US2885143A

US2885143A - Vacuum pump

Info

Publication number: US2885143A
Application number: US525184A
Authority: US
Inventors: Dubrovin John
Original assignee: W M WELCH Manufacturing Co
Current assignee: W M WELCH MANUFACTURING Co
Priority date: 1955-07-29
Filing date: 1955-07-29
Publication date: 1959-05-05
Anticipated expiration: 1976-05-05

Description

May 5, 1959 J. DUBRovxN 2,885,143

VACUUM PUMP Filed July 29, 1955 2 Sheets-Shea?. 1 v

IN VEN TOR.

United States Patent O VACUUM PUMP John Dubrovin, Chicago, lll., assignor to W. M. Welch Manufacturing Company, Chicago, Ill., a corporation of Illinois Application `luly 29, 1955, Serial No. 525,184

Claims. (Cl. 230-153) The present 'invention relates to rotary oil sealed vac- 'uum pumps for the production of extremely high vacuums, and has to do particularly with a pump of the type disclosed in my earlier Patent No. 2,337,849,wherein the rotor is provided with outwardly spring-pressed vanes in sliding engagement with the surrounding wall of the stator and wherein the rotor is eccentrically mounted in the stator and turns in an arcuate seat in the latter, which seat has the same radius of curvature as the rotor and is jdivided into two separate sealing areas.

The purpose of the invention is to increase the eflivciency of a pump of this type by incorporating in the same new and improved means for preventing pressurecondensed vapors in the discharge or wet section of the pumping 'chamber from being carried over in the iilm of :lubricating oil from that section into the intake section ,past the two-part seal present between those sections, also for coninuously volatilizing and removing 'from'the 'dis- 'charge section of the pumping chamber the vapors vwhich tend to condense and accumulate in the end of that section.

The invention resides in the provision for this purpose of novel venting means, in operative association with the two-part seal and also with the discharge section of the ,pumping chamber, which venting means permits of the introduction of air or other volatilizing'uid at such times and in such quantities as to eliminate in large measure the lharmful eiiects of condensible vapors in the pump.

4One specific object of the invention is to provide an intermittently operating yair duct system of .new and im- Lproved construction and operation for 'volatilizing and returning to the discharge section of the pumping cham- ',ber anycondensed vapors which are carried over from ,that section with the ilm of lubricating 'oil past the first VApart of the two-partseal.

`Another specific object is to provide an intermittently operating air duct system of new and improved construcftion and operation for volatilizing and removing 'from the discharge section of the pumping chamber the vapors which tend to condense and accumulate in that section.

While vthe foregoing statements are indicative in a genyeral way of the nature of the invention other objects and advantages will be apparent to those skilled inthe art -upon a full understanding of the construction, arrange- .ment and operation of the vapor volatilizing air admission means incorporated in ythe pump.

A preferred embodiment of the invention ispresented .herein ffor the purpose of eXemplitication, but it will of course beappreciated that the invention is susceptible of incorporation in other structurally kmodied forms com- `ingfwithin the spirit of the inventionand thescope of the 'appended claims.

In the accompanying drawings,

Fig. l is asection view of a pump constructed in accordance with the invention;

Fig. 2 `is 4asimilar view, showinglthe rotor of the lpump alfter'ithas 'advanced v`from the lfpositionrshownlin Fig. `1

Vexhaust port in a vapor state.

into a position in which the air admission or venting means for the two-part seal and for the discharge section of the pumping chamber is in venting position;

Fig. 3 is a similar view, showing the rotor kafterit has passed the venting position;

Fig. 4 is a similar view, with the rotor removed in order to show the channels behind the same in the side wall of the stator;

Fig. 5 is a fragmentary radial section, taken on the Fig. 6 is a similar section, taken on the line 6-6 of Fig. 2.

