US3433297A - Selectively cooled motive fluid trap for a vacuum steam pump - Google Patents

Description

March 18, 1969 3,433,297

M. KOHLER SELECTIVELY COOLED MOTIVE FL TRAP FOR A VACUUM S M PUM Filed Aug. 1967 Jnvenfor:

5 A77'0ENEVS United States Patent C 3,433,297 SELECTIVELY COOLED MOTIVE FLUID TRAP FOR A VACUUM STEAM PUMP Marcel Kohler, Balzers, Liechtenstein, assignor to Balzers Patentnnd Lizenz-Anstalt, Balzers, Liechtenstein Filed Aug. 21, 1967, Ser. No. 661,903 Claims priority, application Switzerland, Aug. 23, 1966,

12,25 1/ 66 US. Cl. 165-40 6 Claims Int. Cl. F28b 9/10; F28d 1/06 ABSTRACT OF THE DISCLOSURE A motive fluid trap for a vacuum steam pump formed by a trap housing mounted on the steam pump. Means are disposed within the trap housing for condensing the motive or fluid vapor including a support block secured to the trap housing. A nozzle cap for a nozzle, located in the upper part of the pump, is positioned just below the support block. A shield for the nozzle cap is dependently secured to a thermally responsive support element mounted on the block whereby the shield is movably positionable with respect to the nozzle cap in relation to the temperature to which the thermally responsive support element is exposed within the trap housing.

The prior art The present invention is directed to a motive fluid trap for vacuum steam pumps and, more particularly, to a motive fluid trap which employs different coolants adapted to operate at different temperatures.

The ability to cool a motive fluid trap in a vacuum steam pump to different temperatures would be particularly useful in adapting the pump to various operating conditions. In selectively cooling the motive fluid trap it is useful if different coolants capable of operating at different temperatures are employed. When a stronger motive fluid return flow is permissible, or if the pump is separated from its receiver during operation, as by a plate valve, then using water as the coolant is appropriate. However, if the motive fluid vapor pressure in the receiver is to be kept as low as possible to obtain an optimum high vacuum then cooling with liquid nitrogen is preferable. If a coolant is employed which would tend to solidify or freeze the motive fluid within the trap, it is important to limit the amount of freezing as much as possible, because the operation of the pump would be disturbed by any considerable loss of motive fluid due to freezing.

It has been known in the past to use a steam jet diffusion pump employing a condenser disposed between the pump and the space to be evacuated, see German Pat. No. 1,000,965. In this arrangement the condenser is maintained at a temperature of 40 or less, however, it utilizes a condenser plate located in the path of the gas particles and the temperature of the plate is maintained high enough that the motive fluid from the pump in the vicinity of the plate condenses thereon only in liquid form.

For another trap employed to cool steam to a low temperature by condensing vapors in a vacuum system, see German provisional Pat. No. 1,071,890. In this arrangement the vapor discharged into the coolant vessel or trap evaporates toward the exterior or surface of the trap and in so doing, it cools the separating surfaces within the connecting line between the vacuum receiver and the motive fluid pump. Accordingly, the separation surfaces are at a temperature whereby the condensable vapors are separated out in the liquid state, and a passage of the condensed fluid is provided from the coolant vessel whereby the condensed fluid serves to cool other separation surfaces whose temperature is above that of the coolant fluid.

3,433,297 Patented Mar. 18, 1969 These known arrangements were not intended for selective operation with coolants of different temperatures, and as a result no problem arose due to the effect of different temperatures operating on the structure of the coolant trap and its associated pump.

Summary of the invention It has been found that a considerable portion of the motive fluid return flow in a vacuum steam pump originates in the zone of the motive steam jet from the uppermost nozzle, and this return flow can be greatly reduced by providing the zone with an annular or hood-shaped shield for the cap on the nozzle. Further, the shield can also serve to protect other parts of the steam coolant trap against excessive heating by the radiation from the hot nozzle. Where a shield is employed over the nozzle cap, and different fluids are used to selectively cool the trap, such as water and liquid nitrogen, due to the different temperatures of the fluids employed, a problem results in that if good heat transmission exists between the trap and the shield when the lower temperature coolant is employed, there is a tendency for the steam to freeze on the surface of the trap and thereby disturb the operation of the pump. Conversely, if a heat resistance is placed between the shield and the coolant trap, which prevents proper condensation of the motive fluid, then where water is used an ineffec tive cooling effect is obtained on the shield and the advantages sought to be obtained by the use of this structure are largely offset. It would be possible to provide a separate cooling arrangement for the shield using a special coolant to attain the proper operating temperature for the shield, however, such an arrangement would be costly and complicated to operate.

The present invention is directed to a motive fluid trap for a vacuum steam pump wherein the steam is condensed by selectively cooling it with coolants of different operating temperatures. In accomplishing this result, a shield is provided over the nozzle of the pump, and the shield is arranged so that it can be movably positioned in relationship to the nozzle cap for assuring the proper operating conditions for the vacuum steam pump.

Accordingly, it is a primary object of the present invention to utilize a thermally responsive support member in a motive fluid trap for a vacuum steam pump which will respond to the temperature within the trap to properly position and support a shield member in relationship to a nozzle cap in the vacuum steam pump itself.

Another object of the invention is to utilize a bimetallic element as the thermally responsive support element for the shield in a motive fluid trap selectively cooled by coolants of different temperatures.

Yet another object of the present invention is to provide a combined motive fluid trap and vacuum steam pump which permits selective cooling of the motive fluid within the trap while maintaining the optimum efficiency of the pump regardless of the coolant temperature employed.

