US2015124A - Compressor and vacuum pump - Google Patents

Description

Sept. 24, 1935. Q PFElFFER I 2,015,124

COMPRESSOR AND VACUUM PUMP Filed March 1, 1934 Flag I IINVENTOR c5542 Pff/fffP ATTORNEYS" Patented Sept. 24, 1935 UNITED STATES PATENT -OFFICE 2,015,124 COMPRESSOR AND VACUUM PUMP Csar Pfeiffer, Asnieres, France, assignor to Fuller Company, Catasauqua, Pa., a corporation of Delaware Application March 1, 1934, Serial No. 713,468

In France March 16, 1933 3 Claims. (01. 230-453) which the vanes, carried by a cylindrical rotor,. pocket the air or other gas in a crescent-shaped 5 space between the inner wall of the stator casing and the surface of the rotor, arranged eccentrically within it. It is especially concerned with,

positive means for forcing the vanes outwardly, and maintaining them in contact with the cylindrical or substantially cylindrical bore of the casing.

For simplicity, the apparatus will be described hereinafter as an air compressor, but it will be understood that it can be employed to compress other gases and as a vacuum pump.

In my'Patent No. 1,890,003; of December 6, I932, I have illustrated and described a compressor or vacuum pump, in the operation of which centrifugal force alone is relied upon to cause the vanes to move outwardly from their innermost positions in the seal space between the dischargeand intake sides of the casing, to their outermost positions at the plane of greatest depth of the crescent-shaped space. Machines of this type have proven highly satisfactory for working pressures up to approximately 60 pounds gauge, and for corresponding compression ratios when employed as the second stage of a compound machine.- At speeds ranging from 1750 R. P. M.

for low capacity machines to 5'75 R. P. M. for the larger sizes, the centrifugal force factor is high enough to cause the vanes to remain in contact with the cylinder wall by overcoming the forces which tend to cause the vanes to react in the vicinity of the discharge port and forces which tend to retain them in their slots on the intake side. i

It is among the purposes of the present inven tion to extend the useful applications of com- 40 pressors of this type, particularly to permit increased discharge pressures with maintained efiiciencies. Likewise the improved apparatus can be employed without loss of efficiency under abnormal conditions of low temperature, which may be encountered in certain classes of service. If

likewise result in a further decrease in efliciency, due to increased discharge temperature. The

resulting increase in pressure differential in the cell or pocket immediately behind this vane imposes an excessive shearing stress on the vane 5 on'the opposite side of the cell.

It is undesirable to attempt higher pressures by increasing the centrifugal force factor either by increasing the weight of the vanes, the speed of rotation or both. For obvious reasons of me- 10 chanical efficiency, particularly with reference to friction loads and also to avoid excessive wear on both the vanes and cylinder wall, the vanes should be as thin or as light in weight as mini,- mum practical strengths will permit. It is de- 5' sirable to employ steel vanes of thicknesses normally ranging from .0391 to .059 of an inch and to provide rotor slots having clearances as low as .002 of an inch to reduce slippage of air around the vanes in their slots. 20

Accordingly, another factor that may cause the vanes to be retained in their slots, and particu-' larly after they pass the seal space between the discharge and intake ports, is the adhesion of the vanes to the walls .of the slots. the comparatively large surface area of the vanes within the slots in these locations, it will be seen that when starting under abnormally low temperatures, the oil viscosity may be such that centrifugal force is insufiicient to move the vane 30 uniformly'outward to make contact with the'cylinder wall. This condition is aggravated if dirt, carbon deposits or other oil residues are present in the slots. Although this latter difiiculty can be overcome by careful operation, particularly by 35 employing cleansing agents or light lubricants when starting the machine, it is obviously preferable to provide positive means to maintain the contact desired at all times. Although it is the primary purpose to extend the utility of the apparatus to higher working pressures than those for which it is normally employed, it is also a purpose of the invention to permit the use of oils which retain their lubricating qualities at temperatures corresponding to the operating 45 pressures rather than to sacrifice these qualities to avoid eificiency loss due to heavy oil viscosities when starting cold machines and to obtain these advantages without material loss in air slippage from the high to the low pressure side of the 60 cylinder.

In general, the new "apparatus comprises a machine of the type described, in which the rotor is bored diametrically to accommodate pins or pushrods. At least two push-rods, equidistant from Thus, in view of 25 v the opposite ends of the rotor, are provided for each pair of oppositely arranged vanes. The opposite ends of the rods abut the bases of the vanes, as will appear more fully hereinafter.

In the preferred embodiment of the invention, the bores are not drilled entirely through the rotor, but only far enough to insure the maximum outward movement of the vanes, in order to avoid leakage of air through these openings. The clearance between the push-rods and the wall of the bore is preferably limited for the same reason to a running fit at the operating temperature. These rods are preferably simple cylinders with fiat ends, and of a thickness considerably greater than that of the vanes, to insure engagement and to prevent angular movement of the latter, especially due to the mechanical difficulty of drilling the rotor on true diameters, exactly centered with the slots.

