US2628770A - Vacuum pump - Google Patents

Description

Feb. 17, 1953 H. G. BOWERING I 2,628,770

VACUUM PUMP Filed May 16, 1950 5 Sheets-Sheet 1 H. G. BOWERING VACUUM PUMP Feb. 17, 1953 5 Sheets-Shet 2 Filed May 16 1950 Feb. 17, 1953 H. G. BOWERING 2,628,770

VACUUM PUMP Filed May 16, 1950 5 Sheefcs-Sheet 3 i 7 5' V E I5 6'0 1 I 45 f 48 ,/6 fl/ ea lab 1220882303 Heavy ahboweaiiifig,

Feb. 17, 1953 H. G. BOWERING VACUUM PUMP Filed May 16, 1950 5 Sheets-Sheet 4 Feb. 17, 1953 H. G. BOWERING VACUUM PUMP 5 Sheets-Sheet 5 Filed May 16, 1950 Hezzzfy G.Bowez4iazg, a C2 Patented Feb. 17, 1953 VACUUM PUMP Henry G. Bowering, Needham, Mass., assignor to Kinney Manufacturing Company,

Jamaica Plain, Mass., a corporation of Massachusetts Application May 16, 1950, Serial No. 162,302

6 Claims. 230147) My present invention relates to vacuum pumps and particularly to that type of pump in which two vacuum pumps, arranged in series, are combined as a unit.

It has long been recognized that increased pumping efiiciency, in the region of high vacuum; may be attained by utilizing two vacuum pumps in series. In such an installation, the second pump, frequently termed the second stage? or backing up pump, discharges to atmos'phere and has its inlet connected to the outlet of the first pump, generally called the first stage or high vacuum pump. a

The advantages of such an installation are that the outlet region of the first stage pumpis maintained at a low pressure, between 15 and 20 microns, for example, which pressure the second stage pump is adapted to maintain efiiciently and that this same function of the second stage pump is effective to remove dissolved or entrained gas or'jboth from the sealing oil for the first stage pump which is discharged through its outlet into the reservoir for that oil, exposed to the inlet of th'second stage pump.

While separate pumps may be hooked up in series by suitable air-tight piping that is adapted to remain air-tight when subjected to pump vibration, the usual requirements for pumps adapted to maintain pumping efliciency in the region of high vacuum are best served by combining such pumps in a single unit. While such pumps have proved highly satisfactory in use and eliminate leakage attributable to vibration, the fact that the first and second stage pumps have a common wall results in troublesome interpump leakage and it is to the elimination of that factor and to a general improvement in pumping efficiency that this invention is primarily directed.

Each of the pumps which I combine in series is of the type which has an eccentric rotatable in a plunger and which is caused thereby to sweep its cylinder. The plunger includes an arm slidably guided in a rotatable pin so that the arm reciprocates relative thereto as the plunger sweeps its cylinder. The arm is effective to ensure that at all times, the pump inlet and outlet ports are never in communication with each other and hence the length of the arm is equal to that of the cylinder requiring that the length of the slide pin be greater than the length of the cylinder.

Where such pumps have been combined as a unit, the casing of that unit included a main casting having a transverse wall common to both pumps and those parts of both of the faces of that wall that established ends for the alined cylinders and sockets for the pins were machined. Prior to my invention, the pin sockets were in alinement and inter-pump leakage through the pin sockets resulted.

"Such leakage is attributable to several factors. Among these may be noted that the common wall, being located in the middle of the casting, was difiicult to test for porosity, actual pin holes or sponginess. In addition, the length of the slide pins required that their sockets extend farther into the common wall than the recesses established by the machined areas thereof that define cylinder ends. As a consequence, it 'was necessary to have the common wall relatively thick in order to ensure adequate stock between the alined pin sockets even though such a wall was excessively thick between the cylinder ends. By that, I mean that the common wall of such a casting was appreciably thicker than other walls thereof which substantially increased the likelihood of its being porous. In the production of metal castings, if the casting walls are not ap-' proximately uniform, the thicker wall or walls,

- particularly if internal, are much more likely to be unsound than when wall uniformity exists. Thus, with a common wall of optimum thickness between the machined areas, there was, between alined pin sockets, an inadequate amount of metal, even if sound without making the casting excessively heavy. The expedient of increasing wall thickness to ensure sufficient metal between alined pin sockets for a barrier against interstage leakage, increased the chance of the casting being unsound between machined areas and pin sockets. These factors, while present in all units, regardless of size, are particularly troublesome with small units.

