US2535796A - Vacuum pump - Google Patents

Description

Dec. 26, 1950 K. c. D. HICKMAN VACUUM PUMP 2 Sheets-Sheet 1 Filed Jan. 16, 1946 FIG.1.

KENNETH C'.D. HICKMQN INVENTOR ATTORNEY Dec. 26, 1950 K. c. D. HICKMAN VACUUM PUMP 2 Sheets-Sheet 2 Filed Jan. 16, 1946 KENNETH D. HJCKPfllN INVENTOR ATTORNEY Patented Dec. 26, 1950 VACUUM PUMP Kenneth C. D. Hickman, Rochester, N. Y'., as-

signor, by mesne assignments, to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application January 16, 1946, Serial No. 641,478-

3 Claims. (Cl. 230-10,1)

This invention relates to an improved highvacuum pump of the ejector type designed to operate on phlegmatic liquids, the entire operating assembly being held within a casing of the kind, usually employed for condensation pumps.

Condensation pumps have previously been constructed with a number of jets positioned in series on a pipe with the smallest jet near the intake. This construction is sat'sfactory and relatively eflicient in smal sizes but it becomes less and less efficient as the diameter increases. In partiular, the fore. pressure against which the entire assembly. will pump, diminishes rapidly with increase. in diameter. The reason for the failure to operate against high fore pressure is associatedwith the narrow clearances and large frictional surfaces to which the vapors are exposed. It has been known to replace the lower, large annular jet with smaller pairs of ejector and diffuser nozzles, the latter being embedded in a mass of heat-conducting metal cooled. by the walls of the pump. Such a construction has been costly and difficult to assemble. Also, the weight of metal in a large pump, such as twelve inch diameter or more, may reach hundreds or even thousands of pounds, requiring heavy-walled casing-s and staunch supporting platforms.

The present invention has for its object to provide. an improved ejector-type diffusion pump. Another object is to provide a vacuum pump which can operate against unusually high fore pressures. Another object is to provide a combination of annular jets and eiector-difiuser jets inwhich the weight of constructing metal is drastically reduced. Other objects will appear hereinafter.

These and other objects are accomplished by my inyentionwhic-h includes an ejector-type diirusion pump having one or more sets of ejector-type nozzles and. difiusers constructed of thin-walled metal and maintained within the housing of a (infusion. pump. According to this invention, directcooling of the. diffusers is obviated by providing large separate condensing surfaces to absorb the. actuating vapor, and, in some cases, by providing a cooled stream of condensate to flow over the top of the diffusers, thereby cooling them for emcient operation.

In the following description I have set forth certain preferred embodiments of my invention butit is to be understood that these are given by way of illustration and not in limitation thereof;

In the accompanying drawing wherein like numbers refer to like parts: 7

Fig. 1 is a vertical section of a two-stage pump embodying the features of my invention and;

Fig. 2 is a fragmentary perspective view, partly in section, of a modification of the pump illustrated in Fig. 1 said view covering the portion. of the pump. adjacent to the low pressure jet of the pump. of Fig. 1,.

Referring to Fig. 1, numeral 2 designates a cylindr cal pump casing provided with an integral. gas-tight base 4, to which is attached a heater 6. Numeral 8 designates a. flange: at. the top of the. casing which is adapted. to be attached toithe systern to be evacuated. Numeral to. designates: a conduit; adapted to be connected tov a. vacuum. pump (not shown).

Numeral, l2. designates a cylindrical vapor chimney positioned concentric with casing 2, which is expanded outwardly at l4. so that the lower portion thereof approaches the wall of casing 2. Numeral l6 designates an annu ar collar integral with chimney t2, the top plate of which. supports a second cylindrical chimney 18. which serves todeliver vapors to jet 2!). formed by umbrella cap 22 and truncated. cone 24-.

Collar It, supports six elbow shaped conduits. 28. which, turn downwardly and support jet nozzles 28. Numeral designates a diffuser tube element which is constructed of thin walled metal and which is formed so that it crosses, the space between chimney IA and the, inside wall of. casng; 2. This diffuser eement carries six diffuser tubes" 32 which cooperate with jet nozzles 28 to formv six ejector pumps operating in parallel. Numeral 34 designates a supply of low vapor pressure organic liquid used as an actuating fluidand nu meral 35 designates an insulatim cylindrical. casing for chimney l2 and. acts. to prevent great loss of heat from thevapors passing. therethrourrh.

