US2933233A

US2933233A - Vacuum pumps

Info

Publication number: US2933233A
Application number: US502776A
Authority: US
Inventors: Gordon P Gerow; Raymond J Weeks
Original assignee: Consolidated Electrodynamics Corp
Current assignee: Consolidated Electrodynamics Corp
Priority date: 1955-04-21
Filing date: 1955-04-21
Publication date: 1960-04-19
Anticipated expiration: 1977-04-19

Description

April 19, 1960 P. GEROW ET AL VACUUM PUMPS 2 Sheets-Sheet 1 Filed April 21, 1955 PUMP ---- MECHANICAL 0 7 villi!!! all!!! will! w T mu V NP N w m G III I. id

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RAYMOND J. WEEKS m m gw ATTORNEYS IS a To. WORK 1 2,933,233 VACUUM PUMPS Gordon P. Gerow and Raymond J. Weeks, Rochester,

N.Y., assignors, by mesne assignments, to Consolidated Electrodynamics Corporation, Pasadena, Calif., a corporation of California Application April 21, 1955, Serial No. 502,776 9 Claims. (Cl. 230-101) This invention relates to vapor-operated vacuum pumps.

The usual vapor-operated vacuum pump comprises an upright pump casing having an inlet at its upper end adapted to be connected to a piece of work to be evacuated. An outlet or discharge is provided in the pump casing at a point spaced from the inlet, and the bottom of the pump casing is closed to form a pot or boiler for containing a pool of liquid to be vaporized. A conduit or chimney extends upwardly within the casing from the boiler and delivers vaporized liquid to a jet or a plurality of jets positioned coaxially within the casing. The jets are arranged to direct vapor away from the pump inlet and toward the outlet so that the vapor streaming from the jets entrains gas molecules diffusing from the work and forces the gas toward the pump outlet where it is carried away by a mechanical or backing pump. The vapor-operated pumps do not exert an eificient pumping action except at relatively low pressures, say less than one millimeter of mercury, and a backing pump is necessary to produce the required low pressure before the vapor-operated pump can perform effectively.

One of the disadvantages of vapor-operated pumps is that the liquid or pumping fluid is usually an Organic material which is readily oxidized or otherwise deteriorated when exposed to the atmosphere at the temperature required for operation. For this reason, precautions must be taken to avoid exposing hot pump fluid to air at pressures substantially higher than the operating pressure of the pump if damage to the pumping fluid is to be avoided.

In some uses of a vapor-operated pump it is necessary to cycle the pump, that is, cyclically connect the pump to a piece of work to be evacuated, reduce the pressure within the pump and work to the operating range of the pump, heat the pump fluid to put the pump into operation, evacuate the work to the required low pressure, tip off or otherwise seal the work, reduce the temperature of the pump fluid to a safe value, admit atmospheric pressure into the pump, and then connect another piece of work to the pump and repeat the cycle. Sometimes valves are used to isolate the pump from atmospheric pressure when the work is removed to avoid the necessity of cooling the pump fluid and exposing it to atmospheric pressure each cycle. However, many operators find that the use of valves incurs operational failures of the valves which often result in the loss of valuable pump fluid and loss of operating time for the pump. Therefore, these operators prefer to use valveless systems and take the precaution of cooling the pump fluid from its operating temperature to a certain prede termined safe temperature before exposure to atmosphere.

One method for achieving this reduction in pump fluid temperature is simply to turn off the boiler heating element and wait for the pump fluid to cool to a safe value. Another method is to provide cooling coils around the exterior of the pump casing in the vicinity of the boiler. When the pump fluid is to be cooled a cooling fluid such as tap water is circulated through the external coil to cool the pump fluid to a safe value. Both of these two cooling methods have the disadvantage that a prolonged cooling period is required to reduce the temperature of the liquid to a safe value. Moreover,

States Patent these methods cool the entire body of pump fluid and increase the time required for re-heating the pump fluid to its operating temperature. These methods of cooling are therefore time-consuming and ineflicient.

