US2432226A - High-speed high-pressure vacuum pump - Google Patents

Description

WM. J. H. cox ET AL v432,22

HIGH-SPEED HIGH-PRESSURE VACUUM PUMP Filed April 30, 1945 WITNESSES. INVENTORS Jose h H. Cox, Dwi ht LHoppw' W MVQIJML JLJ fluyugt P [0 az'aco.

Patented Dec. 9, 1947 HIGH- SPEED HIGH-PRESSURE VACUUM PUMP Joseph H. Pittsburgh, Dwight L. Hopper,

Wilkinsburg, and August P. Colaiaco, Pittsburgh, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 30, 1945, Serial No. 591,080

3 Claims. 1

Our invention relates to a high-speed, highpressure oil diffusion vacuum pump, and particularly to an oil diffusion pump capable of operating at high speeds against a high back pressure. a

In the utilization of vacuum systems, it is frequently desirable to rapidly evacuate relatively large capacities. The vacuum system for doing this comprises a high vacuum pump, such as an oil diffusion pump and a secondary or backing pump usually of'the oil sealed rotary variety.

As heretofore constructed, the oil diffusion pumps have been able to handle large quantities of gas only when pumping at a very low back pressure ofthe order of 150 microns. However, to effectively handle large volumes of air, the oil sealed mechanical pump should have a relatively large fore pressure, such as the order of 500 to 1000 microns.

Referring to our invention, we have provided an oil diffusion pump which will deliver large quantities of gas at a back pressure of the order of 500 to 1000 microns and still produce the desired high vacuum, thus meeting the needs of the backing pump and producing a high speed pumping combination.

In order to produce this type of pump, we have provided a boiler having a large oil vapor evolving surface and provided the boiler with enlarged heat conducting surfaces so that large quantities of heat may be conducted into the boiler at low temperature levels and without causing local hot spots violent boiling or turbulence in the boiler.

The vapor evolved from the boiler is maintained in a high head pressure chamber and is conducted to a chimney connected to a substantially axially directed pumping jet which acts not only to entrain gases by the jet action, but also is enclosed in a cooled condensing chamber to act in a normal manner of a condensing pump. In order to prevent reverse vapor flow in the jet chamber, a vapor chimney is secured in gas tight relation, preferably by means of a suitable packing between the bottom of the chimney and the top of the pressure chamber.

The condensing chamber is connected to a cooled return conductor extending below the oil surface in the boiler, so that the oil acts as a seal to prevent vapor returning to the jet chamber through the oil returned.

It is accordingly an object of our invention to provide an oil diffusion pump operable against a high back pressure.

It is a further object of our invention to provide an oil diffusion pump having high-speed,

high-pressure characteristics.

It is a further object of our invention to provide an oil diffusion boiler having low heat levels with high heat transfer.

It is a further object of our invention t provide an oil diffusion pump which eliminates back streaming in a pumping chamber.

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

In the exemplary embodiment of our invention, the high-pressure, high-speed pump comprises an oil boiler I0 having a relatively large vapor evolving surface I I to produce large volumes of oil vapor at high head and to which is connected a pressure chamber I2 preferably of considerably less diameter than the diameter of the boiler I0, and of sufiicient height to support a column of oil l3 equal to the head produced by the boiler,

In order to prevent destructive distillation of r the oil in the boiler Ill, an external heater I4 is applied to a portion I5 of the boiler wall and a plurality of bafiies l6 which may be of any desired configuration are connected to the heated portion I5 of the container and extend into the oil to provide a. large heat transferring surface, so that large quantities of heat may be transferred a relatively low levels of temperature and without causing excessive boiling or turbulence of the oil.

The external portions of the boiler l0 and the pressure chamber I2 are covered with heat insulating lagging II to prevent excessive losses of heat from the boiler surfaces.

A vapor chimney 20 is connected to the pressure chamber I2 and in order to prevent back streaming or leakage around the chimney 20, a packing 2| is provided, preferably in a groove 22 at the bottom of the chimney 20, and means such as a bolt 23 is provided for drawing the chimney 20 into gas tight relation with the packing material 2 I.

The chimney 20 terminates in a pumping jet 30 herein illustrated as of the axially directed variety which by jet action helps to entrain gas molecules entering through the connection 29.

The jet 30 is enclosed in a condensing chamber 3|, the walls. 32 of which are cooled by suitable means such as cooling coils 33 applied preferably to the external surface thereof.

In order to prevent revaporization of oil flowing about the base of the chimney 20 the cooling 3 coils 83 are extended adjacent to the groove 22, and the plate containing groove 22 as well as the unprotected part of the pressure column is protected by a baflle 25 secured in spaced relation to the inner side of the pressure column and extending adjacent the groove. An oil return 34 is provided and so connected to the condensing chamber 3! that any oil collecting in the chamber 3! immediately flows into the oil return 34 and does not provide stagnant pools which might absorb heat and thereby revaporize. The oil return 34 is external to the pressure chamber l2 to'prevent leakage of heat into the returning oil and extends to a point adjacent the bottom of the boiler In so that the oil l3 in the return connection 34 provides a vapor seal between the boiler l and the condensing chamber 31 and thus prevents back streaming through the 011 return 34.

In the operation of our pump heat is applied to the boiler to produce vapor at a high head and delivered through the axially directed jet 30 to draw gas through the intake 29 and deliver the same through the outlet 35 to a mechanical pump (not shown). Because of the pressure and direction of the vapor in the jet the pump will deliver gas against a back pressure of the order of 1000 microns even when the pressure of ,the inlet approaches a pressure of zero.

The ability to operate against a high back pressure enables the mechanical pump to operate with a high fore pressure thus producing a high speed evacuation of any chamber connected to inlet 29.

While for purpose of description we have shown and described a specific embodiment of our invention, it will be apparent that changes and modifications can be made therein without departing from the true spirit of our invention and by the scope of the appended claims.

We claim as our invention:

1. A- vacuum pump comprising a boiler of large surface area, an external heater applied to said boiler, bailies in said boiler and in contact with the heated exterior surface to increase the heat conducting area, a pressure chamber of less diameter than said boiler, a vapor chimney connected to said pressure chamber, a vapor jet supplied by said chimney, a condensing chamber about said jet and a condensate return from said condensing chamber to a point below the surface of the liquid in the boiler, said return being so connected that all condensate rapidly drains from the condensating chamber, a vapor seal between said boiler and said chimney and means for cooling said vapor seal.

2. A high pressure vacuum pump comprising a boiler chamber, a heater therefor, means for distributing the heat uniformly throughout said boiler, a vapor chamber connected to said-boiler,

, a vapor jet fed from said boiler, and cooling means to prevent back streaming of vapor about said let.

3. An oil diiTusion vacuum pump comprising a boiler having a large vapor evolving area, heating means for said boiler, means for preventing local excess temperature in said boiler, a vapor jet fed by said boiler, a condensing chamber about said jet, a condensate return from said chamber to a point adjacent the bottom of said boiler, and cooling means for preventing revaporization of condensate in said condensing chamber.

JOSEPH H. COX. DWIGHT L. HOPPER. AUGUST P. COLAIACO.

REFERENCES CITED The following references are of record in the

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