US2797043A - Vacuum pump - Google Patents

Description

United States .atent 2,797,043 Patented June 25 19 7 VACUUM PUMP Gordon P. Gerow, Rochester, N. Y., assignor, by mesne assignments, to Consolidated Electrodynamics Corporation, Pasadena, Calif., a corporation of California Application June 16, 1953, Serial No. 362,061

2 Claims. (Cl. 230-45) This invention relates to vacuum pumps and is particularly concerned with pumps operating in the high vacuum range.

Successful operation in the high vacuum range is dependent upon adequate vacuum pumps. In the usual high vacuum operations at pressures below about 100 microns Hg, a combination of vacuum pumps is employed, each of which has maximum operability over a limited portion of the pressure range. Thus a mechanical vacuum pump is employed for the rough pumping operation to reduce the pressure from atmospheric pressure to a few millimeters pressure where a dilfusion pump 'becomes operable. The ordinary diffusion pumps wellknown in the art are very effective for producing a very low pressure, i. e. pressures in the range below 10 microns Hg and particularly below 1 micron Hg. The ordinary difiusion pump, however, does not pump at peak speed in a pressure range above about 1 micron nor does it pump against a high forepressure. It is therefore desirable for certain applications to provide a pump capable of attaining a high ultimate vacuum but capable of operating at peak speed in a higher pressure range and having a higher limiting forepressure than does a conventional diflusion pump.

it is accordingly an object of this invention toprovide a new and improved vacuum pump.

It is another object of the invention to provide a high vacuum pump of new construction capable of operating at peak speed in a higher pressure range than is ordinarily possible with a conventional diffusion pump.

A further object of the invention is to provide a new vacuum pump operable in the high vacuum range and capable of working against a higher limiting forepressure than that causing forepressure breakdown with a conventional diffusion pump.

Another object of the invention is to provide a new pump combining both diffusion principles and ejector principles.

Another object of the invention is to provide a high vacuum pump wherein the pumping action of the diffusion jet nozzles is assisted by a positive pumping act-ion into the forepressure arm.

Another object of the invention is to provide a combined diffusion and ejector pump of improved construction whereby the various pumping elements coact in complementary and cooperating relation.

Another object of the invention is to provide a combined diffusion and ejector pump of improved design and capable of ready fabrication.

Other objects will be apparent from the drawings and from the description and claims which follow.

These and other objects are attained by means of this invention as described more fully hereinafter with particular reference to certain preferred embodiments as illustrated in the drawings.

in general, the vacuum pumps which embody this invention include three separate but interconnected chambars, namely, a vapor-generating chamber or boiler, a

primary pumping chamber corresponding generally to the pump casing on a conventional difiusion pump, and a secondary pumping chamber corresponding generally to the forepressure arm of a conventional difiusion pump. Unlike a conventional difiusion pump, however, the primary pumping chamber or pump casing is spaced above the boiler and communicates with the boiler by way of a vapor channeling rchimney opening out of the boiler and extending up inside the casing for a major part of the length of the :casing. Further, the forepressure arm which forms a secondary pumping chamber is spaced from the casing and the two pumping chambers are connected by a diifuser tube which opens laterally out of the casing below the upper end of the chimney and discharges into the forepressure arm at a point below the forepressure outlet port. The chimney is provided with a .jet nozzle assembly at its upper end, and this jet nozzle assembly is directed downwardly away from the inlet .port of the casing and toward the diltuser tube region. In addition, an rej'ector element opens out of the vapor chimney :below the jet nozzle assembly and is directed into'the mouth of the diffuser tube in the direction of the forepressure arm. The forepressure arm is provided with a trapped conduit for returning condensate to the primary pumping chamber where the condensate is combined with the condensed pump fluid from the primary pumping chamber. A second return conduit connects the pump casing to the boiler for returning the combined condensate to the boiler for revaporization.

The invention is 'best understood with particular reference to certain preferred embodiments thereof as illustrated by the drawings.

