US3801225A

US3801225A - Vacuum pumps

Info

Publication number: US3801225A
Application number: US00252627A
Authority: US
Inventors: B Power
Original assignee: British Oxigen Ltd
Current assignee: BOC Group Ltd
Priority date: 1972-05-12
Filing date: 1972-05-12
Publication date: 1974-04-02
Anticipated expiration: 1991-04-02

Abstract

This invention provides an integral combination of a vapour vacuum pump, a baffle and an isolation valve as a single unit which offers substantial economies in construction and volume, compared with known pumps of the same performance, and which has only a single flange for attachment to the equipment to be evacuated.

Description

United States Patent Power 1' Apr. 2, 1974 1 VACUUM PUMPS 3,288,354 11/1966 Dennis 417 154 [75] Inventor: Basil Dixon Power, Sussex, England 3363830 1/1968 Landfomm 7/154 [73] Assignee: The British Oxygen Company FOREIGN PATENTS 0R APPLICATIONS Limited London England Canada [22] Filed: May 1972 Primary Examiner-Carlton R. Croyle [21] Appl. No.: 252,627 Assistant Examiner-Richard E. Gluck Related 0.5. pp ication Data j g 'g jgg FMPDBF'MM Dennison [63] Continuation-impart of Ser. No. 35,272, May 6,

1970, abandoned.

[57] ABSTRACT [52] US. Cl. 417/153, 417/154 This invention provides an integral combination of a [51] Int. Cl F041 9/06 6 m a ham nd an isolation valve 58 Field of Search 417/152, 153, 154 f as a smgle unlt wh1ch offers substantial economies 1n [56] References Cited construction and volume, compared with known 4 pumps of the same performance, and which has only 21 UNITED STATES PATENTS single flange for attachment to the equipment to be 2,806,644 9/1957 Warren 417/190 X evacuated, 2,935,243 5/1960 Sadler 417/153 X 3,165,255 1/1965 Landfors 417/153 8 Claims, 3 Drawing Figures PATENTEUAPR 21974 SHLEI 2 BF 3 ROUGHING VALVE BACKING VALVE AUXILIARY VACUUM PUMP VACUUM PUMPS BACKGROUND OF THE INVENTION This invention is a continuation-in-part of my U.S. patent application, Ser. No. 35272, filed May 6, 1970 and entitled Vacuum pumps, now abandoned.

In a vapour vacuum pump the gas to be pumped becomes entrained in a jet or jets of vapour of a heated condensible liquid. The entrained gas is transported by the vapour towards the pump outlet from which it is removed by a backing pump positioned downstream of the vapour pump.

The vapour carrying the entrained gas normally impinges on forced-cooled surfaces to encourage the vapour to condense and flow down to the boiler where it is again heated and recycled.

The volumetric speed of pumping of a vapour vacuum pump is a function of the annular area between the casing of the pump and the upper nozzle of the jet assembly. It is known to attempt to increase the volumetric speed of pumping by enlarging the casing in the region of the vapour nozzle. In some cases where this has been done, the enlarged casing section has been continued upwardly to the main inlet of the pump, without changing area. This has necessitated the isolation valve normally positioned upstream of the pump having a relatively-large internal diameter, which leads to an expensive construction. It has also been known to position a separate baffle or trap or both between the vapour pump and a separate isolation valve, but the resultant combination is expensive and cumbersome because of the multiplicity of large flanges and separate components.

In some cases where the casing has been locally enlarged (as for example, in the pump disclosed in U.S. Pat. No. 3,363,830 (Landfors)) the enlargement has been discontinued so that above the top of the jet assembly is provided an inlet port of diameter similar to that of the main part of the unenlarged casing of the vapour pump. When such ports had .baffles or. traps secured to them the small size of the port has dictated the use of baffles or traps having inlet ports of small area. This imposed undue restrictions on the gas flow, so that the advantage of the increased pumping speed due to local enlargement of the pump casing is largely lost. In addition, the multiplicity of flanged connections also led to a costly and cumbersome construction.

Accordingly the present invention aims at providing a composite pumping group with an integral baffle of low impedance to fluid flow and with a relatively small isolation valve so that, in combination with the belled housing of the vapour pump and baffle (r trap), a high volumetric pumping speed is achieved despite the pro vision of a relatively small, and therefore relatively cheap, isolation valve.