This invention provides a vapor-operated pump in which the pump fluid is cooled rapidly by internal cooling means, and preferably, the cooling means are arranged to cool only the upper portion of the pool of pump fluid which is the only part exposed to the atmosphere. Thus, with the cooling means of this invention the pump fluid is cooled rapidly, and preferably only a portion of the fluid is cooled so that it may be quickly re-heated for cyclical operations. This provides a vapor-operated pump with an extremely short cycle time.

Briefly, the invention contemplates a vapor-operated pump comprising a pot for containing a pool of liquid to be vaporized, and means for heating the pool of liquid. A jet through which the resulting vapor is discharged is connected to the pool by a vapor chimney, and a conduit is disposed Within the pump for introducing fluid into the pump from the pump exterior.

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

Fig. 1 is a vertical section of a vapor-operated pump showing the use of an internal coil in the boiler in accordance with this invention;

Fig. 2 is a view taken on line 2-2 of Fig. 1;

Fig. 3 is a graphic comparison of the cycle time of a pump using an internal cooling means in accordance with this invention with the cycle time of an identical pump not using the cooling means of this invention; and

Fig. 4 is a vertical section of the lower end of the pump casing in which the cooling coil is disposed above the normal operating level of the pump fluid.

Referring to Figs. 1 and 2, a typical vapor-operated pump 10 comprises an upright cylindrical pump casing 12 with its upper end open to form a pump inlet 13 provided with an outwardly turned flange 14 for connecting the pump inlet to a piece of work (not shown). An outlet conduit '15 is connected to the side of the casing slightly more than half-way down the length of the easing. A first section 16 of the outlet conduit slopes upwardly away from the casing and joins the lower end of a vertical section 17 of the outlet conduit which in turn is connected at its upper end to a horizontal section 18 of the outlet conduit having an outwardly turned flange on its outer end for connecting the outletconduit to a suitable backing pump, such as a mechanical pump (not shown). A relatively small fine leak conduit 19 is attached to the outlet conduit just upstream from the outlet conduit flange and a valve 20 in the fine leak conduit serves to admit air into the pump as required.

The lower end of the pump casing is sealed by a bottom plate 21 hard-soldered to the pump casing. An upright, hollow vapor chimney indicated generally at 22 is disposed coaxially within the pump casing to extend from the bottom plate to a point just below the upper end of the pump casing. The lower end of the chimney comprises a cylindrical boiler wall 23 with an outside diameter only slightly less than the inside diameter of the pump casing. The lower end of the boiler wall is open and rests on the upper surface of the bottom plate. A plurality of notches 24 in the lower edge of the boiler wall provide communication between the annular space 25 formed between the boiler wall and the pump casing and the boiler interior. A pool of pump fluid 27, usually an organic liquid, is disposed in the lower end of the pump casing to a normal operating level 28. The boiler wall is centered with the casing by a plurality of screws 26 threaded into the boiler wall just below its upper edge so that the screw heads make point contact with the casing interior.

The upper end of the boiler wall terminates just above the lower edge of the pump casing outlet and is pro vided with a frusto-conical extension 29' hard-soldered at its lower end to the upper end of the boiler-wall and having a vertical extension 30 secured to an intermediate vertical, cylindrical conduit '31 by means of a circular clamp 32. A first ring 34 is hard-soldered t the upper end of the intermediate conduit 31 and its outer surface is beveled to match the innersurface of a hollow frusto-conical skirt 36 which is secured to the ring by means of machine screws 38 so that the lower edge of skirt 36 extends substantially below the upper end of conduit 31. A plurality of laterally extending slits 40 in the upper end of the intermediate conduit permit the escape of pump fluid vapor. A second ring 42 is press-fitted around the intermediate conduit just below the openings 40. An upper portion 44 of the second ring is beveled to extend parallel to the inner surface of the skirt 36 and provide a high pressure jet 46. A skirt 48 having a cylindrical vertical upper section 50 press-fitted into a recess 52 formed in the lower surface of the second ring 42 extends downwardly to a point near the lower end of the skirt 36 and then steps out to a second cylindrical vertical section 54 having an outside diameter slightly less than the inside diameter of the first upper skirt at its lower end to form a discharge opening 56. The lower portion of the first lower skirt is flared outwardly and terminates just above the pump casing outlet to provide a relatively narrow annular gap 58 be-' tween the lower edge of skirt 48 and the pump casing.