Of the drawings:

Fig. 1 is a view in elevation, partly broken away and in section, of a combined diiiusion and ejector pump constituting a preferred embodiment of the invention;

Fig. 2 is a section taken along line 22 of Fig. 1; and

Fig. 3 is a view in elevation, partly broken away and in section, illustrating a vacuum pump constituting an alternative embodiment of the invention and particularly adapted for large volume pumping.

With particular reference to Figs. 1 and 3, the vacuum pumps embodying the invention have a boiler 10 for vaporizing pump fluid, and, spaced above the boiler, an upwardly directed generally tubular pump casing 11. The boiler 10 and casing 11 are interconnected by 'a chimney 12 which opens out of the top of boiler 10 and extends upwardly into the casing 11 whereby pump fluid vapors are channeled from boiler 10 into casing 11. Chimney 12 projects inside casing 11 for a major part of the length of casing 11, with which it is concentric. The upper end of chimney 12 is capped by an umbrella jet cap 13 and the chimney 12 is provided with openings under the cap as shown at 14, to form a downwardly directed jet nozzle assembly. The upper end of casing fl above the jet nozzle assembly is open to form an inlet port 16 for the pump, the casing having a peripheral flange 17 around port 16 whereby the inlet port can be bolted or otherwise secured to the system to be evacuated.

An upwardly directed generally tubular forepressure arm 18 is spaced laterally from casing. 10, to which it is connected by a generally horizontal diffuser tube 19.. Diffuser tube 19 has its mouth opening out of casing 11 below the jet nozzle assembly and discharges into forepressure arm 18 belowthe outlet port 20 at the upper end of forepressure arm 18. Outlet port 20 is also pronot shown); the pump is further ensured by a staggered baflie plate fuser tube 19. Ejector element 23 is flared as it projects outwardly from chimney 12 and is arranged so as to discharge directly into the mouth of difiuser tube 19.

A coil 24 of copper tubing or other suitable material is wound around pump casing 11, forepressure arm 18 and diffuser tube 19 for carrying cooling water, coil 24 being provided with the usual inlet and outlet connections Condensation of pump fluid vapors in pump casing. A second condensate return conduit 29 connects pump casing 11 with boiler for returning the combined condensed pump fluid from the forepressure arm and from the pump casing to the boiler for revaporization.

Referring specifically to the pump illustrated in Fig. 1, in a preferred embodiment, boiler 10, which is fabricated of sheet metal or similar material, has a sidewall element 30 forming the sides and top of the boiler and a bottom plate 31 welded or otherwise secured to the sidewall 30 to serve as a bottom for the boiler. Sidewall 30 desirably extends below bottom plate 31 to form an annular skirt 32 which serves as a base for the pump and also encloses the resistance heater 33 which is bolted or otherwise secured to the lower face of bottom plate 30. Heater 33 includes the usual binding posts, one of which is shown at 34, for connecting the heater into an electrical circuit. A threaded drain plug 36 closes a drain opening through heater 33 and bottom plate 31 which permits draining of boiler 10.

Chimney 12, which is fabricated from metal tubing of the desired diameter, is welded into an opening in the top of boiler 10 so as to project upward vertically from the boiler. If desired, chimney 12 can be fabricated in sections which are joined together by an annular collar 37, particularly when it is desired to have a smaller di ameter to the chimney 12 above ejector element 23 whereby a portion of the pumping vapors escape more readily through ejector element 23.

Umbrella jet cap 13, which is press fitted onto the upper end of chimney 12, is flared to give optimum pumping action at the jet nozzle. The pumping efficiency is further enhanced by a double flared collar 38 mounted on chimney 12 with its outwardly flared upper end 39 under jet cap 13 opposite the flared portion of the jet cap. The lower end of collar 38, which is below the jet assembly, is flared out widely to form an annular skirt 40 which is arranged to deflect vapors emerging from the jet nozzle against the cooled casing 11.