The present invention will now be described by way of example with reference to the accompanying drawlngs.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation, part in section, of a composite pumping group of the present invention;

FIG. 2 is a side elevation of the pump shown in FIG. 1, but taken from a direction perpendicular to that for FIG. 1, and showing the position of an integral backing- /roughing valve assembly when provided, and

2 FIG. 3 is a plan view of the' pump shown in FIGS. 1 and 2, withparts thereof being shown in section,

DESCRIPTION OF PREFERRED EMBODIMENT The composite pumping group of the present invention basically comprises a vapour vacuum pump and cold cap/

baffle assembly

46, 52, 54, having a housing 2 surrounding a jet assembly 4 and incorporating at its base a heater 6 for vaporising the oil from which the pumping vapour is produced. The housing is forcedcooled by passing a suitable coolant, such as water, through tubing 8 wrapped around the exterior surfaces of the housing 2 and in heat-transfer relationship therewith.

The other basic components of the pumping group of the present invention are a baffle or trap 10 positioned above the upper nozzle of the jet assembly, and an isolation valve 12 positioned above (i.e. upstream of) the baffle assembly 10, the valve 12 comprising an annular flange 14 with which a valve member 16 is intended to cooperate to form an isolation valve of the butterfly or quarter-swing type.

By the term baffle in this specification is meant an array of surfaces placed near the inlet of the vapour pump, i.e. above the top nozzle of the jet assembly, to impede the passage into the high vacuum part of the system of back-streaming and/or back-migrating vapour. The baffle surfaces are suitably cooled to encourage the condensation on them of incident vapour molecules, so that the vapour pressure within the evacuated system due to the vapour of a pumping liquid is never significantly greater than the equilibrium vapour pressure appropriate to the temperature of the cooled surfaces. When the baffle surfaces are cooled so deeply by a cryogenic liquid that the incident vapour molecules become'frozen to the surfaces then it is known to use the term trap for the baffle, although the basic mode of operation of the baffle is not changed.

As can be seen most clearly in FIG. 1, the housing 2 has an extension 18 leading to a supplementary condenser 20 having an outlet port 22 adapted, in use, to be connected through a suitable valve system 88 to the inlet of an auxiliary vacuum pump positioned downstream of the composite pumping group and used as both a roughing pump and a backing pump.

As can be seen from the drawing, the first part of extension 18 is frustoconical. Aligned with it is a tubular nozzle 19 projecting from the jet assembly. This provides a jet of vapour which cooperates with the extension to form a gas extraction nozzle operating on the venturi principle. It is mainly the vapour in this jetwhich is condensed in condenser 20. The tubing 24 of the auxiliary condenser 20 is usually connected in cascade with the tubing 8 cooling the main housing 2, although it is obviously within the purview of the present invention for condenser 20 to be supplied with a separate source of liquid coolant at a temperature different from that of the coolant circulating in tubing 8.

The housing 2 of the vapour pump has a cylindrical portion 26 encircling the lower portion 28 of the jet assembly. Contiguous with portion 26 of the housing is a belled-out portion 30 of housing surmounted by an inwardlytapering portion 32 terminating in a lip 34 of diameter equal to that of portion 26 of the housing. The flange 14 of the isolation valve is secured to lip 34 in a vacuum-tight manner, as by being welded. However, the valve plate 16 and the valve plate shaft 60 can be removed from flange 14 when necessary to furnish access tomembers positioned internally in housing 2.

The upper end of the lower part 28 of the vapour jet assembly is surmounted by a convergent-divergent member 36. At its lower end member 36 is spaced radially from the upper end of the lower portion 28 of the jet assembly 28 to define with it an annular opening 38 which acts as the lower vapour nozzle.

Supported onthe top end of member 36 is a member 40 similarly defining with member 38 an annular gap 42 functioning as the upper vapour nozzle.

Extending inwardly from the housing 2 are supports 44 for a ring member 46 acting as an integral part of the baffle 10. The ring 46 has a single turn of piping 48 wrapped around it and in communication, by means of. portion 50, with the piping 8, so that ring member 46 is at the temperature of the housing 2. Ring member 46 supports a domed cold cap 52 from which depends a cylindrical skirt 54. Because the skirt 54 is substantially at the same temperature as the external housing 2, it acts as a cold cap circumscribing the nozzle to control or inhibit the'back-streaming or back-migration of the vapour towards the. isolation valve 12 from the nozzle lip region.