In operating the apparatus shown in l, flange 8, is connected to the system in which. a high, vacuum is to be produced and conduit tilis. connected. to the backing pump. (not shown) which is put into operation. Heater 5 is, then actuated and. vapors from pump. fluid 34. in the boiler pass upwardly through conduits l2: and I8.-

Vapors passing. through 18 are reversed. in their direction andissue as. a high velocitystream from; nozzle 20.. Gases difiusing from. the. system to be. euacuat'ed are entrained in. these vapors and: are; forced. downwardly into. the, space between.

nozzles. 28. and diffuser tube; 32, These, gases are:

then entrained; in the high velocity stream of vapors. which. passes through, elbows 215 into nozzles wand. are. forced into thence. into... conduit diffuser tubes 3L and. to. from. which. they; are;

removed by the backing pump. Condensed working fluid collects on the walls of casing 2 and diffuser tubes 32 and flows by gravity back into the body of the pump fluid 34 by way of the space between H and the inside wall of easing 2. The pump fluid is again evaporated and the pumping action described is continuous.

The following table illustrates the improved results obtained by the construction shown in Fig. 1 (column A) as compared with a similar pump of the same size operating under the same conditions but having a single umbrella jet instead of the six ejector type nozzles 28, shown in the drawing (column B).

Maximum speed (l/sec.) 370 250 Forepressure breakdown at 2 kw. heater input:

Speed at high vacuum of 50 microns (l/3) It will be noted that the pump described herein gives markedly better results. Thus, the maximum speed is 370, as compared with 250. The forepressure at which the pump efiiciency breaks down (forepressure breakdown) is also markedly improved.

Referring to Fig. 2 numeral til designates a circular disc having an outer edge 52 which is turned inwardly and provided at the center with a collar 44 which fits over the outside of chimney l2 and which is welded thereto. Numeral designates a similar element having an outwardly turned edge .8 and provided with a collar 59 at the center thereof which is welded to and supports chimney l8. Numerals 52 and 54 designate a plurality of openings in plates ii and it respectively in which are placed short cylinder elements 56 which are welded to the edges of openings 52 and 54 and serve to support chimney it and disc 45 in the manner illustrated. Numeral 66 designates an annular collar, the upper edge of which is in contact with and welded to the inside wall of easing 2. Numeral 62 designates an annular collar, the upper edge of which is welded to the outside wall of chimney l2 as indicated. Collars 50 and 62 cooperate to form an annular diffusing space 54 and i2 and it cooperate to form an ejector nozzle having an annular throat and mouth and which is adapted to deliver an annular stream of pumping vapors over the entire cross sectional area of the pump casing at the point in the casing where they are located.

During operation of the jet illustrated in Fig. 2 vapors pass upwardly through chimney l2 and extension chimney It. Part of the vapors pass into the space between plates 49 and i and issue downwardly as a stream through the annular nozzle 58 formed between walls 52 and 48. This annular stream of vapors passes into the cooperating annular difiuser tube 5 and forces gases therethrough and into the base of the pump as described in connection with Fig. 1. The condensed vapors flow into the boiler as previously described. Openings 5 3 permit gases flowing from the low pressure end of the pump to pass therethrough and into the vapors issuing from jet nozzle 58. These gases also pass between edge 48 of the nozzle 58 and casing 2 so that the aperture for flow of gases is thus materially increased.

