US2931561A - Vacuum pumps - Google Patents

Description

April 5, 1960 U HlEslNGl-:R 2,931,561

VACUUM PUMPS Filed Nov. 7, 1956 2 Sheets-Sheet 1 aa Y 3a L/6 INVENTOR.

LEOPOLD H/Es/NGER l BY 1 m,MM

ATTORNEYS April 5, 1960 LJHIESINGER 2,931,551 VACUUM PUMPS v Filed Nov. 7, 195e 2 Vsheets-sheet a `l LEOPOLD H/ES/NGER A T TURA/E KS United' States Patent O vAcUUM PUMPS Leopold Hiesinger, Wachenbuchen Kreis Hanau, Germany, assignor to W. C. Heraeus, G.m.b.H., Hanau, Germany This invention relates to vacuum pumps, land more particularly to vapor-operated vacuum pumps.

In the well-known ejector and condensation type vapori operated pumps, a suitable uid, such as mercury or an organic oil with low vaporpressure, is used as a pumping medium. The uid is vaporized in a boiler'and conducted through a conduit or chimney to a nozzle within a pump casing which has an inlet connected: to a system to be evacuated and an outlet connected to a backing pump, usually a mechanical rotary oil sealed pump.

The vapor leaves the nozzle in the form of an annular jet and carries gas with it from the pump inlet toward the pump outlet. The pumping vapor is condensed and returned to the boiler for further use, and the pumped gases are forced out of the pump outlet by the additional ow of pumping vapor. In the ejector type pumps, the vapor leaves a nozzle at a supersonic velocity and pumps gases at very low pressures and at high pumping speeds. However, the elfectiveness of a Vapor-operated pump depends on the speed of the pumping vapor molecules, the number of molecules leaving the nozzle, andthe back pressure provided by the backing pump.

As a general rule, the pressure at the vapor operated pump outlet cannot be much more than about half the ypressure of the vaporized pumping fluid just before it f leaves the nozzle.

complished by heating the pumping uid as much as possible. However, thermal decomposition ofthe pumping uid sets an upper limit on the amount of heat which can be supplied to it. This invention provides a means for increasing the amount and pressure of the vaporized iiuidv supplied to the nozzle of a vapor operated pump without an attendant increase in heat input to the pumping fluid.

Briefly, the invention provides a vapor operated pump which includes a casing having an inlet and an outlet. A boiler is connected to the casing and adapted to contain a pool of liquid. A vapor conduit is disposed within the casing and connected to the boiler. Means are provided for vaporizing the liquid in the boiler, and a nozzle is connected to the conduit and opens into the casing to direct vapor from the casing inlet to the outlet. Mechanical pumping means are provided in the conduit between the boiler and the nozzle for increasing the pressure and amount of vapor flowing through the nozzle.

The mechanical pumping means in the conduit not only increases the pressure of the vapor being delivered to the nozzle, but it also decreases the pressure on the boiler, permitting more pump fluid to be vaporized at a lower pressure than with conventional vapor-operatedl pumps. This results in a correspondingly small decomposition of the pumping uid.

Any suitable mechanical pumping means may be used,

but I have'found that Roots type pumps are particularly suitable, because, when properly designed, they operate very effectively in the low pressure range prevailing in the boiler of typical vapor operated pumps. Moreover, Roots pumps are able to maintain a high compression ratio, for example, 10 to l and even higher.

These and other aspects of the invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:

Fig. l is a schematic sectional elevation of an embodiment of the invention in a single stage vapor-operated pump; and

Fig. 2 is an embodiment of the invention in a three stage vapor-operated pump.

Referring to Fig. l, a Roots type mechanical pump 10 has an inlet 12 connected to the upper end of a frustoconical boiler 14 which has a heating coil 16 in its bot tom. A pool 17 of pumping fluid, say an organic oil, is in the bottom of the boiler. An outlet 18 of the Roots pump is connected to the lower end of an upright frus'toconical chimney or conduit 19 which is coaxially disposed within a vertical cylindrical casing 20 having an inlet 21 at its upper end which is adapted to be connected by an outwardly extending flange 22 to a system (not shown) to be evacuated. The lower end of the casing is connected to the upper portion of the pump around the pumpoutlet. An annular nozzle 24 on the upper end of the vapor conduit is adapted to direct a jet of pumping vapor downwardly away from the casing inlet toward a casing outlet 2'5 at the lower end of the casing. The casing outlet is connected by a conduit 26 to a sepa- Irator 27 which has an outlet 28 adapted to be connected to a mechanical backing pump (not shown). The pump casing andseparator have external cooling coils 30, which are supplied a cooling liquid, such as water, to condense the vaporized pumping fluid.

Condensed vpumping uid flows to the bottom of the separator, where it flows through a condensate return line 32 back to the boiler. Baffles 34 are supported by spiders 36 in the separator over the separator outlet and condensate return.

The Roots pump has a pair of Roots type impellers 38 which are each mounted on a respective shaft 39 adapted to be turned by a suitable electrical motor (not shown).

In the operation of the pump of Fig. 1, the backing pump is turned on to reduce the pressure within the vapor operated pump to a suitable value, and then the heating element and the Roots pump are turned on. The Roots pump reduces the pressure over the pool of liquid inthe boiler, permitting the pumped liquid to boil at a relatively low temperature, and at the same time, the Roots pump delivers a large quantity of high pressure pumping vapor to the nozzle. The vapor from the nozzle streams downwardly toward the casing outlet, carrying pumped gases with it. The pumping vapor is condensed on the casing walls and in the separator, where it is separated from the pumped gases, which pass on to the backing pump. 'The condensed pumping fluid re turns through the condensate through the boiler for reuse.