In order to facilitate assembly and disassembly, casing 10 is desirably formed of a tubular sidewall 42 which is preferably of greater diameter in the region of the ejector element 23 than in the region of the jet nozzle assembly, and a bottom plate 43 which is secured in vacuum tight relation with sidewall 42 by means of bolts as shown at 44 and a rubber O-ring gasket 45.

Chimney 12 is insulated against undue heat loss in the space between boiler 10 and casing 11 by a concentric tubular envelope 46 which encircles chimney 12 and defines a dead air space around the chimney. Envelope 46 extends into casing 11 and supports the bottom plate 43 which is welded to envelope 46. The top 47 of envelope 46 is welded or otherwise secured to chimney 12 and the bottom of envelope 46 is welded to boiler wall 30. A small hole 48 inthe side of envelope 46 allows the pressure in the dead air space to equalize as the pump temperature changes.

In the embodiment illustrated in Fig. 1, the ejector element 23 and the diffuser tube 19 are each formed of a block of metal which has been bored to give the desired diverging and converging configuration to the vapor channel. As in the usual ejector-difiuser combinations, the channel in ejector element 23 is divergent from its intake to its discharge ends whereas diffuser tube 19 is convergent from its mouth, opening out of casing 11, down to a constricted throat 50 adjacent forepressure arm 18 and thence divergent at its discharge end opening into the forepressure arm.

The battle plate assembly 25 which has been found to be particularly effective in preventing loss of pump fluid out through outlet port 20 consists of a stacked arrangement of generally semicircular plates 51, 51 mounted in staggered relation on a tie rod 52 which is mounted inside and extends up through the center of forepressure arm 18.

Condensate return conduit 26, connecting forepressure arm 18 with casing 11, is secured to the bottom of forepressure arm 18 by means of a threaded nipple 53 which projects into the arm for a short distance above the bottom of the forepressure arm so that any foreign solids entrained in the condensed pump fluid can settle out and not enter conduit 26. A similar threaded nipple 54 con nects the other end of conduit 26 into a tapped hole in the lower margin of the sidewall element 42 of casing 11.

The second condensate return conduit 29, connecting casing 11 with boiler 10, opens into casing 11 through bottom plate 43 to which it is connected by a suitable fitting 56. Conduit 29 is provided with a trap 57 adjacent the discharge end of the conduit, and a removable plug 58 permits ready access into trap 57 for cleaning or the like. The discharge end of conduit 29 is welded to boiler 10 and opens into the boiler below the normal level of liquid in the boiler.

A construction particularly adapted for large pumps is illustrated by Fig. 3 of the drawings. In this alternative embodiment, a barrel-like boiler 10 is employed, and an immersion heater 60 is used directly in the pump fluid. Installation and removal of heater 60 is facilitated by mounting it on a removable end wall 61 which is bolted into position on boiler 10. The boiler 10 and chimney 12 are insulated against heat loss by a layer of suitable lagging material 62, and the entrainment of liquid droplets in the vapor stream entering chimney 12 is obviated by a baffle plate 63 mounted inside boiler 10 and shielding the mouth of chimney 12.

Because of the size of the component parts, chimney 12 is constructed in distinct sections which nest together as indicated at 64, and the various nested elements are held in place by a transverse rod 65 removably mounted on top of jet cap 13 and locked under lugs 66, 66 on the wall of casing 11. p

In order to facilitate cooling of the large volume of vapors issuing from the jet nozzle, an internal cooling coil 67 is mounted under flared skirt 40 below the jet nozzle, coil 67 having inlet and outlet ends (not shown) emerging through casing 11 and being provided with conventional external water supply and drain fittings. Diffuser tube 19, in this embodiment is fabricated from sheet metal, rather than a block of metal, to reduce weight and facilitate cooling of the tube. Similarly, ejector element 23 is made of sheet metal and is constructed in two parts. A piece of straight tubing 69 welded into chimney 12 forms the inlet of ejector 23 and a flared mouth portion 70 is secured thereto by means of a screw coupling 71.