In accordance with my invention, I combine such pumps as a unit with the slide pin and sockets of one pump being located on the side of a center line through the axis of the pump cylinder that is opposite to the location of the slide pin and sockets of the other pump with reference to that line. the pin sockets results in my being able to insure that each socket is backed by adequate stock, preferably including the unbroken skin of the opposite surface of the casting without an excessive wall thickness between the cylinders. Another important consequence of pin spacing in accordance with my invention is that vibration is minimized.

In the accompanying drawings, I have shown an illustrative embodiment of my invention from The ofiset relation of which these and other of its novel features and advantages will be readily apparent.

In the drawings:

Fig. 1 is a partly sectioned side view of a pumping unit in accordance with my invention.

Figs. 2 and 3 are sections along the lines 2-2 and 33, respectively, of Fig. 1.

Fig. 4 is afragmentary section along the lines 44 f Fig.2;

Fig. 5 is a fragmentary section along the lines 55 of Fig. 4.

Fig. 6 is a top plan view of the unit, partly sectioned to show the details of the circulating systems for the sealing oil.

Fig. 7 is a partial horizontal section through the shaft seal, and

Fig. 8 is a section along the lines 8-8 of Fig. 3.

In the embodiment of my invention shown in the drawings, I have indicated at W acasting having heads II and I2 bolted to its first stage and second stage ends, respectively. A cylinder. cover. I3 is similarly secured to one of its sides. For convenience, I" have indicated generally the first stage pump and the second stage pump at 14" and 15 respectively;

The casting l0 hasits first stage pump cylinder [6. axially alinedf with the second stage pump cylinder [57; A transverse wall It separates the cylinders, l6; and I1" and, freely receives the" drive shaft l9; which is supported" by; bearing units and carried, respectively, by the heads- 11' and l2. The head H has av cap 22" attached to itwhile the head I? has a cap 23.. and a shaft sealf attachedthereto, thehousing; for which is indicated; at. 24. Theshaft l9 protrudes from the housing 24f to be connected to any suitable drive;

Eccentrics 2.5"and 26 in the cylinders l-Gand' I1; spect vely, rekeyedto. thesha t Wand Spaced 180 apart and the wall 18, is recessed on its secondystage side to, receive. the shaft seal '27.

With reference, to. e rst stag p p it.

will be, noted from Fig. 2;, that the casting I01 to beexhausted. Spaced arcuate supports 31land' 3 I. define a. passa eway, betweent inlet. chamb ll Z8, and the cylinder l6;

Thewall'part 32,01 the cylinder lfiiisspacedga substantial, distance. inwardly oil the cylinder cover I3 and includes a lip or dam 33' extending upwardly in spaced relationship to the wall 34 of; the inlet, chamber 2:8; the lower part of" which establishes, the arcuate support 3|; The dam 33' is on the opposite side of the perpendicular through the cylinder axis while the extremity'35 of the wall part 32fis substantially in the plane of the, wall" 34'. I thus provide an L-shaped outlet- 36 opening into the cylinder; L6 in thezone of that: perp ndic r and nte t e passagfiway between the inlet chamber 28- and the cylinder l6- definedby the supports30 and' 3:1. This enables the outletj36. whichis preferably a cored passage- Wamto be qfir t v y large; size ensuring effective gas fl'OW, and at the sametime have such a small; directopening into the cylinder Hi. that it can beblocked by the rotary displacing means; later to be detailed, onceon each rotation offthe shaft I9;

The wallpart' 32, the dam 33; the wall' [8; the bottom. part Illa oi. the. cast ng, In... e castin end wallfi]. (see Fi 6);..and. the. cylinder cove r,

l3 define, in the assembled unit, a reservoir 38 for the sealing oil for the first stage pump 14.