It will thus be seen that the cold cap 52, ring 46, and the circumscribing andtapering surfaces 32 of housing 2 cooperate to form a baffle of the chevron-and-plate type. At the low pressures attained in the interior of the housing 2 when the pump is in use, the vapour molecules tend totr'avel in straight lines over long distances, as they rarely collidewith other molecules. For efficient capture of the molecules the baffle has to be'designed so that there is no line-of-sight through it. This ensures that any back-streaming or back-migrating vapour has to impinge on at least one surface of the trap before it can .pass out through the isolation valve. By coolingthis surface sufficiently the molecules tend to be captured by the baffle when they impinge on it, and therefore do not rebound. It will be seen. from the drawing that a grazing tangent to both lip 34 and ring 46 will meet portion 30 of the housing at a point positioned above the level of the upper nozzle 42 of the jet assembly. The efficiency of, the baffle is even further increased by the provision of skirt 54 of the cold cap which screens adjacent parts of the housing from the view of nozzle 42. This ensures that any vapour tending to be emitted laterally from the nozzle, or with a velocity components upwards as viewed, falls on skirt S4 and is there condensed into oil droplets which fall back into the boiler.

It is not essential that the cold cap assembly be cooled artificially as any vapour molecules hitting the underside of the assembly would tend to rebound on to the cooled housing 2 where they would be captured before reaching the isolation valve 12. However, it preferably is cooled in order to increase its efficiency.

Positioned internally in the cap 52 is a frustoconical member 56 adapted to engage an extension 58 from member 40 to act as a stabiliser for the upper end of the jet assembly 4. A compression spring 41 extends between the cap 52 and the jet assembly to provide a resilient bias holding the jet assembly together during transit of the vacuum pump.

The supports 44 are arranged so that they present as low an impedance as possible to the flow of gas from the isolation valve 12 through into the interior of housing 2.

The effective speed of a vapour pump is a function, amongst other things, of the size of the annular area between the upper nozzle 42 of the pump and the adjacent portion of housing 2. It will be seen that, because of the belied-out portion 30 of the housing, this area is relatively large, leading to a pump of higher volumetric pumping speed than is usually associated with an isolation valve 12 of the relative size shown. This is a considerable advantage because a significant component of the cost of a vapour vacuum pump installation is that of the separate baffle and isolation valve hitherto required. The pump housing, the baffle and the valve require machined flanges to ensure vacuum-tightness, and these flanges are expensive. Thus considerable economies are achieved by combining the separate integers into an integral unit having only one mounting flange,- and having a significantly-reduced height compared with known pumping installations of the same performance.

It will thus be seen that the belled-out portion of the housing carries out the dual functions of increasing the speed of the vapour pump and acting as a cooled baffle.

Diagrammatically indicated in FIG. I is a shaft 60 which is connected internally of flange 14 to the valve plate 16. The'precise manner in which the shaft 60 is connected to valve plate 16 is conventional and does not form part of the subject-matter of the present application and so will not be described herein in greater detail. In one embodiment the interconnection is such that the shaft 60 requires to be turned through I to move the valve plate 16 between its open and sealing positions, which are angularly spaced apart by This indirect connection of the shaft 60 to valve plate 16 enables the valve plate to be translated between a closed position (in which'it is oriented as illustrated in FIG. 1) and a sealing position in which it is urged so firmly towards the frusto-conical seating surface 62 of flange 14 that an 0-ring seal 64 on valve plate 16 is deformed into vacuum-tight contact with the seating surface 62. Matters are arranged so that reverse rotation of shaft 60 first effects translation of plate 16 from its sealing to its closed position before the valve plate is moved through 90 to its fully-open position in which it pres ents minimum impedance .to the flow of gas through the isolation valve.

The heater 6 is connected to a terminal box 66. As the manner by which the heating current is supplied to the heater, and is controlled, does not form part of the subject-matter of the present invention it will not be described herein in further detail. The level of the vaporising oil used in the vapour pump can be measured by means of a dip stick assembly 68 shown in FIG. 2, al though of course other methods of measuring or indicating the amount of oilcan be used. When the supply of oil runs low then additional oil can be supplied through conduit 70.

Although a large proportion of the vapour issuing from the nozzle 38 and 42 is condensed while still inside housing 2, a proportion of the vapour is entrained with the gas drawn into the jet of vapour issuing from nozzle'19, and so passes through extension 18 into the auxiliary condenser 20. The condensation of most, if not all, of this vapour is achieved by the cooling coil 24. The resulting condensate is able to flow back into the interior of housing 2, and from there to the heater 6, after first flowing through one or more orifices '72 in the wall of the inner member 74 of the condenser 20. This means that substantially only the gas being pumped issues through port 22 to the valve assembly 88 positioned upstream of the auxiliary roughing/backing vacuum pump.