Oil sealed vacuum pumps are vulnerable, particularly at low pressures, to thecontaminating effects of condensible vapors, and it is therefore desirable in such a pump `to create and maintain a condition in which the harmful 'effects of those vapors are substantially eliminated. Hereltofore it has been proposed to do this by admitting a small amount of relatively dry air into the pumping chamber, which air upon admission will reduce the compression ratio required to open the yexhaust port and will act as a vehicle above the dew point of most of the vapors being condensed to carry at least part of the same through the But no air introducing means Ahas been'devised for a pump of the type with which this invention is concerned ywhich has given satisfactory results.

With the venting means of the present inventionwhich is characterized by a simple intermittently acting valve-like arrangement which affects through ythe air iri- 'troduced not only the condition of the condensed vapors in the discharge or wet section of the pump chamberbut also those in the seal as well-excellent resultshave been obtained.

The invention is shown incorporated in theroughing stage of a two-stage pump of the type disclosed in my earlier Patent No. 2,337,849, but the invention can also be used in a single-stage pump. The roughing stage illustrated in the drawings includes a hollow generally cylindrical stator 10 anda cylindrical rotor 11, which rotor is eccentrically positioned in the stator and is provided with two outwardly spring-pressed vcircumferentially spaced vanes 12 lfor sealing engagement with l'the :sur-

rounding wall 13 of the stator. The wall 13 of the stator `chamber-17, whichchamber terminates at -opposite sides of the arcuate seat 14 and is in all positions of the rotor divided bythe vanes 12 into two sections or segments. An intake port 18 is provided in the stator 10 at'the vacuum end 19 ofthe pumping chamber v17, which intake port in a two-stage pump is connected lwith the discharge port (not shown) of the iinishing stage and in a singlestage pump is connected `by ya nozzle (not shown) with the vessel to be evacuated. A discharge port 20 is pro vided in the stator 1t) at the compression end 21 ofthe pumping chamber l17, which compression end is some- `times referred to as the wet segment Aof Ithe pumping `the compression -end of the chamberiandinto a Acircumferentially separated second sealing area `24 'at the Va`C- num-endrof the chamber.y

ossature sise walls zs er me stam 1s is provided .th a channel 26 which communicates at one end 27 the transverse groove 22 which separates the sealing 23 and 24 and at its other end 28-with the pumping ber at a point in thelatter which istin all positions olf `from communication` with the inport 1l by at least one of thezvanes 12. The channel is intermediate its ends with a branch chan- 29whichterminates at 30. A conduit 31 for air or lluid opens through the face of the side 25 of the stator 10 at 32, in closely spaced relation 30 of the branch channel 29. This conduit 31 `from a point outside the pump `through the side 25o! the stator and its end 32 is normally sealed ot rclosely mating side wall 33 of the rotor. lside wall 33 of the rotor 11 is provided with two small cireumferentially spaced `cavities 34 which are of such shape and size as to span momentarily both the end 32 of the air conduit 31 and the end 30 of the branch channel, 29 during the rotation of the rotor. When either one of the cavities 34 moves into register with the

ends

32 and 30, as shown in Fig.` 2, it places the branch in communication with the air conduit 31, withtthelresult that both the` then relatively large section of chamber in which compression is progressively taking place andthe groove 22 between the sepsrstedsealingareas 23 and24atthearcuate seat 14 are subietitetl` to the air which is momentarily permitted to enter through the conduit 31.

The conduit 31 is connected, outside the pump, to an upstanding tube 35. The tube 35 is threaded at its lower end into a hollow tting 36 and is provided at its upper end with. knurled cap 37 hy means of which the tube can be'turned in either direction to raise or lower the tube with respect to the tting. Outside air enters the tube 35 through a hole 38 in the side of the tube, which is shieldedby a skirt portion 39 of thecap, and passes `downwardly through the center of the tube. A plug 43, which is secured in the lower end of the tube 35,` is` tipped with a centering ball 41, which ball is downwardly through a slot 43 in one side of the plug 40, and upwardly past a checkhall 44 on a valve seat 4S. and then downwardly again through another slot 46 in the opposite side of the plug 40. After leaving the slot 46 the sir continues downwardly past the 41throughabore47inthecenterofthe where it finally` enters the conduit 31. v When the pump is at rest the tube 35 is preferably srrewedrlowuinordertocloseotlcosnpletelytheairy conduit 31, whereby kto prevent discharge through the tnbeofanyoilwhichhasaccumulatedinthepumping enter, and any desired adjustment can therefore be made to condom with the conditions under which the pump is gli a,sss,14s

