US1994786A - Compressor and vacuum pump - Google Patents

Description

March 19, 1935. s, B. REDFIELDA COMPRESSOR AND VACUUM BUMP Filed Feb. 14, 1954 INVENTOR 5i @IDF/'20 BY .7

um dgl/1s LA@ WM? ATTORNEYS Patented Mar. E9, E93

COMPRESSOR AND VACUUM PUMP Snowden B. Redfield, to Fuller Company,

Bethlehem, Pa., assignor a corporation of Delaware Application February 14, 1934, Serial No. 711,138

6 Claims.

This invention relates to rotary compressors and vacuum pumps, and more particularly to an apparatus for reducing the loss in eilciency due to air or gas leakage through the space between the rotating elements and the casing or cylinder heads.

The invention may be applied advantageously to rotary compressors and pumps having rotary elements of various types, to maintain a constant minimum clearance between the ends of one or more rotating elements and the inner surface of the cylinder or casing heads. Because of the wide variation in temperatures of the working parts and the relatively high rotor speeds, the invention is of greatest utility in its application to high pressure, multiple vane compressors and vacuum pumps and will accordingly be specifically described in its application to this type. As the relation of the parts of the present invention is the same in both compressors and vacuum pumps, the apparatus will be referred to hereinafter as a compressor.

In common commercial types of multi-vane compressors, such as that disclosed in Pfeiier Patent 1,890,003, the apparatus -comprises one or more stages or cylinders having oppositely arranged intake and discharge ports. The rotor is arranged eccentrically within the. cylinder with trunnion shafts carried in bearings in the cylinder heads. Vanes or blades moving in slots in the rotor divide the crescent-shaped space between it and the inner surface of the cylinder into a plurality of cells which progressively decrease in volume as they are rotated from the intake to the discharge side.

As the rotorsare normally driven by directly connected motors at speeds ranging from 1750 R. P. M. for the small sizes to 575 R. P. M. for machines having capacities of 1000 or more cubic feet per minute, actual free air delivery, it will be apparent that contact between the rotor and a cylinder head will .immediately cause the parts to burn and become welded, and that likewise suicient clearance must be provided to prevent the vanes from coming into contact with both cylinder heads at the same time.

In order to preventthis damage to the working parts, it has been the practice heretofore to x one of the trunnion shafts in its bearing assembly so that there will be no axial movement and to provide a xed clearance between the end of the rotor and the inner surface of the corresponding cylinder head, this clearance being the minimum safe running clearance, depending particularly upon the axial play of the (Cl. 23o- 152) bearingor bearings. Thus, this clearance may be, for the average size machine, .004 of an inch, which is slightly in excess of the normal play or axial movement of common types of roller and ball bearings. This clearance accordingly remains approximately constant, regardless of pressure or operating temperature. At the opposite or the expansion end of the cylinder, sufcient clearance must be provided to prevent Contact due to the expansion of the rotor and vanes at the highest operating temperature. The expansion of the rotor is relatively much greater than that of the cylinder, as only the latter is either water or air cooled.

Theoretically, it would be possible to adjust the clearance at the expansion end so that at the temperature corresponding to the pressure for which the apparatus was designed, the clearance after the rotor expanded would be equivalent to that of the fixed end. However, if the operator should nd it desirable to increase the discharge pressure, the consequent relative in. crease in temperature would result in additional expansion of the rotor, which would score the cylinder head and possibly weld the parts. Likewise in determining the clearance, provision must be made for increased relative expansion of the rotor with respect to the cylinder due to a decrease in the temperature of the cooling media below normal. y

As the cylinder is usually provided with water jackets, the expansion end clearance must be sufficient to provide for a running clearance under any condition of operation, the clearance necessarily being the sum of a running clearance in excess of the axial play of the bearings and a clearance to compensate for the elect of temperature at the highest operating pressure. As this clearance is excessive for all normal operation, the general eiilciency is considerably reduced by air leakage through this space and the eiciency is further impaired by expansion of the air on the intake side, resulting from the higher intake temperature. This also results in higher discharge temperatures, unsuitable for many purposes, as for instance in making the separation of oil and moisture from the air difcult.

