the cavity 68 from the sump 58 passes through an interrupter device 64 dap/

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which is mounted for rotation on the rear of drive shaft 22 between the discharge gas chamber 57 and the back side of rear end plate 18. The device 64 (see FIGUR~S 1 and 7) comprises a disc 63 having a plurality of spaced apertures ~5, each of which are substantially larger in diameter than the diameters of oil passage 66 and oil pick-up tube 62.
Disc 63 is held between a boss 67 on the rear plate 18 and a retaining plate 69 through which the end of -oil pick-up tube 62 extends. During operation, the disc 63 will rotate with rotor 20 causing apertures 65 to inter-mittently register with the entrance end 66a of oil passage 66 and the discharge end 62a of oil pick-up tube 62. During this interval, oil will flow through the passage 66 to cavity 68. ~hen the web portion 63a of disc 63 passes between 66a and 63a flow will be interrup~ed.
The cooperation between the interrupter ~nd ~he undervane liquid feed is quite important to the successful operation of the compressor. Since the disc 63 is driven with the rotor the amount of oil available to be fed to cavity 68 is directly proportional to the requirements.
Each time one of the apertures is in registration with the end of pick-up tube 62 and passage 66, a predetermined quantity of oil passes through and is made available for undervane feed. ~s the speed of the rotor increases, the oil flow is increased proportionally.
The other function of the interrupter may be explained as follows: When the compressor is shut down, the rotor (and disc 63) may come to rest at a position in which one of the apertures 65 permits oil flow. In such case, the pressure will be ap~lied to ~he underside of vane 3~a (at ` 07~0~8-~-Y

~05~
cavity 68). The force transmitted through the vane, at the ; tip, will cause the vane to cam backwardly along the cylinder wall 14 in an effort to seek a larger diameter position.
However, as soon as it moves to a point where a web portion 63a of disc 63 cuts off flow, then the pressure under vane 34a will stabilize, and rotation will cease.
As best shown in FIGURES 1, 2 and 8, there is a shallow generally L-shaped slot 80 formed in the surface of rear plate 18. In accordance with this invention, one purpose of this slot is to relieve vacuum in the undervane space to make sure that the vanes are properly extended under startup conditions.
Slot 80 has an elongated arcuate section 90 which is spaced from the axis of rotation by a distance approxi-mately equal to the distance between the rotational axis and the bottom of the vane slots. A second section 92 extends generally radially from one end of section 90, and, at best illustrated in FIGURE 2, has its terminus 93 extending beyond the edge of the rotor into the suction zone of com- ~-pression cavity 26. The other terminus of the slot, desig-nated at 94, extends ~ust beyond the section line 1-1 as shown in FIGURE 2. This permits any liquid under the vane, which may be present at startup conditions, to flow into -`
passages 90, and 90 and 92 to be discharged into the suction zone of cavity 26.
It will be noted that the undervane spaces 35 are in communication with arcuate section 9~ for about 60 of rotation in the suction zone. Since section 90 communicates with section 92, the vacuum is immediately relieved under the vancs as they begin to extend. This allows free exten-sion of the vanes to engage the cylinder wal~ during startup so the compressor will not "stall"~

, ~ "

Claims (2)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
ROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A rotary sliding vane compressor comprising; a housing providing a gas working chamber having a cylindrical wall and including end plates closing said chamber; a cylindrical rotor mounted for rotation in said chamber and having opposed end surfaces, and a plurality of inwardly extending vane slots formed in said rotor; said rotor being in sliding contact with said cylinder wall at a contact line; a gas inlet port communicat-ing with said chamber; a gas discharge port adjacent said contact line communicating with said chamber; a gas discharge chamber associated with said housing, said gas discharge chamber having a sump portion for the accumulation of lubricating fluid separated from said gas; a plurality of vanes slidable in said vane slots, each vane having one end thereof flush with one of the end surfaces of said rotor, a vane tip in contact with said cylindrical wall and a lower edge defining, in cooperation with the bottom of said vane slots and at least one of said end plates, an undervane space; means defining a first fluid passage in said one end plate having a fluid supply port at one end of said passage and an inlet at the opposite end, said supply port being located so that it communicates with an undervane space as the rotor moves in a direction from said gas inlet port to said gas discharge port, said fluid supply port being out of communication with said undervane space before said vane tip reaches said contact line, means for supplying a substantially incompressible fluid to said inlet whereby said fluid flows through said passage and fills said undervane spaces, trapping a predetermined quantity of fluid in said undervane spaces; said fluid being confined, except for high flow resistance leakage paths between said rotor and said housing, and between said vanes and said vane slots, as said vane approaches said contact line, said last-named means including a conduit through which said fluid is transferred from said sump portion under pressure of discharge gas in said sump portion, having an outlet aligned with, but spaced from, said fluid supply passage inlet and a disc-like element interposed between said conduit outlet and said fluid supply passage inlet and driven with said rotor, said element having a plurality of apertures therein adapted to intermittently and periodically interconnect said conduit to said fluid supply passage and means defining a second fluid passage in one of said end plates, said passage having a first portion adapted to communicate with said undervane spaces, said second fluid passage having a portion which extends into said gas working chamber so as to relieve suction created by the vanes moving outwardly during the suction phase.

2. Apparatus as defined in claim 1 wherein said second fluid passage also includes a forwardly (in the direction of vane rotation) extending section adapted to relieve any lubricat-ing fluid accumulated under said vanes and permit it to drain to the suction side of said gas working chamber.