US1890574A

US1890574A - Vacuum pump

Info

Publication number: US1890574A
Application number: US451567A
Authority: US
Inventors: Dubrovin John
Original assignee: Central Scientific Co
Current assignee: Central Scientific Co
Priority date: 1930-05-12
Filing date: 1930-05-12
Publication date: 1932-12-13
Anticipated expiration: 1949-12-13

Description

ne@ 13, 1932. J, DUBRWN 91,890,574

VACUUM PUMP Filed May 12, 19:50 2 sheets-shut '1' J. DUBROVIN -VACUUM PUMP QQ. ,QQ Q s NN Q QQ W w ,QW n@ Nm QN bw um, NN

b. mw! QN @CRN NN QQ Patented Dec. 13', 1932 JOHN DUBROVIN, OF CHICAGO, COMPANY, OF CHICAGO,

ILLINOIS, `ASSIGINOR, TO CENTRAL ILLINOIS, A CORPORATION OF ILLINOIS SCIENTIFIC VACUUM.' PUMP Application led Hay 12, 193.0. Serial No. 451,567.

This invention relates to improvements in vacuum pum s.

It is an obJect of the present invention to provide a simple and effective backing pump 5 in combination with a high vacuum stage and to combine the two so that the backing ump becomes in effect a fore-stage for the igh vacuum cylinder, and to do this without substantially increasing the number of parts required or changingin any material degree the bulk of the pump.

It is an object of the invention to allow better cooling than has heretofore proved possible and to avoid difficulties with the sealing fluid; to secure the rapid outgassing of the oil so that the highest vacua may be quickly attained; to reduce as far as may be practicable the volume of oil necessary for sealing the pump; and to subject this foil continuously to an outgassingv process.

By sealmgl the pump by means of oil channels instead of running it immersed in a tank of oil, I not only materially reduce the volume of oil to be outgassed, but I also expose the outer surfaces of the pump directly to the air and, as a direct result, achieve much lower operating temperatures and a reater capacity for my device. The princip es and details of construction will become apparent from the specification and the annexed figures in which 7 v Fig.` 1 is a vertical, longitudinal section through my device;

ig. 2 is a sectional elevation of the same; 1g. 3 is a section through the pump taken on the line 3-3 of Fig. 2;

Fig. 4 is a section through the pump taken on the line 4-4 of Fig. 2;

Figs. 5, 6, and 7 are diagrammatic representations of the position of the parts in my improved pump in three positions of its operating cycle.

With reference to Fig. 1, the pump is com- 5 posed of a ring section 10, provided with a neck like extension 11 and the

end closure plates

12 and 13. Both the ring and the plates are ground upon their mating surface and the joint thus formed is made as tight J as possible. The ring is provided with a cylindrical pump chamber 14 in which the eccentric 15 aiiixed to the shaft 16rotates.

An inta-ke passage is provided by the bore hole 9, as shown in Fig. 2^.v Connecting with the bore 9 is the intake pipe 61 which is threaded and sealed into the boss 59 on the rng 10. The configuration of the plate 12 provides a housing 17 for the bearing 18. The plate 13 is 19 which provides a bearing for the shaft. The stud is counz'erbored to receive a gland (notshown) which is held in place by the packing nut 21 threaded on the stud.

n eccentric strap 22 surrounds the entire face oi the eccenr'c and bears a blade 23 operatively connected to the strap in some fluid tight manner such as the tongue and groove lock shown. The strap may itself contact with the cylinder wall, as shown on ig. 2, or the eccentric member may be made to do the aci'ual contacting necessary and the strap occupy merely a narrow zone thereon.

A gland 24 adapted to oscillae as the movement of er extending longiudinally across the gland. For machining reasons only, the gland is sectional and is closed by the ca 30. The chamber is divided by the blade into two

pump cylinders

25 and 26 in wh'ch the

pistons

27 and 28, which are here shown as integral extensionsof the blade, operate. he two pumps exhaust into the space 29 which forms the common exhaust passagev for both pumps.

The pistons carry the

ball exhaust valves

32, 32, the balls being seated in the

passages

31, 31. A light retainer 33,v held in place by screw 34, prevents the balls from being dsp.ace

By reference to Fig. 2, it will be seen that the floor 'of (he cylinder 25 forms a sharp angle with the blade and that a portion of it 1s cut away, as shown at 36, Fig. 1, to form the exhaust passage from the rotary stage of the pump. l

- The angular iioor urges a cylindrical valve provided with a hollow stud leaf spring 42 37 against the blade 23. The movement of the valve is limited by the retainer pin 38. The ends of the cylindrical valve 37 are slightly chamfered, as at 40, to provide a bypass through which the oil may pass into t e exhaust passage and into the rotary pump sta e.-

he oscillating gland 24 bears an exhaust valve 39 on its upper exposed area, compose of an upper arcuate spring 41 and a lower These are maintained in position by the screws 43 and stops 44.-

As indicated on Fig. 2, the intake passage 45 tothe pump cylinder 26 leads to a groove 46 which may be in either the mating surface of the ring 10 or of the

plates

12 and 13. An extension of the groove formed by a drilled passage 47 leads up to the shaft 16 and is connected with the

grooves

48, 48 cut on the shaft.