In general, the new apparatus preferably comprises a. fixed cylinder head or end in which one trunnion shaft of the rotor is prevented from axial movement, and at which the distance between the end of the rotor and the corresponding face of the cylinder head may be established at the minimum safe running clearance. The opposite or expansion end, however, is provided l with a fixed head, which carries an internal head,

hereinafter referred to as the floating head, axially movable as the rotor expands or contracts, and which may be adjusted or fixed to maintain a desired running clearance, the clearance remaining approzn'mately constant regardless of temperature and being, if desired, equivalent to the clearance at the fixed end. In the preferred form of the invention, the xed head is provided with a, smooth bore of large diameter, concentric with the trunnion shaft, and which accommodates a hollow sleeve, preferably formed Vas an integral part of the floating cylinder head, the sleeve being arranged eccentrically at the rear of the fixed head, because of the eccentric arrangement of the rotor within the cylinder. The floating head jis preferably accommodated within a bore of slightly greater diameter than the cylinder, and cut into it for a distance greater than the thickness of the head, to permit the axial movement of the floating head. The space between the periphery of the head and the bore of the cylinder is sealed by suitable packing, preferably one or more rings, piston rings for large internal combustion engines being suitable for the purpose.

Within the sleeve the shaft is carried by a radial bearing, the outer race of which is spaced from the inner surface on the oating head by one or more shims, the thickness of which establishes the clearance between the inner face of the head and the rotor. The thrust due to expansion reacts against a thrust bearing, the assembly being securedto the sleeve so that expansion or contraction of the rotor will cause the sleeve to move axially within the bore of the i'lxed head.

As the sleeve is eccentric with respect to the floating head, partial rotation of the latter would cause it to jam or lock against axial movement in the bore within which it is accommodated. Accordingly, a dowel, flxed preferably in the floating head, and extending into a bore in the xed head, serves as a convenient device to locate the floating head.

It will be seen, as the description proceeds, that floating heads may be used at each end of the rotor whereby the rotor and heads may oat axially in either direction until contact is made with one fixed head. This duplication does not 'materially increase the operating advantages,

and as it is more costly than the arrangement described, the latter is preferred.

For a better understanding of the invention, reference is made to the drawing, in which Fig. 1 is a, cross-sectional elevation of the compressor;

Fig. 2 is a cross section.

Referring to the drawing the apparatus will be seen to consist of a cylinder l, having an intake port 2, a discharge port 3, and provided with a substantially cylindrical bore 4, excepting a counter-bored surface 5 at the bottom and between the intake and discharge ports. This counter-bore is concentric to a cylindrical rotor 6, arranged eccentrically within the bore 4 and which is provided with slots in which vanes or blades 7 are arranged to move outwardly and into contact with the inner wall of the cylinder, due to the effect of centrifugal force.

The blades 7 in their outward position divide the crescent-shaped space between the surface of the rotor and the inner Wall of the cylinder into a plurality of cells, which progressively decrease in volume toward the discharge side.

The rotor 6 is carried by trunnion shafts 8 and 9 in bearings, to be described more in detail hereinafter, in the cylinder heads 10 and 11. The cylinder is provided with suitable'water jackets 12, which communicate as at 13 and 14 with jackets in the heads 10 and 11, and it will be evident that these provide for adequate cooling of the stationary parts.

The fixed end of the rotor is carried by the head ll. The head 11 comprises an inner face 15 and is provided with a bore 16, through which the shaft 9 extends. 'Ihe head is bored to receive the outer race 17 of a roller bearing, which carries the radial load, the axial position of the race 17 and consequently the bearing being adjustable by lmeans of one or more shims 18, the shims 18 serving to establish the desired running clearance between the end of the rotor and the inner face 15 of the head 11. One or more perforated gaskets 19 seal the cylinder and head against leakage of air and cooling water.

A retaining ring 20 and a iixed ring 21 prevent axial movement of the radial bearing and abut respectively the inner and outer races of thrust bearing 22, the latter being retained on the shaft by lock-nut 23 and lock-washer 24. 'I'he bearing cover 25 is provided with internal ngers 26, which bear against the outer race of thrust bearing 22, and prevent outward axial movement of the rotor and bearing assembly. Lubricating oil entering through the duct 27 is allowed to circulate freely into both bearings, dueto the space between the rotating retaining ring 20 andthe flxed ring 21, and through the spaces between the fingers 26, which retain the outer race of the thrust bearing 22. The oil is prevented from escaping through the shaft opening in the bearing cover 25 by a suitable packing gland 28.