In the remaining figures of the drawings, those parts already shown in FIG. 1 are given the same references.

In FIG. 2, the main additional item illustrated is a conduit 76 extending from flange 14. At its upper end as viewed conduit 76 is in communication with the upstream face of the valve plate 16 at all positions thereof. This means that conduit 76, which will be referred to as the bypass conduit for reasons given below, is at all times in communication with the interior of equipment coupled to flange 14. At its other end bypass conduit 76 terminates in a union 78 coupled permanently or temporarily to the abovementioned valve assembly 88 of which an outlet 90 is intended to be connected to the inlet of the said auxiliary pump. The outher inlet 89 of assembly 88 is coupled to the outlet 22 of the vapour pump.

This arrangement enables the coupled equipment to be pre-evacuated (or pumped down) by the auxiliary pump while the isolation valve remains sealed but with the vapour pump working. This is done through a roughing valve (forming part of assembly 88) in series with conduit 76 and the auxiliary pump. When a suitable pressure has been reached the roughing valve is closed and a backing valve (in series with outlet 22 and the auxiliary pump and also in assembly'88) is opened. Thereafter the isolation valve 12 is opened to connect the interior of the equipment with the vapour pump.

When access is required to the interior of the equipment being evacuated the isolation valve 12 is closed but the auxiliary pump continues to supply backing pressure to the vapour pump. Air isthen admitted to the equipment through a separate admittance valve. When the equipment next requires to be evacuated the backing valve is closed and the roughing valve opened. When the equipment has been pre-evacuated the abovementioned sequence is restarted.

It is within the purview of the present invention for the backing/roughing valve assembly 88 to be an integral part of the pumping group, in which case there is provided a unit having the appearance shown in FIG. 2.

In FIG. 3 are shown further details of the construction of the isolation valve 12. The shaft 60 is provided with holes through which pass screws 80 securing the valve plate 16 to shaft 60. Externally of flange 14 of the shaft 60 is provided with a slot 82 by means of which an operating lever can be keyed to the shaft to rotate it in order to operate the valve. The lever may be actuated manually, electrically, pneumatically or otherwise.

Positioned beneath the valve plate and extending diametrically across the interior of the housing is a strap 84 which is suitably secured at its ends to the housing 2, either directly or indirectly. The center of the strap 84 is adapted to bear down on the domed cap 52 to bias it resiliently into firm engagement with ring member 46. This is in order to keep the cap in its operating position during operation and transport of the composite pumping group so that the upper end of the vapour jet assembly is always supportedlaterally. The strap 84 is so secured to the housing that it can be dislodged from its support and removed through the opening defined by lip 34 when it is desired to obtain access to, or remove the jet assembly from, the'interior of housing 2.

To permit this removal the upper surface of the domed cap 52 has projecting from it a pair of lugs 86, and the extension 58 from the jet assembly has its surface knurled. The arrangement is such that when the jet assembly has to be removed for servicing or replacement, the isolationvalve plate 16 is detached from its shaft 60. The'plate 16 is then removed, and the shaft 60 withdrawn axially, to provide unobstructed access to the interior of housing 2. The strap 84 is then removed, thus permitting removal of the cover 52 and skirt 54. When this has happened the vapour jet assembly can be withdrawn through the opening defined by lip 34. The reverse procedure takes place when a jet assembly is to be positioned in the interior of housing 2.

It will thus be seen that the present invention provides a composite pumping group of high volumetric speed in relation to the size of the isolation valve; which has an integral baffle of high efficiency; which is able to be dismantled easily to permit servicing or replacement of the vapour jet assembly, without disturbing the pump as a whole; which is of reduced overall height, and which has only a single mounting flange.