The upper end of skirt 36 is provided with a cylindrical vertical extension 60 which is attached by means of machine screws 62to the lower end of an upper cylindrical conduit 64 which terminates just below the upper end of the pump casing. A cap 66 is press fitted over the upper end of the upper conduit and effects a fluid type seal thereof. The cap extends downwardly a short distance and then steps out in diameter to a cylindrical vertical section 68 which is flared outwardly at its lower end to form a skirt 70'. A hollow inverted frusto-conical low pressure lower skirt 72 is provided with a cylindrical vertical section 74 at its lower end which is attached to the upper conduit adjacent the lower edge of skirt 70 by machine screws 76. A cylindrical vertical section 78 formed integrally at the upper end of the skirt 72 is spaced from the section 68 to form a low pressure jet 80. A plurality of openings 81 in the conduit 64 above the 'jet 80 permit vapor to flow from the conduit out the jet.

A hollow frusto-conical skirt 82 is provided with a cylindrical vertical section 84 at'its upper end which is secured to the upper conduit 64 below the skirt 70 by means of machine screws 86. A hollow inverted frustoconical skirt 88 is provided with a cylindrical vertical section 90 at its lower end which is attached to the upper conduit 64 just below the lower edge of skirt 82 by machine screws 92. An inwardly and upwardly extending section 94 is formed integrally with the upperend of skirt 88 to extend parallel with the inside surface of skirt 82 and provide an intermediate pressure jet 96. A plurality of openings 97 in the conduit 64 above the jet 96 permit vapor to flow from the conduit out the jet.

An external cooling coil 98 having an inlet 100 and outlet 102 is wound around and hard-soldered to the pump outlet conduit and the outside of the pump casing above the normal operating level of the pump fluid.

An internally threaded drain conduit 104 is provided in the lower portion of the outlet conduit and a plug 106 seals the lower end of the drain conduit. A baffle 108 extends across the lower portion of the outlet conduit just upstream from the drain conduit to prevent the return of any relatively volatile materials to the boiler.

An internally threaded locating nut 110 is hard-soldered to the upper surface and in the center of the bottom plate 21. A tie rod 112 externally threaded at its lower end is screwed into the locating nut and extends coaxially up the pump casing and chimney through the cap 66. The upper end of the tie rod is threaded externally to receive an acorn nut 114 which is hard-solderedto the upper surface of the cap 66.

Four cartridge type heaters 116 are sealed vertically and symmetrically through the bottom plate 21 so that their upper ends terminate just below the normal operating level of liquid within the boiler. Each heater is provided with power leads 118 for heating.

A conduit or internal quench coil 120 in the form of a flat spiral is disposed horizontally just above the upper ends of the heaters and just below the normal operating level of the liquid within the boiler. A quench coil outlet 122 and inlet 123 extend vertically through the bottom plate 21 and are sealed thereto by any suitable means such as soldering. The quench coil may be of any satisfactory material, for example, copper or aluminuin tubing.

The operation of the apparatus of Figs. 1 and 2 is as follows: a

The pump inlet is connected to a piece of work (not shown) and the pressure within the pump is reduced to its operating value, say about .5 millimeters of mercury, by means of a mechanical pumptnot shown).