In operating the apparatus illustrated by the drawings, the inlet port is connected to the system to be evacuated and the outlet port is connected to a backing pump. The heater vaporizes pump fluid in the boiler and the vapors pass upwardly through the chimney into the pump casing. A portion of the vapor stream is diverted out of the chimney through the ejector element and the complementary diffuser tube so as to pump against the pressure in the forepressure arm.

The remainder of the vapor stream ascends the chimney and is emitted in a downwardly directed accelerated stream from the jet assembly, thereby pumping gases in through the inlet port from the system being evacuated. The vapors emerging from the jet nozzle are condensed in large measure by contact with the flared skirt and the cooled casing wall and the condensate flows downwardly to the bottom of the casing. Uncondensed vapors and the gases being pumped are swept into the mouth of the diffuser tube and assist in the pumping action. Vapors condensing in the diffuser tube before reaching the constricted throat flow back into the casing. Vapors emerging from the diffuser tube into the forepressure arm are deflected back and forth by the bafile plate assembly and are condensed on the cooled wall of the forepressure arm. The non-condensable gases pumped in through the inlet port are swept along and leave the pump through the outlet port in the forepressure arm where they are pumped out of the system by the backing pump.

The condensed pump fluid from the forepressure arm flows to the bottom of the secondary pumping chamber within the forepressure arm and is returned to the pump casing by flowing through the condensate return conduit. The combined condensate from the two pumping chambers then is returned to the boiler for revaporization by flowing downwardly through the second return conduit connecting the casing with the boiler.

Thus by means of this invention, all of the pump fluid vapors are utilized in the pumping action. The ejectordiifuser combination works against a higher limiting forepressure than would be possible with the jet nozzle alone, and assists the jet nozzle in maintaining peak pumping speeds in a higher pressure range than is possible with a conventional diffusion pump. The forepressure arm is utilized as a secondary pumping chamber rather than merely as a vapor trap. The ejector-difiuser and the jet nozzle work off a single vapor stream and hence coact in a highly eifective fashion to give optimum performance. The pump approaches a diffusion pump in compactness, and is readily assembled, disassembled and cleaned.

Although the invention has been described in considerable detail with reference to certain preferred embodiments, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as illustrated by the drawings and described hereinabove and as defined in the appended claims.

I claim:

1. A multi-stage vacuum pump comprising an upright casing, a boiler connected to the lower end of the casing, a vapor chimney extending upwardly in the casing from the boiler, jetting means connected to an upper portion of the vapor chimney and disposed inside the casing, an ejector element having an inner end opening into the vapor chimney and disposed at the side thereof in the casing between the boiler and the jetting means, a difiuser tube connected to and projecting through the side of the casing adjacent the ejector element, an outer end of the ejector element opening into the diffuser tube, a gas inlet connected to the casing above the jetting means and a gas outlet connected to the diifuser tube outside the casing.

2. A multi-stage vacuum pump comprising an upright casing, a boiler connected to the lower end of the casing, a vapor chimney extending upwardly in the casing from the boiler, jetting means connected to an upper portion of the vapor chimney and disposed inside the casing, an ejector element having an inner end opening into the vapor chimney and disposed at the side thereof in the casing between the boiler and the jetting means, the portion of the casing around the ejector element being of enlarged cross section, a diffuser tube connected to and projecting through the side of the casing adjacent the ejector element, an outer end of the ejector element opening into the diffuser tube, a gas inlet connected to the casing above the jetting means and a gas outlet connected to the diffuser tube outside the casing.

References Cited in the file of this patent UNITED STATES PATENTS 1,465,030 Unglaube Aug. 14, 1923 1,664,398 B01 Apr. 3, 1928 2,291,054 Nelson July 28, 1942 2,366,277 Madine Jan. 2, 1945 2,386,298 Downing Oct. 9, 1945 2,386,299 Downing Oct. 9, 1945 2,696,344 Power Dec. 7, 1954

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