With reference to the second stage pump l5 and, as may be best seen in Fig. 3, it will be noted that the casting It! establishes an inlet chamber 39 above the cylinder l1 and on the same side of the perpendicular to the axis of the cylinders as theoutlet 36.. from thecylinder Iii-and on the oppositesideof that perpendicular, relative to the inlet chamber 28. Spaced arcuate supports 49 and 4H define a passageway between the chamber 39 and the cylinder ll. The wall it has a port t2 effecting communication between the outlet side of. the, first, stage pump [4 and the inlet chamber 39 of the second stage pump l5 and the lower edge of the port 42 is an appreciable distance below the to of the dam 33.

The wallpart- 43 of the cylinder I! is spaced a substantial distance inwardly of the cylinder cover [3 and joins the wall 44 of the inlet chamber 39, so that, they, the cylinder cover l3, the bottom part 0b of the casting Hhthe adjacent end 45, of the, casting I0? (see Fig. 6), and the wall [8 establish, in the assembled unit, a reservoir, 46 for the sealing oil for the second stage pump [5. Thewall 44" includes a baffle 41: disposed towards the. cylinder cover [3 and the cylinder cover, l3 has abaflle 48 terminating in a reversely disposed flange 49 disposed closely adjacentthe intermediate part of the upper-surface of the baflle 4'1; Abovegthe baflie 48, the casting Hi has a threaded port to receive the outlet conduit 59to theoil trap-,generally indicated at 5!,

and which is open to atmosphere.

It will be appreciated that the cylinders l9 and. I? are carefully machined as are those portions of the wall l8 and the heads- H and F2 that constitute the ends thereof;

The arcuate supports 30 and 31-, and" 40 and The; laterally spacedrelationof the'inlet'chambers 28 and 39'enables theslide pins- BZ-and 53 tobe, so; spaced thatgtheirsockets- 59 and 57- do not even overlap,,a1though' each of said sockets is shown as having arelatively small area of overlap with the machined cylinder end on the opposide: side of, the wall I8: This arrangement has the advantages that" the major portionof themetal skin on the wallsurface'oppositeeither of those sockets. is not. broken and hencev ensures against inter-pump leakage between adjacent'pin sockets, and the;wa-1l| 8 isof satisfactory thickness in the-zone of ea-ch" socket withoutbeingtoothick in, the Zone of the; cylinder ends;

With refer,ence to the first stage pump 14; the

eccentric 25 is rotatable within a, plunger 58 which has an integral arm 59 slidably'extending through the slide pin 52'; The arm 59' is hollow to provide a conduit 69? open at its upper end while at its, lower end, it' has a port 611 with reference to which the pin: 52 serves as a valve as the plunger 58" sweeps the cylinder lB thereby to block the inlet chamber 23 therefrom as the plunger 58: passes and blocks the outlet port 36so that the chamber 218' andQthe outlet port, 3.6.v are never, interconnected.

.means, generally indicated at 6?, and which may be seen in Figs. 3 and 8. ,In practice, that portion of the wall part it in which the outlet ports 56 are located is machined and a relatively thin valve plate 68 and a relatively thick valve block 69 are freely positioned thereon by valve guides It. The valve guides "it are of substantial length and have their upper ends formed as at H to be engageable as by a socket type of wrench.