earlier so that the liquid within the pump comes to its operating temperature shortly after a safe pressure is reachedswithin the pump. The pump fluid' in the boiler begins to boil and the vaporized liquid passes up the chimney and streams from each of the three jets, carrying gas from the Work down to the pump outlet where it is removed by the backing pump. Once the work is properly evacuated, it is sealed or tipped oif. The

heaters are then turned off and a cooling fluid, such as work is attached to the pump inlet and the pressure within the pump is again reduced by the backing pump to a safe value. The'heaters are then turned on and the cooling fluid is removed from the internal quench coil, for example by passing dry air therethrough. With the arrangement shown in Fig. 1 only the upper surface of' the pump liquid was cooled since this is the only part of the liquid exposed to atmospheric pressure andfthe re mainder'of' the pool is kept hot, Thus the pump is put back into action quickly since only a relatively small portion of the liquid need be re-heated. If desired, hot water or steam may be passed through the) quench coils to increase the heatingrate of thepump liquid. q

The advantages of this. invention can readily be app-re ciated from a specific example taken from actual operating conditions. In a pump of the type shown in Figs. 1 and 2 a pump liquid sold under the trade name of Oonvaclor 12 was used. Convaclor 12 is the trade name of Consolidated Vacuum Corporation for its pump fluid manufactured from chlorinated biphenyl and chlorinated polyphenyl compounds (sold under the trade name of Aroclor 1254) and having, a specific gravity (at 25 C.) of-1.5381.548, a boiling point at .5 mm.

Hg of 152 C., a molecular weight of 326, and-a re fractive index of 1639-1641. The normal operating ternperature of the Convaclor 12 pump fluid in the pump shown in Figs. 1 and 2 is 200 C. and by circulating .tap water through a quench coil of the typeillustrated in Figs. 1 and 2, the temperature of the pump fluidwas lowere'd from 200" C. to 180 C. in 20 seconds, the latter The heaters are turned on, or may have been turned on temperature being considered the maximum safe value for this type of oil. Thus atmospheric pressure may be admitted to the pump within about 20 seconds after cooling has started. However, in actual practice a safety factor is provided by passing cooling water through the quench coil for approximately 90 seconds to lower the pump fluid temperature to about 155 C.

Referring to Fig. 3, curve A illustrates how quickly the pump can be restored to operation after the pump fluid is cooled with the quench coil as described above. Starting with a pressure of approximately .5 mm. of Hg, the cooling water is blown out of the quench coil with air and the heating elements are turned on. Within 3% minutes the pump is operating and has reduced the pressure from .5 to millimeters of mercury. Curve B illustrates the length of time required by the same pump using identical pump fluid but cooled in the conventional manner, that is by simply turning off the heating elements and waiting for the pump fluid in the boiler to reach a safe temperature. Curve B demonstrates that a pump operated without the internal cooling coil requires approximately 9 minutes to achieve the same vacuum as is possible when the quench coil is used. This is not the entire story since cooling without the quench coil also takes approximately 9 minutes. The cycle time of a pump using the quench coil is approximately 5 minutes (1 /2 minutes for cooling plus3 /z minutes for re-heating and pumping down), while the cycle time of the same pump not using the quench coil is more than 18 minutes or more than three times as long. Thus the invention provides means for achieving a substantial reduction in the cycle time of a vapor-operated pump.

We have found that the position of the quench coil is not critical, and have obtained rapid quenching of the pump fluid at the surface of the pool with the quench coil located from about A1. of an inch above to about A of an inch below the normal operating level of the pump fluid. Even wider limits may be tolerated, of course, to the extreme of disposing the coils throughout the entire body of pump fluid, with the attendant increase in cycle time necessary to cool and reheat all of the pump fluid.

The use of a quench coil above the surface of the pool is illustrated in Fig. 4. In this embodiment the quench coil 120A is disposed just above the surface of the normal operating level 28 of the pump fluid 27. A quench coil outlet 122A and an inlet 123A extend vertically through the bottom plate 21 and are sealed thereto by suitable means.

We claim:

1. In a vapor-operated pump including a pot for containing a pool of liquid to be vaporized, a jet through which the resulting vapor is discharged, and means including a vapor chimney adjacent the pool for conducting the vapor from the pool to the jet, means for heating the liquid to an operating temperature, and a cooling conduit disposed within the pump near the pool surface for introducing fluid at a temperature below the operating temperature into the pump from the pump exterior and cool at least the surface of the liquid in the pool.