Referring to Fig. 2, a three-stage vapor-operated pump 42 includes a vertical cylindrical casing 44 having an inlet 46 at its upper end and an outlet 47 at its side just above its bottom. The casing inlet is adapted to be connected by an outwardly extending ange 48 to a systemV ,into the cooling jacket through a lower conduit 53 and leaves through an upper conduit 54.

The lower end of the casing is closed by a bottom 56 and serves as a boiler 57 which contains aV pool 58 of pumping iluid. An inner chimney or vapor conduit 60 includes a lower frusto-conical section 61 which has its lower end disposed in the pool of pumping iluid, and its upper end connected to an inlet 62 of a Roots type vacuum pump 64 which has a pair of Roots type impellers 65 mounted on rotatable shafts 66. The outlet 68 of the Roots pump'is connected to a vertical and cylindrical upper section 70 of the inner vapor conduit. The upper end of the upper section terminates in an annular central nozzle 72 adapted to direct an annular jet of pumping vapor downwardly away from the casing inlet toward the casing outlet.

An intermediate vapor conduit 74 is formed between a pair of annular and concentric inner and intermediate tubes 75 and 76, respectively, which have ytheir lower ends disposed in the pumping fluid in the boiler, and which have formed at their upper ends an annular intermediate nozzle 77 located below the central nozzle and adapted to direct pumping vapor toward the casing outlet. An outer vapor conduit 78 is formed between intermediate tube 76 and an outer tube 79. The upper portion of tube 79 is frusto-conicaled and terminates in an annular outer nozzle 80 which is located below the intermediate nozzle and directs pumped vapor toward the casing outlet. An upper frusto-conical shield 82 is attached at its upper end to the inner vapor conduit just below the central nozzle. The lower end of the upper shield is connected to the top of the intermediate nozzle. A lower frusto-conical shield 84 is connected at its upper end to intermediate tube 76 just below the intermediate nozzle. A cooling coil 86 is disposed in the central portion of the boiler, and a heating coil 88 is disposed in the boiler coaxially around the cooling coil.

The shafts are driven by an electrical motorV (not shown) which is supplied electrical power through leads (not shown) sealed through the casing wall and shield 82 in a vacuum tight manner. v

The operation of the apparatus of Fig. 2 is similar to the operation of the apparatus of Fig. 1. .The backing pump is turned on to reduce the pressure in the vapor operated pump toA a low operating value, and then the heating coil and Roots pump are turned on. Vapor ows up each of the vapor conduits, the Roots pump increasing the pressure of the vapor supplied to the inner nozzle, and decreasing the pressure of the vapor over the portion of the boiler within the inner vapor conduit. The vapor leaving the nozzles entrains gas to be pumped and is then condensed on the casing walls where it flows down the casing interior to the annular space between the outer tube 79 and the casing. The condensed uid then ows inwardly over the heaters where it is re-heated for boiling. For the inner or high vacuum nozzle, it is important that there be as little readily volatile pumping fluid resulting from thermal decomposition as possible. To achieve this eiect, a cooling medium such as water, is circulated throughthe cooling coils in the central portion of the boiler. In addition to the cooling effect of the cooling coil, the reduced pressure created over the central portion of the pool of pumping fluid decreases the boiling temperature of the fluid and insures operation below the thermal decomposition temperature.

With multi-stage pumps, such as the type shown in Fig. 2, it is possible to provide any of the vapor conduits, and as many of them as is desired, with mechanical vapor pumping means, such as is shown for the inner vapor conduit. Y

I claim:

l. A vapor-operated pump comprising a casing having an inlet and an outlet, a boiler connected to the casing and adapted to contain a pool of liquid, a conduit disposed within the casing and in communication with the boiler, heating means associated with the boiler for vaporizing the liquid in the boiler, a nozzle connected to the conduit and opening into the casing to direct vapor away from the casing inlet toward the outlet, and mechanical pumping means positioned in the conduit between the boiler and the nozzle for increasing the pressure of the vapor owing through the'nozzle. 2. A vapor-operated pump comprising a casing having an inlet and an outlet, boiler means connected to the casing for vaporizingka liquid charge in the boiler means, a conduit disposed within ,the casing and in communication with theboiler, a nozzle connected to the conduit and opening into the casing, the nozzle directing vapor from the boiler means and passed by the conduit away from the casing inlet toward the outlet, andy mechanical pumping means in the conduit between the boiler and the nozzle for increasing the pressure of the vapor Howing through the nozzle. I

3. A vapor-operated pump comprising a casing having an inlet and an outlet, boiler means for heating and vaporizing a liquid charge, a conduit disposed within the casing, a nozzle connected to the conduit and opening into the casing to direct vapor away from the casing inlet toward the outlet, and a mechanical pump having an inlet connected to the boiler and an outlet connected to the conduit for decreasing the pressure in the boiler and increasing the pressure of the vapor flowing through the nozzle.

4. Apparatus according to claim 3 in which the mechanical pump is a Roots type pump.

5. A multistage vapor-operated vacuum pump comprising a casing having an inlet and an outlet, a boiler connected to the casing and adapted to contain a pool of liquid, a plurality of conduits disposed within the casing and each in communication with the boiler, means associated with the boilervfor heating and vaporizing the liquid in the boiler, a nozzle connected to each conduit and `.opening into the casing to direct vapor from the casing inlet to the outlet, and mechanical pumping means in atleast one of the conduits between the boiler and the nozzle connected to the said one conduit for increasing the pressure of the vapor owing through the nozzle.

References Cited in the le oi this patent UNITED STATES PATENTS 118,472 Munzinger Aug. 29, 1871 550,628 Lester a Dec. 3, 1895 1,013,499 Kunzli Jan. 2, 1912 1,082,113 Diden Dec. 23, l9l3 2.639,086 Dayton za.. May 19, 1953

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