I claim:

1. A vapour vacuum pump including a vertically arranged-housing having an inletat its upper end and seating an internal vapour jet assembly at its lower end, means defining upper and lower vapour nozzles within said hoousing; a flanged isolation valve secured to the inlet in a vacuum-tight manner, means for cooling the housing by heat transfer to a fluid coolant, said housing flaring outwardly and downwardly from below the inlet defining a region of maximum internal diameter from which it tapers inwardly and downwardly to a cylindrical portion circumscribing the lower part of said vapour jet assembly, saidportion of maximum internal diameter positioned adjacent and extending above the level of said upper vapour nozzle, a plate assembly defining with said housing an annular gap for the flow of gas from the inlet to the interior of the housing, said plate assembly including'a ring fixed to said housing and having a cap detachably mounted thereon to cover the opening in said ring, the internal diameter of said ring being greater than the external diameter of said vapor jet assembly, said cap including a depending skirt dimensioned to circumscribe and extend below said upper nozzle, said maximum diameter and flared portions of the housing defining with said plate assembly a baffle inhibiting the back-streaming of vapour molecules to the inlet, and said internal diameter of the cylindrical portion of said housing being approximately equal to the internal diameter of the inlet.

2. A vapour vacuum pump as claimed in claim 1, in which the plate assembly includes cooling means.

3. A vapour vacuum pump as claimed in claim 2, in which the coolant for the plate assembly is the same as that which is used to cool the housing.

4. A vapour vacuum pump as defined by claim I in which said cap includes a depending member in contact with a projection on the top of said vapour jet assembly to preclude lateral movement thereof.

5. A vapour vacuum pump as defined by claim 1 in which a resilient strap is secured to said ring and extends diametrically across the top of said cap to bias said cap into engagement with said ring.

6. A vapour vacuum pump including a vertically arranged housing having an inlet at its upper end, an isolation valve secured to said inlet, said valve including an annular flange attached to said housing encircling said inlet, a rotary shaft extending through at least a portion of said flange and across said inlet, a valve plate detachably mounted on said shaft and seated within said flange, said shaft dimensioned for axial withdrawal from said flange to provide unobstructed access to the interior of said housing through said inlet, a vapour jet assembly including upper and lower vapour nozzles positioned within said housing and seated at the lower end of said housing, means for cooling said housing by heat transfer to a fluid coolant, said housing including portions flared outwardly and downwardly from the inlet to a region of maximum internal diameter, said housing further configured to taper inwardly and downwardly connecting with a cylindrical housing portion circumscribing the lower portion of said jet assembly disposed therewithin, said portion of maximum internal diameter being disposed at least partially at the level of and encircling the uppermost vapour nozzle, a plate assembly which together with said housing defines an annular gap for the flow of gas from the inlet to the interior of said housing, said portion of said housing of maximum internal diameter and said flared portions of said housing together with the plate assembly defining a baffle inhibiting the backstreaming of vapour molecules from the interior of said housing to the inlet when said pump is in operation, the diameter of the opening in said flange of said isolation valve being approximately equal to the internal diameter of the cylindrical portion of the housing and of greater diameter than the maximum external diameter of said vapour jet assembly.

7. A vapour vacuum pump as claimed in claim 6 in which said flange includes conduit means selectively connectable to the interior of said pump and in communication with the space above the valve plate when the latter is in its closed position.

8. A vapour vacuum pump as defined by claim 7 in which an auxiliary vacuum pump assembly is selectively connectable with the said conduit.

Claims

1. A vapour vacuum pump including a vertically arranged housing having an inlet at its upper end and seating an internal vapour jet assembly at its lower end, means defining upper and lower vapour nozzles within said hoousing; a flanged isolation valve secured to the inlet in a vacuum-tight manner, means for cooling the housing by heat transfer to a fluid coolant, said housing flaring outwardly and downwardly from below the inlet defining a region of maximum internal diameter from which it tapers inwardly and downwardly to a cylindrical portion circumscribing the lower part of said vapour jet assembly, said portion of maximum internal diameter positioned adjacent and extending above the level of said upper vapour nozzle, a plate assembly defining with said housing an annular gap for the flow of gas from the inlet to the interior of the housing, said plate assembly including a ring fixed to said housing and having a cap detachably mounted thereon to cover the opening in said ring, the internal diameter of said ring being greater than the external diameter of said vapor jet assembly, said cap including a depending skirt dimensioned to circumscribe and extend below said upper nozzle, said maximum diameter and flared portions of the housing defining with said plate assembly a baffle inhibiting the back-streaming of vapour molecules to the inlet, and said internal diameter of the cylindrical portion of said housing being approximately equal to the internal diameter of the inlet.

4. A vapour vacuum pump as defined by claim 1 in which said cap includes a depending member in contact with a projection on the top of said vapour jet assembly to preclude lateral movement thereof.