2. In a vapor-operated pump including a pot for containing a pool of liquid to be vaporized, a jet through which the resulting vapor is discharged, and means including a vapor chimney adjacent the pool for conducting the vapor from the pool to the jet, means for heating the liquid to an operating temperature, and a cooling conduit for circulating a fluid at a temperature below the operating temperature, the cooling conduit being disposed within the pot for cooling at least the surface of the liquid and having an inlet and outlet located outside the pump.

3. In a vapor-operated pump including a pot for containing a pool of liquid to be vaporized, a jet through which the resulting vapor is discharged, and means including a vapor chimney adjacent the pool for conducting the vapor from the pool to the jet, means for heating the liquid to an operating temperature, and a cooling conduit 6 for cireulatnig a fluid at a temperature below the operating temperature, the cooling conduit being disposed within the pool and having an inlet and outlet located outside the pump.

4. In a vapor-operated pump including a pot for containing a pool of liquid to be vaporized, a jet through which the resulting vapor is discharged, and means including a vapor chimney adjacent the pool for conducting the vapor from the pool to the jet, means for heating the liquid to an operating temperature, and a cooling conduit for circulating a fluid at a temperature below the operating temperature, the cooling conduit being disposed adjacent the pool surface for cooling at least the surface of the liquid and having an inlet and outlet located outside the pump.

5. Apparatus according to claim 4 in which the conduit is in the shape of a horizontal flat spiral.

6. In a vapor-operated pump including a pot for containing a pool of liquid to be vaporized, a jet through which the resulting vapor is discharged, and means including a vapor chimney adjacent the pool for conducting the vapor from the pool to the jet, means for heating the liquid to an operating temperature, and a cooling conduit for circulating a fluid at a temperature below the operating temperature, the cooling conduit being disposed within the pot just below the pool surface and having an inlet and outlet located outside the pump.

7. In a vapor-operated pump including a pot for containing a pool of liquid to be vaporized, a jet through which the resulting vapor is discharged, and means including a vapor chimney adjacent the pool for conducting the vapor from the pool to the. jet, means for heating the liquid to an operating temperature, and a cooling conduit for circulating a fluid at a temperature below the operating temperature, the cooling conduit being disposed within the pot just above the pool surface for cooling at least the upper portion of the liquid in the pool and having an inlet and outlet located outside the pump.

8. In a vapor-operated pump including a pot for containing a pool of liquid to be vaporized, a jet through which the resulting vapor is discharged, and means including a vapor chimney adjacent the pool for conducting the vapor from the pool to the jet, a heating element disposed in the pot below the surface of the liquid for heating the liquid :to an operating temperature, and a cooling conduit for circulating a fluid at a temperature below the operating temperature, the cooling conduit being disposed within the pot ,above the heating element and having an inlet and outlet located outside the pump.

9. In a high vacuum diffusion pump adapted for rapid transfer of heat to or from a pump fluid, a pump body, a vapor jet assembly positioned within said pump body, said jet assembly being smaller than said pump body and defining a pumping chamber with said pump body, at least one jet on said jet assembly being arranged to discharge a jet of difliusion pump fluid vapors downwardly into said pumping chamber, said jet assembly being open to vapors emanating from below, a boiler section at the bottom of said pump body capable of holding a pump fluid, a main heater means projecting into said boiler section, said main heater means being provided with a heat transfer passage capable of confining a heat transfer fluid, said heat transfer passage being in intimate heat transfer relationship with that surface of the main heater means which is in contact with the pump fluid.

References Cited in the file of this patent UNITED STATES PATENTS 2,150,685 Hickman Mar. 14, 1939 2,379,152 Hickman June 26, 1945 2,438,387 Colaiaco Mar. 23, 1948 2,572,449 Cortright Oct. 23, 1951 2,668,005 Wishart Feb. 2, 1954 2,703,673 Winkler Mar. 8, 1955