US2608343A

US2608343A - Vacuum pump

Info

Publication number: US2608343A
Application number: US95938A
Authority: US
Inventors: August P Colaiaco; Dwight L Hopper
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1949-05-28
Filing date: 1949-05-28
Publication date: 1952-08-26
Anticipated expiration: 1969-08-26

Description

g- 26, 1952 A. P. COLAIACO arm. 2,608,343

VACUUM PUMP Filed May 28, 1949 T (D N N ll" I |0- we? a I I 9 2 H llll 111% 2 2' w I N N WITNESSES: INVENTORS 6 August RColoiuco and Dwight L.Hopper.

BYJ ,4. $5M

ATTORNEY Patented Aug. 26, 1952 VACUUM PUMr August P. Colaiaco, Pittsburgh, Pa., and Dwight L. Hopper, Jacksonville, Ill;, assignorsto Westinghouse Electric Corporation, East Pittsburgh, Pa.,acorporation ofPennsylvania sp nt-tummy 28, 1949; ea No. 95,933

Our invention relates to a vacuum pump, and

particularly to an oil diffusion pump having high pumping speeds against high back pressure.

In conventional designs of vapor pumps, high speed has been obtained by having a first stage with a large pumping radius (the pumping radius beingthe. distance between the edge of the first stage jet-and the inside Wall of the pump barrel) and decreasing the pumping radius of each successive stage to produce a decrease of pumping radii from the intake to the exhaust end of the pump. Heretoforc, this "decrease of pumping radii has been obtained by using a substantially uniform diameter pump barrel and increasing the diameter of the pumping stages from the first through the pumping vapor is of material quantity. Consequently, these high speed pumps will not exhaust against a high back pressure and it is accordingly customary to use a booster pump to increase the exhaust pressure so that a secondary or mechanical vacuum pump will be eflicient in discharging the pumped gases. i

According to our invention; we have provided a diffusion pump havinghigh pumping speeds and capable of exhausting against high back pressures, so that a booster pump may be dispensed with.

In a construction according to our invention, each of the pumping jets or stages is of substantially uniform diameter and the pump barrel is substantially irustroconical converging from a large intake opening to a relatively small exhaust opening. By this manner, the large pumping radii of the first stage is obtained and the small pumping radii of the last stage is obtained, but with the additional advantage that the cross sectional area of the exhaust stage is relatively small, so that almost no back streaming results and the pump therefore will operate against the high back pressures normal for booster pumps.

It is possible and practical to fit a small spinning into a small opening with much smaller tolerances than are required when fitting large spinnings into large openings. Consequently, in a pump according to our construction, the pumping radii and the exhaust area can be made much smaller and precise than in the heretofore conventional type pumps.

In the conventional pumps having a plurality of pumping jets fed from a single vapor chimney, starvation of the jets farthest removed from the 1 Claim. (Cl. 230-101) source of vapor has frequently been "observed. Thisstarvation results primarily from the-ex haustion of the gas by its being utilized by the jets nearest the source of vapor or by cooling which reduces the volume of the vapor. We have found that by introducing the'vapor fromthe pump intermediate. the jets, th vapor reaches "all of the jets at substantially the same pressuregthus materially increasing the effectiveness of the pump. When it is desired to distribute the pres-f sure in some particular order the vapor inlet may be shifted to introduce the vapor at or near the point where the highest pumping pressure is desired. i In order toprovide a" relatively short distance from the boiler or other source of vapor to the pumping chimney, we provide a horizontal pump with a boiler attached adjacentthe mid portion of the pump, so that a relatively short vapor passage connects. the boiler to an intermediate portion of the chimney. I

- It isaccordingly' an object of our invention to provide a high speed, high pressure vacuum pump.

It is a further object. of our invention to pro vide a vacuum pump in which the pumping area decreases Irom the intake the pump.- v f r a 1- It is a further1 object of our invention to provide a. vapor. pump having substantially. uniform or controlled vapor pressures to all pumpingjets.