In order to counterbalance the device, it is usuall preferable to hollow out the rotor 15, as is s own at 49. The plate 12 accordingly bears an annular groove 51 cut in its inner face surrounding, ut spaced from the shaft 16. The groove 51 is connected by a groove 52 to the suction space of the pump.

An oil trap member 53 heldin position by the screws 54 forms the cover of the device. A asket 55 is interposed between the trap and pump casing to prevent leaks. The bottom of the trap is broken by a tendin transversely across it, and rising from t e edge ofthe channel are two oil retaining and baflie members 58 and 59 which also extend across the trap. Two oil level regulating nipples 61, 62 with longitudinal passages therethrough 63, 64, are forced into the, bottom wall of the trap. A V-shaped baiile 56 covers the channel 57 and forms a spray hood. A sight glass 65 is provided in one wall of the trap. The bezel 66 drawn up b the screw 67 presses the glass up against the exible gasket 68. The outlet from the ump is provided by the orifice 69.

The Figs. 2, 5, 6 and 7 illustrate the position of the operative parts at intervals in one cycle of the pump.

The operation of the pump is as follows: Starting with the position of the device as shown in Fig. 2, as the shaft rotates in a clockwise direction, the eccentric causes di ferent portions of the eccentric strap to come pro ressively in contact with the cylinder wal Momentarily, there is but one space within the cylinder (Fig. 2) equalizing the gas ressure therein, and then the space is cut 1n two (Fig. 5). Thereafter, (Figs. 6 and 7), the space to the right (ahead of the piston aspirates the gas. The space to the left, hind the piston) compresses it.

i Since the eccentric carries the eccentric stra first to one side, then to the other, the bla e which is a rigid extension of the strap must swing from side to side. Accordingly,

channel 57 ex- `in the gland. The upstroke o d the the gland which forms a stu'mg box preventing the gas on the com ress1on side from mixing with the gas on t e intake side must oscillate andthe blade ride up and down which bears the pistons on its upper end creates a suction in the pump chambers 25 and-'26. The gas Ibein exhausted through passage 36 is un er compression and rushes in to fill the 'space 25.

When the article to be exhausted is nearly at atmospheric pressure, the amount of gas handled by the .eccentric stage is greater than the reciprocating stage can actually pump. Both valves in the reciprocating sta e are accordingly displaced and a constant ow of gas maintained through the passage and piston. However, when vacua of any substantial degre'e requiring a fore-pump are approached, the amount of gas delivere through the port 36 is. not suilicient to overload the chamber and the eiiicac of the forepump then begins to be felt an increases as increasing vacua are obtained.

Because of the great range of both volume and pressure which a vacuum pump commonly encounters, considerable diliiculty has been experienced with valves. The use of a ball valve in the reciprocating piston is, however, particularly helpful since the valve is operated not by the pressure against the seat,

f the blade but by its own inertia and will respond although very small quantities of gas are expelled as the higher vacua are approached. The piston may thus act as a scavenger without unduly compressing the gas in the

cylinders

25 and 26.

On standing, oil seeps into the cylinder. When the pump is started, slugs of oil Iand gulps of air practically at atmospheric pressure pass through the device. A relief valve is thus a necessity. The valve 39 is both a relief valve and a differentially responsive exhaust valve.

When the pressure in the space is high, as when tra ped oil or atmospheric air is passing, the owed spring is forced up and the leaf valve rises on its guide studs exposing a wide slot. As the pressure drops, the leaf valve remains seated, but since it is very thin and flexible (it may even be ta er ground to aid in this effect), it is de ected over smaller and smaller areas. Thus the effective opening of the valve is secured at pressures so low that .operation of a gravity inertia or fixed tension spring valve becomes uncertain.

In order to balance the eccentric to allow high speed operation of the pump, av hollow space in the body of the eccentric is provided. Upon standing, this space will build up to atmospheric pressure and since pumps which are capable of producing very high vacua are nice mechanical jobs, the fit between the yrotor and the

plates

12 and 13 is necessarily close and practically sealed by tween the shaft and `into the high vacuum the oil film therebetween. An evil known as' slipping then may occur,'since the as con-A tained in the hollow slowly leaks into `the high vacuum area. This is prevented in the present pump by the provision of the annular passage 51 (which may be 1n either of the end plates) and the connecting passage A52. The e'ectof this is to add the space within the body of the eccentric to the space to be evacuated and, since the, gas within the s ace is pulled down to the tpressure of the igh vacuum chamberyno slipping can occur.