for dividing the pumping chamber 17 into two sections,

and as provided in its side wall with two cavities 34 for vplacing the inlet conduit 31 .in communica tion with the channel 26 in the side wall of the stator-it will be understood that more than two vanes may be employed, which will divide the pumping chamber into a corresponding number of sections, in which case a corresponding number of cavities will also be employed, with the vanes equally spaced about the periphery of the rotor and with the cavities located in the side wall of the rotor intermediate the vanes.

The pump and the venting means for the same operate as follows:

In Fig. 1 the rotor 11 is in a position in which both of the vanes 12 are at an angle of about 90 degrees with respect toa radius extending from the center of the shaft 15 to the center of the sealed seat 14. In this position of the rotor, the section of the pumping chamber or stator cavity between the front vane and the rear vane represents the largest volume that can exist between the vanes. And in this position, for each cycle (there being two cycles to each complete revolution of the rotor), `the pressure in the section between the two vanes is at the lowest value that it will reach from this point on to the end of the cycle. In other words, as the rotor 11 continues to move the space in this section will progressively grow smaller, with a consequent increase in the pressure.

After the rotor leaves the position shown in Fig. l and before it arrives at the position shown in Fig. 2. the compression in front of the first vane will be in a very much more advanced state. Without the vented exhaust of the present invention the small and progressively decreasing size ofthe segment between the front vane andthe seal 14, which segment contains condensible vapors in addition to the oil with which the pump is sealed, and which is known as the wet segment, would result in the occurrence of rapid condensation of those vapors. These liquids and all other condensates, under this compression stroke, would not only be forced out through the exhaust port but would also be forced into the seal by the impelling force of the vane and carried through the seal between the rotor and the stator. But with the venting means of the invention the amount of vapors condensing in this final or wet segment of the pumping chamber will be materially reduced and those which are carried over into the seal with the oil will be liberated between the two sealing areas of the seal and returned throughy the channel 26 to the compression section of the pumping chamber.

In Fig. 2 a more advanced position of the rotor is shown. In this position completion of the compression stroke of the first vane has been reached with the arrival of that vane at the discharge port, while the compression in the section of the pumping chamber, known `as the compression section, in front of the second vane has increased but little, due to the but slight reduction in the size of that section, with the pressure in the section still below atmospheric pressure. While the compression stroke of the second vane is still at this extremely early stage, the air conduit 31 is momentarily placed in communication with the branch channel 29, whereupon air will rush in and will enter the compression section of the pumping chamber at a point approximately 18.0 degrees removed from the intake port. Some of the sir will at the same time pass upwardly in the channel 26 into the transverse groove 22 between the

sealing areas

23 and 24. Further rotation of the rotor will, of course, cut off the supply of air.

The air which enters the compression section will volstilize any then condensed vapors in that sectiont or an appreciable amount of the same, and will permit them to be evacuated as a mixture of vapor and air through the discharge port, the air becoming a vehicle to carry olf such vapors.

The air which enters the vapor section may be ordinary outside air, at room temperature, but it will be appreci. ated that the drier and cooler the air the better the results. If desired. air which has been dried chemically,

message er-ee'e'ied 'Farr which fhas been suitably treated, @may be introduced.