Other objects and advantages of our invention will be apparent from the following detailed description taken in conjunction With the accompanying drawing, in hich the figure is a sectional elevation of a vapor condensation pump according to our invention.

In the exemplary embodiment of our invention, a vapor diffusion pump comprises a substantially frustroconical body or barrel portion 10 having cooling coils H applied to the exterior surface thereof so that the interior surface l2 of the barrel I0 is a cooling surface for the pumping vapors. Substantially axially arranged in the pumping barrel is a chimney or supply pipe IE on which is arranged a plurality of pumping jets l6. Preferably, these jets l6 are substantially uniform in diameter, so that each of the spinnings, except the initial stage Hi, can be identical spinnings.

Usually it is preferred to provide the initial spinning it in the form of a cap I'l substantially closing the initial end of the vapor chimney 15, but obviously the first stage Hi can be exactly like all of the other stages and the cap either to the exhaust end of 3 dispensed with or provided as a portion of the chimney 5. The larger intake end l8 of the pumpfibarrel H1 is connected to the space |9 to be evacuated and the smaller or exhaust end 20 of the barrel H) is connected to any sort of secondary vacuum pump.

A boiler 2| is attached to the pump adjacent the central portion thereof and has a vapor tube 22 extending from the boiler 2| to a junction 23 with the chimney l substantially adjacent the mid portion thereof or at least intermediate the ends of the chimney I5 and. between the pumping stages Hi.

In order to prevent cooling of the vapor between the boiler 2| and the pumping chimney I5, a plurality of concentric tubes or shields 24 and 25 are placed around the vapor passage 22 and are open to the interior of the pump, so that a, low pressure will be maintained in the space between the concentric tubes 24-25 and the vapor passage 22. Preferably the portions of the chimney |5' are mounted on and supported by the vapor tube 22 so that different types of pumps may be constructed by simply screwing in portions of the chimney |5 having the desired pumping jets Hi. In order to return condensed pumping material to the boiler 2|, a return pipe 26' is provided from adjacent the large end It! of the barrel Hi to a point adjacent the bottom of the boiler 2|. Usually some sort of barrier 27 is provided to prevent condensed pumping fluid passing the inlet port of the return tube.

While any sort of heating device may be utilized for the boiler, we prefer to provide an electric heater 28 either immersed in the oil or attached in good thermal relation to the external portion of the boiler 2|. Any suitable thermal insulation, not shown, may be applied to the boiler 2| or the exposed portion of the heat conserving concentric tubes 24.

In the operation of the pump according to our invention, the large end I8 is attached to the space I9 to be evacuated and the exhaust end 20 to any suitable vacuum pump and heat is applied to the boiler 2| to produce a flow of vapor into the chimney |5 and from the chimney l5 through the pumping jets IS. The pumping vapor entrains molecules of gas and causes them to move from the intake to the exhaust end of the pump so that a very low pressure will be maintained at the intake and a higherpress'ure at the exhaust end of the device.

' of our invention and described the same to the best of our present ability, we wish it to be understood that changes and modifications can be made therein without departing from the true spirit. of our invention or the scope of the appended claim.

We claim as our invention:

A vapor pump comprising means for providing a tapering chamber, cooling means applied to said chamber to produce a condensing surface therein, a vapor supply pipe of substantially uniform diameter from end to end, located substantially centrally within said chamber, said supply pipe having an end-structure at each end, a plurality of difiusion jets of substantially uniform diameter connected to said vapor supply pipe at spaced points along its length, said jets being directed to move gas from the large to the small end of said chamber, a boiler for producing pumping vapor, and connection-means for sup plying vapor from said boiler to said vapor supply pipe, said connection-means being at a point intermediate the ends of the vapor supply .pipe.

. AUGUST P. COLAIACO. DWIGHT L.'HOPPER.

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

' I UNITED STATES PATENTS Number Name Date 2,237,806 Bancroft Apr. 8, 1941 2,390,814 Stallman Dec. 11, 1945 2,447,636 Colaiaco Aug. 24, 1948 FOREIGN PATENTS Number, Country Date 75,901 Sweden Mar. 26, 1931