Threaded into the cylinder cover 3 are adjusting screws l2 chambered to receive the ends ll of the valve guides it. Compressed between the valve block t9 and the adjusting screws 72 are valve springs it held in place by the guides lil. Each adjusting screw '52 has a threaded portion '14 of reduced diameter, the extremity lb of which is shaped for wrench engagement and threaded to its portion M is a nut it, to which is threaded a cap nut Eda. Valve adjustments may, accord.- ingly, be readily effected since, when the nuts 75 are removed, the extremities it of the adjusting screws protrude through the cylinder cover IS. The cylinder cover it has a window '5? by which the oil level in the reservoir 33 can be seen and plugged drains i8 and it for the reservoirs 38 and 4 6 of the first and second stage pumps, respectively. An advantage of my units is that the cylinder covers it, which define a wall of both reservoirs, may be removed to expose the entire interior of the reservoirs 38 and at to enable them to be thoroughly cleansed.

As may be seen in Fig. 6, the casting end wall 31' has a port til which registers with a port 8| in the head i i to enable oil to flow from the reservoir 38 into the needle valve controlled conduit 82 and through that conduit to the bearing unit 2d. The casting end wall 45 has a port 83 which registers with a port St in the head I2 which is in communication with the needle valve controlled conduit 85 thereof to deliver sealing oil fromthe reservoir 4'65 to the bearing unit 2 l Each of the conduits 82 and 85 has a seat 85 engageable by the needle valve head ill, the plug part 88 of which is threaded into the outer end of that conduit and partly protrudes therefrom. The exposed extremity of the needle valve part 88 has a kerf St to enable valve adjustments to be made with a screw driver and threaded thereon is a nut 91!, exteriorly threaded to receive the cap nut 99a. I have found the shaft seal shown in Fig. '7 to be particularly effective. As shown in that View and in Fig l, a seal seat 9! and ring 92 are clamped by the housing 24 against the head l2. Seal washers 93 are backed by the seat 93 and the opposite end of the housing 24. Adjacent each washer s3 is a washer engaging seal 94 and a shaft enga ing seal 35 which are confined by a shouldered element 9%. The elements 96 are yieldably spaced by the spring 9?. An oil cup 98 serves to provide a sight indication of the oil supply for the shaft seal. I prefer that the oil supply for the shaft seal be independent of the oil circulating system for the second stage pump l in that; it will remain free of contaminants.

From-the foregoing description, the operation of my unit will be apparent. At the start up, accumulated oil in the cylinders is pumped out making necessary the bafiles between the oil reservoir 33 and the oil trap 5| to prevent oil from being discharged therethrough. Thereafter, the oil level in each reservoir is stabilized and the second stage pump i5 effectively backs the first stage pump it and de-gasses the oil in its reservoir 38.

The second stage pump i5 is effective to maintain the pressure in the zone of the outlet and reservoir of the first stage pump I 3 in the region of a few microns, 15 to 20 microns for example. Any leakage or any gas entrained in the sealing oil of the second stage pump 55 has a negligible eifect on the eificiency of that pump at that pressure but would seriously affect the efficiency of the first stage pump l4.

Since the second stage pump i5 discharges to atmosphere and since the oilin its reservoir 46 is not positively dc-gassed, some gas is always present to limit its eificiency. Inter-pump leakage through the pin sockets in the wall I 8 is eliminated in accordance with my invention because of their offset location. In the embodiment of my invention shown in the drawings, each pin socket in the wall 18 overlaps the machined cylinder ends established by that wall. With reference to the first stage pump it, however, the location of the pin socket 51 of the second stage pump 15 is such that it is at all times blocked from the inlet chamber 28 and is in the zone of the outlet 36 which is in direct communication with the inlet chamber 39 of the second stage pump. With reference to the second stage pump it, the location of the pin socket 556 of the first stage pump I4 is remote from its valve controlled ports 86.

It is essential that the outlets of pumps, such as the pumps l and I5, be located as close to the slide pins as possible. With pumps in accordance with my invention, this essential does not result in inter-pump leakage via pin sockets with the consequence that increased pumping efliciency in relation to the size or" the unit is ensured.

From the foregoing, it will be appreciated that vacuum pump units in accordance with my invention are characterized by economical production due to the nature of the castings Ii), increased pumping efiiciency in the region of high vacuum because of the elimination of inter-plump leakage, lowpower consumption and decreased vibration in operation, and ease of service as to valve adjustments and reservoir cleaning.