Therefore, the present invention is directed to a motive fluid trap wherein different coolants operating at different temperatures can be circulated to condense the vaporized motive fluid employed in a vacuum steam pump. The trap is positioned above the uppermost nozzle of the vacuum steam pump and a cap separates the nozzle and the trap. The trap is comprised of a support assembly which includes a thermally responsive support element and a shield dependably supported from the support element and movably positionable in relationship to the nozzle cap. In response to the temperature within the trap the support element either expands or contracts and accordingly positions the shield which is secured to it.

The support assembly for the shield, and more specifically its thermally responsive support element, must be adapt ed to the different coolants which are used in the trap whereby the shield supported from the element will assume a position relative to the trap such that the temperature of the shield is within permissible limits for reliable operation of the pump. In other words, if a coolant such as water at 15 C. is employed, the heat transmission from the trap to the shield, which is determined by the amount of radiation and heat conduction from the nozzle, must be better than exists where a lower temperature coolant, such as liquid nitrogen, is utilized. One successful embodiment of the invention consists in a construction wherein a thermally responsive support element arranged within the trap permits the shield to touch the nozzle cap when a higher temperature coolant is employed but which causes the shield to be spaced from the nozzle cap when the arrangement is being cooled by a lower temperature coolant, such as a liquid gas.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawing and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.

Description of the drawing The drawing discloses a vertical sectional view of a coolant trap and a portion of a vacuum steam pump embodying the present invention.

Detailed description of the invention In the drawing the upper portion of a vacuum steam pump is shown formed by a housing 1 with a flange 2 disposed at its upper end. Secured to the flange 2 is another flange 3 forming part of a motive fluid trap 4 which extends vertically upward above the housing 1 of the vacuum steam pump. Within the space 12 in the housing 4 a plurality of right angle collection plates are disposed in vertically spaced arrangement supported by a number of struts from a support block 11 which is supported on the housing 4. The collection plates 59 are cooled by circulating a coolant through tubes 13 secured to the plates. In this arrangement the coolant flowing through the tubes 13 cools the collection plates, which, in turn, condense the steam vapor as it passes over them but permits the gas mixed with the vapor to escape from the space 12.

On the upper surface of the block 11, uprights 14 and 15 support a horizontally arranged thermally responsive bimetallic element 16. The block also contains a centrally arranged bore or opening 17 through which extends a support rod 18 attached at its lower end to a shield and at its upper end to the bimetallic element 16. The shield 20 is positioned above the nozzle cap 19:: located on the nozzle 19 of the vacuum steam pump. The position of the shield relative to the nozzle cap is determined by the position assumed by the thermally responsive sup- 'port element 16 within the motive fluid trap.

It can be readily appreciated that, with decreasing temperatures, the thermally responsive support element 16 will contract and will assume a flat or horizontal position, and as the temperature within the trap increases, the support element 16 will tend to expand and with the uprights 14 and 15 set relatively stationary, the support element 16 will tend to curve downwardly with its center, to which the rod 18 is secured, assuming the lowermost position. Since the shield is secured to the rod 18, the position of the shield will depend on the position assumed by the support element. When the higher temperature coolant is used, the shield will be in its lower position supported directly on the nozzle cap 19a and as the temperature of the coolant decreases, the shield Will lift off the cap to a position spaced some distance from it depending upon the operating conditions desired for the pump.

While one specific embodiment of a thermally responsive support element has been shown in the drawing, based on the principle described herein, it will be appreciated that a number of different support elements may be employed which are sensitive to temperature variations within the trap and which will provide the proper orientation of the shield relative to the nozzle cap of the pump, based on the temperature within the trap. The arrangement employed will depend on the operating conditions of the pump and must be capable of providing reliable and efficient operation.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. A motive fluid trap for a vacuum steam pump, whereing different coolants operating at different temperatures can be circulated to condense the vaporized motive fluid, comprising a vacuum steam pump nozzle, a cap positioned on said nozzle, a trap member dis-posed above said nozzle comprising a support assembly including a thermally responsive support element, a shield located below said support assembly and disposed above and movably positionable in relationship to said nozzle cap, said shield dependently secured to said thermally responsive support element whereby as the support element expands and contracts in response to the temperature Within said trap member the shield supported from the thermally responsive support element will move toward and away from the nozzle cap respectively.

2. A motive fluid trap as set forth in claim 1 wherein said shield is movably positionable between a lower position in contact with said nozzle cap and an upper position spaced from said nozzle cap.

3. A motive fluid trap as set forth in claim 2 wherein said trap member comprises a housing, said support assembly located within said housing and comprising a block member secured to said housing and having an opening arranged therethrough, said thermally responsive support element mounted on said block member, a vertically oriented support rod extending through the opening in said block member and secured at its upper end to said support element and at its lower end to said shield.

4. A motive fluid trap as set forth in claim 3 wherein a pair of support columns extend upwardly from said block member, said thermally responsive support element is horizontally oriented and is attached to and extends between said columns.

5. A motive fluid trap as set forth in claim 4 wherein said thermally responsive support element comprises a bimetallic element.

6. A motive fluid trap as set forth in claim 3 wherein a plurality of annular collection plates are positioned in said trap member and are supported theerin by said block member, and conduit means located within said trap member for circulating coolant fluid therethrough for cooling the surfaces of said collection plates.

References Cited UNITED STATES PATENTS 1,323,813 12/1919 Baruch 73 1,461,726 7/1923 Crafts 165-73 3,175,373 3/1965 Holkeboer et al 165111 LLOYD L. KING, Primary Examiner.

C. SUKALO, Assistant Examiner.

US. Cl. X.R.

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