The minimum distance across the cylinder and through the center of the rotor is on the diameter of the latter where the vanes are equidistant from the center. Accordingly, I prefer to make the push-rods of such length that, at the temperature corresponding to the highest working pressure, the rods and vanes will be in contact and the latter in contact with the cylinder wall with no more clearance than a running fit at the point where the vanes coincide with the line of minimum distance aforesaid. The maximum distance is a line passing through the center of the rotor which intersects the line described above at an angle of 90 degrees.

The difference in length of these lines is equal to the distance between the longitudinal center lines of the cylinder and rotor; i. e., the eccentricity less the sum of the distances between the cylinder and rotor on both sides of the latter on the first-mentioned diameter.

It obviously follows that when the vanes reach the plane of the longest distance, there will be a gap between the vanes and the push-rods, which will be at a maximum in this plane, and that the length of the gap increases progressively from the plane of the shortest distance. It is common practice in compressors of this type to under-cut the cylinder wall between the intake and discharge ports, to form a seal space. The curve of this surface is concentric to the rotor, and this further displacement of the latter obviously contributes to the length of the gap referred to above. It is obviously of advantage, accordingly, to limit the depth of the seal space beyond the cylinder proper to the minimum which will seal the machine effectively.

The maximum gap occurs between the base of the inner vane and the push-rod, since the latter is off center and centrifugal force causes it to abut the outer vane. The outer vane maintains its contact with the cylinder wall because it has reached the.location where centrifugal force is greatest, and where back-pressure against its edge is at a minimum. At all intermediate planes, the gap is not sufficient to result in material air slippage losses, due either to back-pressure on the edges of the vanes, or to the forces tending to hold the vanes in the slots.

Although the invention finds its greatest utility when employed with relatively thin steel vanes and in machines operating under the high pressure conditions described above, it will be apparent that it may be used with vanes of other composition, such as those made of phenol condensation product, such as the material commonly known by the trade name Bakelite. The lighter weight, greater thickness and consequently greater edge area subjected to back-pressure has heretofore restricted the economical use of this material to considerably lower operating pressures than 5 can be obtained with steel vanes. Such vanes do not wear the cylinder wall, but they have the disadvantage of loss in efficiency even at comparatively low operating pressures, due to reaction on the discharge side and consequent air slippage or 10 blow-back past the edge of the vane and into the pocket or cell on the side nearer the intake. The use of push-rods, accordingly makes it possible to employ these materials and obtain high efficiencies with no damage to the cylinder walls. 15

I am aware that it has been proposed heretofore to provide rods connecting oppositely arranged blades or pistons, the rods being secured to at least one blade. These arrangements are adaptable only to relatively low-pressure blowers, 20 and particularly where high operating efficiencies are not demanded. They are not suited to thin vanes, as these must be free to avoid air slippage or blow-back, to obtain high efficiencies and to operate at high pressures. Likewise, machines of 25 the type contemplated herein are operated at speeds too great to permit rigid construction.

For a better understanding of the invention, reference is made to the accompanying drawing, in which 30 Fig. 1 is a typical cross-sectional elevation of the compressor,

Fig. 2 is a detail side elevation of the rotor, and

Fig. 3 is an end view of the-rotor.

Referring to the drawing, and first to Fig. 1, 35 the apparatus will be seen to consist of a stator casing I, having a cylindrical bore 2, and which may have an under-cut surface 3, extending beyond the radius of the cylinder to form a seal space. The under-cut surface is concentric to 40 the rotor 4, and spaced therefrom a distance of a running fit at the temperature corresponding to the maximum working pressure. For convenience, the bore of the stator will hereinafter be referred to as the cylinder. An intake port 5 4 3 and discharge port 6 communicate with the cylinder and the latter may be bored as at I at various levels to permit the discharge of air to avoid increases in pressure within the machine beyond the maximum for which it is intended. 5i)

The rotor 4 carries pairs of oppositely arranged vanes 8 and 9, which slide in radially cut slots l 0. Three pairs of vanes are shown for convenience, but it is to be understood that any number may be provided, the number of vanes employed depending upon the working pressure at which the machine is intended to operate. Greater numbers are used as the pressures increase, in order to reduce the pressure differential between the pockets into which the crescent-shaped space be- 60 tween the rotor and the cylinder wall is divided by the vanes. This obviously permits the use of vanes of minimum thickness, as limited by minimum strengths and centrifugal force factors.

As will be seen more clearly in Figs. 2 and 3, 5 the rotor is bored diametrically, as at H and I2, the centers of the bores corresponding to the centers of the vane slots 13. To avoid confusion, the depth of the slots is not indicated by dotted lines, but may be projected from Fig. 3. The 70 slots are preferably out after the rotor is drilled, to avoid curvature.