What I therefore claim and desire to secure by Letters Patent is:

1. In a high-vacuum two-stage pumping unit, the combination of a housing enclosing two axial- 1y alined cylinders, one for each stage, said housing including a cast metal main component in which an integrally cast metal wall separates said cylinders and has opposite parallel machined surfaces which are the proximate end boundary surfaces of respective cylinders; a shaft extending through said Wall and axially through said cylinders; and rotary displacing means arranged to be actuated by said shaft, one in each of said cylinders and ach including an arm and a slotted oscillating cylindrical pin, through which pin said arm reciprocates as the shaft rotates, each face of said wall being intersected by a socket which receives an end of a corresponding one of said pins, each socket extending part way through said wall, the axes of said socketsbeing offset from each other on an are about the shaft axis by a distance materially exceeding the suih -of the radii of the socketsso that the sockets are wlde' ly spaced in the zone of their closest'apprdach andthe depthof a single socket determines the thick ness of the metal barrier be'tweenthe' end ofi the socket for either cylinder and the proximateend of the" other cylinder.

2. In a high-vacuum two stag'e' pumping unit; the combination of a housing enclosing two'axially alined cylinders, one foreachst'age} said housing includin a cast metal main component which an integrally cast metal wall separates" saidc linders and has opposite parallel machined surfaceswhichare the proximate end boundary surfaces'of respectivecylinders; a shaft extendingthrough saidwall'and axially through'saidcylinders; and rotary displacing means arranged tobe actuated by said shaft, one in each of said cylindots and each including an arm'- and a slotted oscillating cylindrical pin, through Which'pin said arm reciprccatesas the'shait rotates, each face of said wall being intersected by-a socket which receives an end of a corresponding one of said pins, each socket extending part way through said Wall, the axes of said socketsbeing offset fromeach other on an arc about-the shaft axis by a distancematerially exceeding the sum of theraditof the socketsso'that the sockets are widely spaced in the zone of their closest ap-- proach and the depth of asingle socket determines the thickness of the'metal barrier between the end of the socket for either cylinder and the end-oi the other cylinder, the casting skin on both faces of said Wall being intact except for said machined surf aces-and except where -in tersected by said sockets.

3. In ahigh-vae-uum two stagecpumping unit; the combination of a housing enclosingtwo axially alined cylinders; one for each stage, spacedinlets and outlets-'foreac'h stage; and'areservoir for each stage with which the outlet ofi that stage is in communication, the outlet forone stage being in approximate longitudinal alinement with the inletfor the other stage; saidhousing including a cast metal main component" iniwhich an integrally cast metal wall separates said cylinders and their respective inlets, outletsand'reservoirs and has opposite parallelmachined surfaces Which are the proximate endboundary surfaces of respective cylinders and a portby which thealined inlet and outlet are placed id communication; a shaft extending through: said wall: and axially through said cylinders; and rotary displacing ll'lGZtQSaI'IQHQGd tobe'actuatedby Saidisl1aft,-0ll6 in each-cylinder and each ineluding an arm extending into the-inlet for-that cylinder and a slotted osciliating cylindrical pin through which saidarm reoiprocates' as the shaft-- rotate and a seat for each pin includinga'socket extending-part way through said wall, the-inlets of the respective cylinders being so spaced relative tOZGELChDthEI that the axes of said s'ockets areroiiset' from each other; on an arciabout the: shaft axisby a distance materially exceeding thesum-of the radii of the sockets so that the sockets-- are widely spaced in the zone of theirclosest approach and the depth of a single socket de=- termines-e thee-thickness of the metal barrier. be: tween the) end: of thev socket for eitheri'cylinder-f and the proximate endlof the other: cylinder.v

a. In ahighevacuum tWo-stagapumping: unit; the-combination of a housing,enclosingfirstaand' second axially alined'cylinders for the first and second stage, respectively, said.housiiigiinclude inga cast metal main component inwhich: an