To` prevent leaks, it is desirable to reduce the pressure diHerential existing between the outer and the inner edges of the mating faces and in 'fact at any joint in the pump where leaks could occur. The channel 46 is accordingly cut into the face of the

plates

12 and 13 or into the ring 10, as may be desired. The channel is connected by the passage 45 to the second reciprocating pump 26 contained in the gland. 'llhe extension of the channel 47 connecting with grooves 48 allows this vacuum seal to be applied to the joint bepacking.

The vacuum in the chamber 26 and the sealing channels 46 is in the order of millimeters. Consequently, the pressure tendlng to make the pump casing leak exists as a gradient between `the outer surface and'the sealing channel. Whatever air leaks into the pump along the joints in the casing 1s consequently trapped in the sealing channel and swept out. rthe residual gradient between the sealing channel and the high Vacnum chamber is small. It will cause no trouble if the joints are well machined and usual sealing precautions are taken.

Upon first glance, it would seem as if no passages were provided through which sealing and lubricating `oil could be led to the moving parts. In this pump, however, all free fits are open oil passages, for it must be remembered that the oil is under a pressure of more than 14 referred to any space below the pistons, that it meets no obstruction of trapped gas, and that it spreads and creeps over every surface.

@il will adsorb gas in considerable quantities whenever it is exposed to a gaseous atmosphere. lf such oil then were admitted chamber, the gas would be delivered up and of vacuum obtainable would dependfupon the freedom from adsorbed gases which the sealing medium enjoyed. In order to pre-` vent such .polluted oil from working into the igh vacuum stage, it is necessary to expose it to a degree of vacuum suflicient to cause it to deliver up the major portion of the gas before it can reach the chamber.

Whatever oil comes in under the valve 39 and passes down the walls of the reciprocatingl pumps into the high vacuum pump chamlbs. to the sq. inch, as'

consequently the degree ber will have been very thoroughly vacuum treated .i by the reciprocating stage. However, there is' another path by wh1ch the oil can get into the high vacuum chamber and that l1s along the joint between the gland andl the casing. It 1s advantageous, therefore, to provide one or more longitudinal channels in the bearing face between the casing and gland and connect these channels to the en-4 trapment channel system 46. It may even prove advantageous to make arcuate transverse extensions to this channel as shown at 71, 72, Fig. 2, so that more oil may be trapped and subjected to vacuum. Whatever oil, therefore, reaches the high vacuum stage has been robbed of the adsorbed gas by this precaution.

pon starting a new pump, it is necessary to pour in through the opening 69 a quantity of oil suliicient to rise up to the top of the nipples 61, 62, and in addition an amount which Willill the sealing channels and sufiiciently seal and lubricate all of the working parts. It will be the tendency of the working parts to squeeze and force out some of vthis oil which will be blown against the baille as a spray, but whatever oil drops olf the balile will cause an overflow of the reservoir and the excess will pass through the channels 63, 64 back into the moving system.

have described my improved design as applied to a vacuum pump capable of producing vacua of very high degree. Such a pump will produce vacua of theorder of l/1.0,000 of a millimeter without difficulty.

It 1s, of course, obvious that the be decidedly useful in other work.

Where high vacua are not desired or a pump for liquids needed, the

channels

51, 52, 45 and 46 are not necessary, and a passage may be drilled through the blade just below the piston so as to cause the two sides of the piston to operate in parallel upon the fluids discharged by the rotary stage.

I do not limit myself to a precise arrangepump will ment, for it is obvious that modifications and rearrangements action is in full herein set forth.

I claim as my invention 1. A vacuum pump of the rotary plunger type comprising a casing and a pump cylinder having inlet andexhaust passages, in combination,an eccentric in the cylinder, an eccentric strap, a blade separating-the inlet and exhaust chambers of the cylinder, operatively connected to the strap, an oscillatmay be made in which the accord with the principles ing gland within the casing forming an oscil' l'ating pump cylinder in which the blade reciprocates, a piston carried by the blade, the inlet passage to the reciprocating stage forining the exhaust passage of the first named stage, and a valve closing the passage.