L'Affter the rotor `leaves the position yshown `in Fig. 2 fand ibefore "it arrives at the position shown Iin Fig.' #3,

the yfront vane will sweep across the discharge port and j ltenter the seal. Some of the oil in the'nal "or wet `segment of the pumping chamber will be forced into the 'seal 'with whatever condensed vapors remain and `r'when *these condensates reach the transverse groove Z2 they be liberated in the channel 26 and returned through that channel'to the compression section ofthe chamber. In this way, volatile liquids are immediately recycled to the compression section of the chamber land 4again exposed to the drying air which has ybeen permitted ito :enter that'section.

yIn rfFig. 3 a 4still more advanced position of the rotor is 'fshown, in which the frs't vane has ypassed the ytransverse groove 22 in the seal and is about -to begin Lthe next cycle. In the travel of this vane beyond the transverse groove all 'that remains "in A'front of 'the 'vane is a minimum quantity of dry oil, which iscarried across the sealingarea 24 by the mechanical motion of the rotor, 'since all o'fthe'condensate-wetted and'excess oil in'front o'f rthe vane Will have been `drawn back into `the vcompression section of the pumping chamber in front of the next vane.

While, as previously indicated, the invention is especially applicable to a pump of the type disclosed in my earlier Patent No. 2,337,849, it can also be incorporated in pumps of other types.

I claim:

1. In an oil-sealed vacuum pump of the type characterized by a hollow generally cylindrical stator, a cylindrical rotor which is eccentrically positioned in the stator and is provided with a plurality of outwardly springpressed circumferentially spaced vanes for sealing engagement with the surrounding wall of the stator, an arcuate seat in said wall of the same radius of curvature as the rotor, in which seat the rotor turns, a crescentshaped pumping chamber between the stator and the rotor, which chamber terminates at opposite sides of the arcuate seat and is in all positions of the rotor divided by the vanes into a plurality of sections, an intake port adjacent the vacuum end of the pumping chamber, a discharge port adjacent the compression end of the pumping chamber, a transverse groove in the arcuate seat, which groove divides the seat into a sealing area at the compression end of the chamber and a circumferentially separated sealing area at the vacuum end of the chamber, and a channel in one of the side walls of the stator, which channel has a portion which in all positions of the rotor is covered by the mating side wall of the rotor, and which channel communicates at one of its ends with the transverse groove which separates the two sealing areas, and communicates at its other end beyond said side wall of the rotor with the pumping chamber at a point in the latter which in all positions of the rotor is sealed oi from the intake port by at least one of the vanes; the provision of an inlet conduit for air or other volatilizing uid, which conduct leads from a point outside the pump through the said side wall of the stator and terminates in an end which in all positions of the rotor is covered by the said mating side wall of the rotor, and a plurality of circumferentially spaced cavities in the said side wall of the rotor, which cavities intermittently move into register with and span the end of said inlet conduit and a part of said covered portion of said channel during the rotation of the rotor.

2. In an oil-sealed vacuum pump of the type characterized by a hollow generally cylindrical stator, a cylindrical rotor which is eccentrically positioned in the stator and is provided with a plurality of outwardly spring-pressed circumferentially spaced vanes for sealing engagement with the surrounding wall of the stator, an arcuate seat in said wall of the same radius of curvature as the rotor,

fin'which seatt'he :rotor u'ms, y'a crescent-shaped pumping Kchamber vbetween-the:statorland therotor, which-chamber t'ermi'nates at'oppositesides 'of `the arcuate seat and :is 2in 'all positions 'of ythe rotor divided fby fthe vanes into a lplurality Aof sections, van intake port adjacent .the vacuum -end Vof fthe ipumping chamber, a `discharge port adjacent the compression lend Ioffthe pumping chamber, and `a channel in onefof fthe side `walls of the stator, which channel has a portion which rin all positions of the rotor is covered fby the mating -side lwall of the rotor andaniother portion which communicates lwith 'the pumping 4chamber I-at-a pointin the latter 'which in all positions-'of the rotor is sealed off fromtheintakefport byat-'least one v"of the vanes; 'the provision of an inletconduit for airor other volatilizing (fluid, lwhich conduit leads froma point 'outside thepump Vthrough the said side Wall of the stator land 'terminates 'in lan fend which in all positions -of the rotor is covered by the said mating fside `-wall Iof 'the vro't'or,-and'tneans movable vwith the 'rotor "for intermittently `placing the end ofsaid inlet conduit in communication 'with --tlie firstmentioned portion of said Ichannel Aduring 'the'rota'tionofftherotor.