It will thus be seen that the fixed end of the rotor can be adjusted by means of the shims 18, for the desired running clearance and that this may be maintained regardless of variations in running temperature.

The expansion end of the compressor comprises a fixed head 10, which is provided with a smooth bore of relatively large diameter, concentric to the trlmnion shaft 8. A sleeve 30, preferably formed as an integral part of the oating head 31, is arranged within the bore to move axially therein as the rotor expands or contracts, as will be explained more in detail hereinafter. The sleeve 30 is eccentric to the moving or oating head 31, as the latter preferably has the same center as the bore of the cylinder l. The oating head 31 is preferably accommodated within a relatively shallow, circular bore 32 of slightly greater diameter than the bore of cylinder 1, with a radius equall to or slightly greater than the distance between the center of the cylinder bore and the surface of the undercut section 5, in order to. seal the end of the cylinder.

It will be understood that in compressors having a true cylindrical bore, a bore of greater diameter, to accommodate the head 31, will not be necessary. Air leakage across the periphery of the head 3l is prevented by at least one and preferably two sealing rings 33, which are accommodated in slots cut into the periphery. The rings 33 may be of any suitable type of packing, but experience has shown that piston rings of the well-known snap type or of the type used in large internal combustion engines are most effective.

Lubricating oil is conveniently admitted after negarse the manner described in the Pfeiffer patent above mentioned, through a duct 34 which communicates with a groove cut between the sealing rings 33 and which communicates with a duct 35 which admits the oil to the interior of cylinder 1 near the base of the slots which accommodate the blades 7.

The trunnion shaft 8 passes through the opening 36 in the head 31 and is shouldered at 37 to form an abutment for the inner race of a radial roller bearing 38, the outer race of which bears against one or more shims 39, which space it from the inner wall of head 31. The bearing 38 carries the entire radial load of this end of the rotor, and it will be understood that this is relatively great in view of a large rotor area exposed on the pressure side of the machine. The thrust load, particularly that due to expansion and contraction of the rotor is carried preferably by the double row ball bearing 40, the inner race of which is separated from that of the radial bearing 38 by the rotating spacer ring 41 and the outer race of the ball bearing' by the stationary spacer ring 42, the latter being provided with bores as at 43 for the passage of lubricating oil. The bearing assembly is secured to the shaft by the lock nut 44 and lock washer 45, which bear against the inner race of bearing 40. The outer race is held in place by a bearing retainer 46.

The running clearance between the end of rotor 6 and the inner surface of vhead 31 may be adjusted to a minimum clearance, for example equivalent to the clearance at the flxed end of the cylinder, the degree of spacing being determined by the thickness and number of shims 39.

Sufcient clearance must be provided between the outer face of the head 31 and the inner face of the flxed head 10, to allow at least for the maximum expansion under any condition. The gasket or gaskets 47, like the gaskets 19 at the opposite end of the cylinder have no function other than to prevent escape of air and cooling water.

It will thus be seen that by the rigid assembly of the bearings on the trunnion shaft 8 and in the sleeve 30, expansion or contraction of the rotor will move the entire assembly in the bore of flxed head 10 and that the running clearance will remain substantially constant for all temperature conditions.

In order to establish a definite air or gas .pressure on the outer surface of head 31, the head is bored as at 48 for balancing purposes. 'I'he location of this bore is not arbitrary, and although it is shown in the preferred position, it may be located anywhere around the path of the vanes in the crescent shaped space. This vent opening allows air to pass through the floating head, but it does not permit through air leakage, as it connects with but one pressure zone and not from zone to zone or from discharge to intake, where leakage occurs in previous types of machines.

As the sleeve is eccentric to the floating head 31, the tendency to rotate is prevented by a dowel 49, secured to the head 31, and which projects into a hole 50 in the flxed head 10. In the absence of a dowel or equivalent device to prevent rotation, the head 31 would tend to rotate until it became tightly engaged with the walls of the bore 32, whereupon the contraction or expansion of the rotor might result in the destruction of the thrust bearing 40, and if the compressor continued to run, expansion would ultimately score the rotor and head 31 and possibly cause these parts to become welded.