To avoid excessive air leakage through the openings thus provided, the bores are not drilled completely through the rotor. but only for a suf- 2,010,124 iicient depth to accommodate the push-rods u and to cause the latter to contact the bases of the vanes when they lie in a horizontal plane passing through the center of the rotor. This is the shortest distance across the cylinder 2 of the center of the rotor. The push-rods are, accordingly, of a length, corrected for temperature, suflicient to force the vanes to their extreme outward positions in this plane, and are of a thickness considerably greater than the vanes,

in order to insure continuous contact.

= cylinder 2 are on the same vertical centerline.

The distance across the cylinder is greatest in this vertical plane,and accordingly a gap is formed at It between the base of the inner-most vane and the bottom of the push-rod. The length of the gap increases progressively from, a minimum in thev horizontal to a maximum in the vertical plane. The length of the gap varies with the decree of eccentricity of the rotor and cylinder, and equals the difference between the width of the vertical and horizontal planes referred to above, plus the depth of the under-cut surface or seal space.

Referring again to Fig. 1, it will be evident that where the gap is j'longest, theoutermost vane is 'in a position where centrifugal force is greatest, and as it is at or just beyond the intake, little or no reaction due to pressure is exerted at its outer edge, and as a minimum of its surface area is within the slot and subject to the retarding effect of the lubricating oil or foreign material, the contact made when it was in the horizontalposition is maintained.

The operation of the apparatus will be obvious from the foregoing description, and it will be realized that unlike the present arrangement the vanes will remain in their outward position even when the machine is idle. It will be seen that as the vanes leave the seal space, the inward movement of the opposite vanes on the pressure side will force them outwardly and overcome the effect of viscosity and foreign matter. Likewise reaction of the vanes on the pressure side, due to.

pressure on their edges, is restrained by the opposed vanes. The large diameter of the'pushcommunicating with said slots, and having a diameter greater than the width of the slots a depth less than the diameter of the rotor to prevent excessive leakage through thebores, opposite pairs being drilled from opposite sides of the .5

rotor and spaced equidistantly from the ends thereof, solid, cylindrical push-rods of greater thickness than the vanes movable in the bores, and abutting the faces of the vanes to cause each inwardly moving vaneto push its opposite out- 10 wardly to overcome forces tending to retain the latter in its slot, the push-rodslikewise preventing material loss of contact of the inwardly moving vanes with the cylinder, due to the effect of I pressure on thesurface of its outer edge. 15 2. A rotary compressor of the multi-vane type,

comprising the combination of a cylinder having intake and discharge ports communicating therewith substantially on opposite sides, a rotor arranged. eccentrically'therein to provide a cres- 23 I cent-shaped space between its surfaceand the wall of the cylinder,,the rotor being provided with narrow longitudinal slots, oppositely arranged in pairs, thin vanes carried in the rotor slots, the vanes being outwardly movable on the 25 intake and inwardly movable on the discharge sides of the cylinder to divide the crescent-shaped space into pockets, the rotor being bored diametrically between each pair of opposite slots, the

bores communicating with said slots and having a diameter greater than the width of the slots and a depth less than the diameter of the rotor to prevent excessive leakage through the bores,

push-rods of greater diameter than the thickness of the vanes movable in the bores and freely abutting the bases of the vanes to cause each inwardly moving vane to push its opposite vane outwardly to overcome forces tending to retain the latter in its slot, each push-rod likewise preventing material loss of contact of the inwardly 40 moving .vane with the cylinder due to the effect of pressure on the surface of its outer edge.

3. A rotary compressor of the multi-vane type,

3 comprising the combination of a cylinder havrods insures contact with the bases'of the vanes.

and causes them to move outwardly at a uniform rate without tilting.

I claim: 1

' 1. A rotary compressor ofthe multi-vane type,

comprising the combination of a cylinder having intake and discharge ports communicating therei v with substantially on opposite sides, a rotor arbetween each pair of opposite slots, the bores ing intake and discharge ports communicating therewith substantially on opposite sides, a rotor arranged eccentrically therein to provide a crescent-shaped space between'its surface and the wall of the cylinder, the rotor being provided with narrow, longitudinal slots, oppositely arranged in pairs, thin vanes carried in the rotor slots, the vanes being outwardly movable on the intake and inwardly movable on the discharge sides of the cylinder to divide the crescent-shaped space into pockets, the rotor being provided with at least two diametrical bores between each pair ofopposite slots, the borescommunicating with said slots and having a diameter greater than the width of the slots. and a depth less than the diameter of the rotor to prevent excessive leakage through the bores, the bores between each pair'of opposite slots being spaced equidistant from each end of the rotor, solid, cylindrical push-rods of considerably greater thickness than the vanes movable in the bores and freely abutting the bases of the vanes to cause each inwardly moving vane to push its opposite outwardly to overcome forces tending to retain the latter in its-slot, the pushrods likewise preventing material loss of contact of the-inwardly moving vane with the cylinder, due to the effect of pressure on the surface of its outer edge.

CESAR PFEIFFER.

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