2. A Vacuum pump of the rotary plunger type comprising, in combination, a plunger haust valve closing Eil r tion, an eccentric in the cylinder,

member provided with \a radial blade, an oscillating gland cooperating with the blade and having a pump cylinder therein, a piston in the pump cylinder, a connection between the piston and the radial blade causing the piston to reciprocate, and an inlet passage to the pum cylinder receiving material discharged by the rotary .plunger stage of the pump. Y l

3. A vacuum pui'np comprising, in combination, a casing having a cylindrical chamber, an inlet thereto, an eccentric rotor in the chamber, an annular piston surrounding the rotor and rovided with a radial blade rigidly atlixed t ereto, a gland adapted to oscillate and in which the blade reciprocates, a cylinder in the oscillating gland, a piston in the oscillating cylinder operated b 1 the blade, an outlet passage lfrom the cylin rical chamber communicating with the inlet to the oscillating cylinder, and a valve in the passage.

4. In a pump of the rotary plunger type, including a casing and a pump cylinder having inlet and exhaust passages, in combinaan eccentric strap, a blade operatively connected to the strap separating the inlet and exhaust chambers of the cylinder an oscillating gland within the casing orming an oscilating pump cylinder in which the blade reciprocates, a piston carried by the blade, the i inlet c passa e being the e to the reciprocating stage aust passage of the first nam stage, a valve closing the passage, and a bypass around the valve through which sealing` fluid may be admitted to the pump chamber.

5. In a pump of the rotary plunger type including a casing and a pump cylinder having inlet and exhaust passages, in combination, an eccentric in the cylinder, an eccentric strap, a. bladeseparating the inlet and exhaust chambers of the cylinder operatively connected to the strap, an oscillating gland within the casing forming an oscillating pump cylinder lin which the blade reciprocates, a piston carried by the blade, the inlet passato the reciprocating stage forming the ex aust passage of the first named stage, a valve closing the passage, inertia valves carried by the piston, and a leaf spring exthe oscillating cylinder.

6. A vacuum pump of the rotary plunger type, comprising, in combination, a casing, a cylinder therein provided with intake and exhaust passages, a hollow eccentric within the cylinder, and an annular eccentric strap surrounding the eccentric, a blade operatively integral with the strap, and a channel in the casing extending from the suction space and intercepting the path swept by the hollow of the rotor whereby the space within the rotor may be reduced to, and maintained substantially at, the-same pressure as that existing in the suction passage of the pump.

7. A vacuum pump of the rotary plunger ing liquid in type, comprising a casing made of joined parts containing a pump cylinder wherein a blade attached to an eccentric strap is caused to operate a reciprocating pump, channels formed in the components of the casing and interposed in the mating face between the joined parts, a sealing iuid within the casing and the channels, a cylinder in the reciprocating stage adapted to outgas the sealing medium, and a connection between the channels and the outgassing pump.

8. In a vacuum pump of the rotary plunger type comprising a casing made ot joined lparts containing a pump ,cylinderv wherein a blade attached to an eccentric strap is caused to operate a reciprocating pump, means for preventing leakage along joints in the casing and packing members which consists oi channels formed in the components of the casing and interposed in the bearings and in the mating faces of the joined parts, a sealthe channels and a connection between the reciprocating pump and the channels for producing a vacuum therein, whereby the pressure gradient tending to cause leaks into the high vacuum space is Inaterially reduced and the sealing liquid is outgassed.

9. A multi-stage vacuum pump of the rotary plunger type comprising a casing sealed against leaks by a liquid, va. high vacuum pump c linder formed in the casing, an eccentric in the cylinder, an oscillating gland journaled inthe casing and a pump cylinder formed in the oscillating gland, means to ap- -ply a preliminary vacuum between the gland and casing and to outgas the sealing liquid before its entrance into the high vacuum cylinder, which consists of channels in the bearing surface between the casing and gland, and a connection to the intake of the oscillating pump cylinder.

10. In a multi-stage vacuum pump of the rotary plunger type, a liquid, a casing, a cylindrical oscillating member journaled in the casing, a pump cylinder formed in the oscillating member, a blade connected to the rotary plunger and caused to reciprocate in the oscillating membei', two pistons carried by the blade, which blade together with the walls of the oscillating member forms two pump chambers therein, one chamber being the exhaust passage of the rotary plunger pump, the other serving to outgas the sealing medium of the pump.

11. In a vacuum pump including a casing wherein the amount of fluid and the pressure at its discharge vary through wide limits, having a xed rotary pump cylinder and an oscillating reciprocating pump cylinder within the casing, the combination of valves in the reciprocating member operated by inertia and an exhaust valve for the oscillating sealed against leaks by cylinder adapted to open a diierent amount i with differing pressures and volumes of the exhausted Huid.

2. In a vacuum pump provided with a piston chamber, a piston for said chamber, an intake and a discharge port for said chamber, a valve for said discharge port,

same, said chamber having an opening for conducting oil from said oil receptacle to said chamber and a baie above said oil retaining' members for defecting` oil splashed from said oil chamber by air discharged through vsaid outlet port into said receptacle.

n testimony whereof I aX my signature.

JOHN DUBROVIN.