integrally casttmetar wall separates said-cylinders andi has opposite parallel machined surfaces: which are the proximateend boundary" surfaces ofrespec'tive cylinders; a' shaft extendingthrough' said wall and axially through said cylinders; and

rotary displacing means" arranged to be actuatedby saidshaftyon'e in e'ach ofsaid cylinders and" each incliidin'g an arm and a slotted oscillati cylindrical pinpar'allel with said shaft,;throughwhich pin: said am reciprocates as the shaft rotates; each: pin being" mounted in: a cylindrical seat which intersects the corresponding cylinder and terminates in a socket extending. part way through said wall and intersecting" aportion of themachined' surface, the axesof said sockets:

beingiohset from each other'onan are about the shaft axis by a distance materially exceeding the sum of the radii ofthe sockets so thatthe socketsare widely spaced in the zone of their closest ap-- proach and the depth ofa single; socket determinesthe thickness of the metal barrierbe tween the endof the socket for either cylinderand the proximate-end of the other cylinder, the" displacing means foreach stage being disposed relatively" to each other to provide minimum compression in the second stage inthe zone of the'socket for the first" stage pin.

sageway in communication Withthe cylinder of that stage, the outlet chamberfof the firststagebeinglongitudinally alined'with the'inlet chamber of the second: stage, said housing'including acastmetal: main component in which: an in tegrally cast metalwall separates saidcylinders and their" respective chambers: and has opposite of said cylinders and each includingra ported arm and a slott'ed oscillating cylindrical pin parallel with saidshait: through which-pin said arm re natingzih a' socket extending-i part way through saidewall and: intersecting a portion of the ma chinedsuriacatheaxes of said sockets being offsetfromeach other on an'arc about the'shaft axis by a distance lnaterially exceeding the sum of the radii of:the societs so that the socketslare' widely. spaced inthe zone of their: closest ap-- proachz and the: depth of: a single socket de-- terminesrthe thickness of the metal barrier be tween the end of the socket foreithericylinder' and-the proximate end-ofthe other cylinder, the.

outlet passagewayl'for said first stage opening into the first stage cylinder and its inlet passageway. at'their junction, the first stage displacing means and: the pin'and. arm of the first stagesimul taneously'blocking said first stage passageways once in each revolution :of said first stage displacing means;

6. In a high-vacuum two-stage pumpingunit 1 theicombination of a housing ehclosing 'flrst and that stage, the outlet chamber of the first stage being longitudinally alined with the inlet chamber of the second stage, said housing including a cast metal main component in which an integral- 1y cast metal wall separates said cylinders and their respective chambers and has opposite parallel machined surfaces which are the proximate end boundary surfaces of respective cylinders and a port by which said alined chambers are placed in direct communication; a shaft extending through said wall and axially through said cylinders; and rotary displacing means arranged to be actuated by said shaft, one in each of said cylinders and each including a ported arm and a slotted oscillating cylindrical pin parallel with said shaft, through which pin said arm reciprocates as the shaft rotates providing a valve open through a predetermined partial rotation of said displacing means, each pin being mounted in a cylindrical seat in the passageway between its cylinder and its inlet chamber, each seat intersecting the corresponding cylinder, the axes of said seats being offset from each other on an arc 10 about the shaft axis by a distance materially exceeding the sum of the radii of the seats so that the seats are widely spaced in the zone of their closest approach, the outlet passageway for said first stage opening into the first stage cylinder and its inlet passageway at their junction, the first stage displacing means and the pin and arm of the first stage simultaneously blocking said first stage passageways once in each revolution of said first stage displacing means.

HENRY G. BOWERING.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,061,181 Kinney May 6, 1913 1,390,586 Petsche Sept. 13, 1921 1,705,653 Weber Mar. 19, 1929 1,890,572 Dubrovin Dec. 13, 1932 2,215,256 Stoltz Sept. 17, 1940 FOREIGN PATENTS Number Country Date 499,616 Germany June 12, 1930

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