:3. lIn an oil-sealed yvacuum pump of the type vcharacterized yby Va lhollow 4generally cylindrical stator, -a cylindrical rotor which is eccentrically positioned in the stator and is provided with a plurality of outwardly springpressed circumferentially spaced vanes for sealing engagement with the surrounding Wall of the stator, an arcuate seat in said wall of the same radius of curvature as the rotor, in which seat the rotor turns, a crescentshaped pumping chamber between the stator and the rotor, which chamber terminates at opposite sides of the arcuate seat and is in all positions of the rotor divided by the vanes into a plurality of sections, an intake port adjacent the vacuum end of the pumping chamber, a discharge port adjacent the compression end of the pumping chamber, and a channel in one of the side walls of the stator, which channel has a portion which in all positions of the rotor is covered by the mating side wall of the rotor and another portion which communicates with the pumping chamber at a point in the latter which in all positions of the rotor is sealed olf from the intake port by at least one of the vanes; the provision of an inlet conduit for air or other volatilizing luid, which conduit leads from a point outside the pump through the said side wall of the stator and terminates in an end which in all positions of the rotor is covered by the said mating side wall of the rotor, means movable with the rotor for intermittently placing the end of said inlet conduit in communication with the iirst mentioned portion of said channel during the rotation of the rotor, and means connected to the inlet conduit for regulating the effective size of the same.

4. In an oil-sealed vacuum pump of the type characterized by a hollow generally cylindrical stator having ilat parallel side walls, a movable pumping member in the stator having at parallel side kwalls which in all positions of said member are in atly sealed engagement with the side walls of the stator, a pumping chamber between the stator and the pumping member, which chamber progressively increases and decreases in volume during the movement of the pumping member, an inlet port which communicates with the pumping chamber only While the latter is increasing in volume and is closed o from the pumping chamber fwhile the latter is decreasing in volume, a discharge port which communicates with the pumping chamber only while the latter is decreasing in volume and is closed off from the pumping chamber while the latter is increasing in volume, and a channel in one of the side walls of the stator, which channel has a portion which in all positions of the pumping member is covered by the mating side wall of the pumping member and another portion which communicates with the pumping chamber only while the latter is decreasing in volume; the provision of a con- 1m kl' air orothervolntilizinl thoszpnmpingtchamber, conduit extendlom la outsidethe pump dlroughthesaidgside will of the im andterminatesinan enduwhieh inrallpositions pumpnzmembenis cuveredby the said mating ofsaidmember are in daily Sealed engagement 8 miie thehun is increasimin" volume. and mhannd in one of the side walls of the stator, whichchannel lhas'fa portion which* in allPQitiQDS-Of Pmi!!! .memberdsfooveredbythe mating side walljo the pumpanothenportion with theapuinpius` chamber only while themlntter` messing `iii-william the Provisionof il` wnduilllfor introducing air or other'` volatilin'ng `fluid into pumpihm chamber, which conduit extends from a point outsidepthelpump through the said aide wall of the and terminates in an end which in all Position#` ofhthe is covered by the said .wall ofI pumping member, and meansmovablewith itheJmnrliiilruz member foryplacins the end of nids@- duit in communication with said channel imilylwpvhile the; pumping chamber is decreasing in volume; consisting lofa cavity `in the `Pumping member;

Refwww in the me of@ mi UNrrED srATEs PATENTS "jz,`191,s4s" y Gases Feb. 2o. 1940 2,337,849 Dubrovin Dec. 28. 194@