I claim:

1. A-rotary compressor of the multi-vane type, comprising the combination of a stator casing having a substantially cylindrical bore provided with an air inlet and an outlet, a cylindrical rotor arranged within the bore having shafts mounted in bearings in fixed heads closing the ends of the casing, at least one of the heads being provided'with a bore concentric to the corresponding rotor shaft, the casing having a length greater than the rotor to provide a chamber between the end of the rotor and the flxed head, a floating head having a cylindrical portion arranged within the casing and a hollow sleeve concentric to the rotor shaft and arranged within the bore of the flxed head, a thrust bearing having an outer race secured to the sleefe and having an inner race secured to the shaft to cause the floating head to move therewith as the rotor expands or contracts, and means to x a clearance between the inner surface of the floating head and the end of the rotor.

2. A rotary compressor comprising the combination of a stator casing, having a central bore, and an air inlet and outlet communicating therewith, a rotor within the bore having shafts mounted in bearings in fixed heads closing each end of the bore, the casing having a length greater that the rotor, at least one floating head arranged within the casing having an inner surface adjacent and parallel to an end of the rotor, the floating head having a bearing chamber, a thrust bearing within the chamber having an inner race secured to the shaft and an outer race secured to a wall of the chamber, means surrounding the bearing and extending rearwardly from the floating head to guide the latter axially and prevent angular displacement, the flxed head being bored to receive said means.

3. A rotary compressor comprising the combination of a stator casing having a central bore and an air inlet and outlet communicating therewith, a rotor within the bore having shafts mounted in bearings in flxed heads closing each end of the bore, at least one of the heads being provided with a bore concentric to the corresponding rotor shaft, the casing having a length greater than the rotor to provide a chamber between the end of the rotor and the flxed head, a floating head having a cylindrical portion arranged within the casing and a hollow sleeve concentric to the rotor shaft, and arranged within the bore of said fixed head, a thrust bearing having an outer race secured to the sleeve and having an inner race secured to the shaft to cause the sleeve to move axially as the rotor expands or contracts to maintain a substantially fixed clearance between the inner surface of the floating head and the rotor.

4. A rotary compressor comprising the combination of a stator casing having a central bore and an air inlet and outlet communicating therewith, a rotor within the bore having shafts mounted in bearings in flxed heads closing each end of the bore, at least one of the heads being provided with a bore concentric to the corresponding rotor shaft, the casing having a length greater than the rotor to provide a chamber between the end of the rotor and the flxed head, a floating head having a cylindrical portion arranged within the casing with an inner surface adjacent and parallel to the end of the rotor and means responsive to thrust to cause the floating head to move axially as the rotor expands or contracts and to prevent angular displacementI of the oating head comprising a hollow sleeve extending rearwardly from the cylindrical portion and arranged within the bore of said xed head, a thrust bearing within the sleeve having an inner race secured to the rotor shaft and an outer race secured to the sleeve.

5. A rotary compressor comprising the combination of a stator casing having a central bore and an air inlet and outlet communicating therewith, a rotor within the bore having shafts mounted in bearings in fixed heads closing each end of the bore, at least one of the heads being provided with a bore concentric to the corresponding rotor shaft, the casing having a length greater than the rotor to provide a chamber between the end of the rotor and the xed head, a iioating head having an inner cylindrical portion arranged within the casing and a rearwardly extending hollow sleeve concentric to the rotor shaft, and arranged within the bore of said fixed head, and means responsive to thrust to cause the oating head to move axially as the rotor expands or contracts to maintain a substantially constant clearance between the inner surface of the oating head and the end of the rotor, comprising a bearing within the sleeve having an inner race secured to the shaft and an outer race secured to the sleeve.

6. A rotary compressor comprising the combination of a stator casing having a central bore and an air inlet and outlet communicating therewith, a rotor within the bore having shafts mounted in bearings in xed heads closing each end of the bore, at least one of the heads being provided with a bore concentric to the corresponding rotor shaft, the casing having a length greater than the rotor to provide a chamber between the end of the rotor and the fixed head, a floating head having an inner cylindrical portion arranged within the casing and a rearwardly extending hollow sleeve concentric to the rotor shaft, and arranged within the bore of said fixed head, a radial bearing within the sleeve having an inner race secured to the shaft adjacent to the end of the rotor and means responsive to thrust to cause the floating head to move axially as the rotor expands or contracts, comprising a thrust bearing within the sleeve having an inner race secured to the shaft beyond the radial bearing, and an outer race secured to the sleeve.

SNOWDEN B. REDFIELD.

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