The thin walled construction is simple and cheap to construct and can be assembled without difiiculty. Also, it adequately conducts heat away from the working vapors. This cooling effect is increased by the condensed fluid from upper jet or jets as it flows over the surface of the thin walled diffusers. It is, therefore, unnecessary to have positive cooling of the thin walled diffuser tubes, although cooling can be applied without departing from the spirit or scope of my invention. Also, if further cooling is desired it can be obtained by increasing the condensing area of the condenser walls or applying cooling fiuid thereto, thus further lowering the temperature of the thin walls of the diffusers by conduction and by the lower temperature of the condensate flowing thereover. While I have illustrated my invention in connection with a pump having ejector nozzles and cooperating thin walled diffusers at one stage several stages may be provided with the same construction. Thicknesses of about /64 inch to inch for the walls of the diffuser tube are generally satisfactory. The thicker walls would be used for larger pumps. The main requirement is that the walls should have sufiicient thickness to maintain their shape during shipment or use. It is, therefore, apparent that thicker or lighter walls than mentioned may be used.

What I claim is:

1. A high vacuum diffusion pump comprising, in combination, wall means forming a pump chamber having an inlet and outlet substantially spaced from said inlet along said chamber, chimney means within said chamber and generally coaxial with said chamber, said chimney means extending from the region of said outlet to the region of said inlet, means for supplying pumping vapors to said chimney means, an umbrella jet disposed in the region of said inlet and arranged to receive pumping vapors from said chimney means and discharge said vapors in an annular stream in said chamber in a direction away from said inlet, ejector nozzle means disposed about said chimney means on the outlet side of said umbrella jet and comprising a plurality of annularly arranged ejector nozzles arranged to receive pumping vapors from said chimney means and to discharge said vapors away from said inlet, and diffuser tube means annularly arranged about said chimney means, said difiuser tube means comprising a plate-like upper member bridging the space between said wall means and said chimney means around the circumferential extent of said chimney means, said upper member being marginally secured to said wall means and to said chimney means, said upper member having a plurality of openings therethrough in substantial alignment with said ejector nozzles, and a plurality of thin-walled metal diifuser tubes secured to said upper member and dependent therefrom, each said diffuser tube communicating with one said opening in said upper member, said difiuser tubes throughout their downward extent being spaced from said wall means and from said chimney means, the walls of each said diffuser tube being of substantially uniform thickness throughout the extent of said diffuser tube, said walls being convergent downwardly for a substantial distance from said upper member and thence divergent to the lower end of each said diffuser tube.

2. A high vacuum diffusion pump comprising a pump casing, an inlet port in said pump casing, an outlet port spaced from said inlet port along said casing, chimney means within said casing and extending from the region of said outlet to the region of said inlet, means for supplying pumping vapors to said chimney means, annularly arranged ejector nozzle means disposed about said chimney means in communicating relation with said chimney means and arranged to receive pumping vapors from said chimney means and to dischareg said vapors in a direction away from said inlet, and diffuser means annularly arranged around said chimney means to receive vapors from said ejector nozzle means and to discharge said vapors in the region of said outlet, said diffuser means being constructed and arranged with an upper portion thereof bridging the space between said casing and said chimney means around the circumferential extent of said chimney means, said upper portion being marginally secured to said casing and to said chimney means, the remainder of said diffuser means consisting of relatively thin difiuser tube elements of heat-conducting material, said difiuser tube elements being dependent from said marginally secured upper portion and being spaced from said casing and said chimney means throughout the extent or" said elements downwardly from said upper portion, said elements being of generally uniform thickness throughout the downward extent of said elements, said elements being convergent for a substantial distance downwardly from said upper portion and thence divergent to the lower end of said elements.

3. A high vacuum diifusion pump comprising, in combination, wall means forming a pump chamber having an inlet and an outlet substantially spaced from said inlet along said chamber, chimney means within said chamber and generally coaxial with said chamber, said chimney means extending from the region of said outlet to the region of said inlet, means for supplying pumping vapors to said chimney means, an umbrella jet disposed in the region of said inlet and arranged to receive pumping vapors from said chimney means and discharge said vapors in an annular stream in said chamber in a direction away from said inlet, ejector nozzle means disposed about said chimney means on the outlet side of said umbrella jet and being arranged to receive pumping vapors from said chimney means and to discharge said vapors away from said inlet, said ejector nozzle means comprising an upper disc-like element secured around said chimney means and extending outwardly there-- from with an outer circumferential portion being turned downwardly and inclined outwardly toward said wall means and a lower disc-like element substantially smaller than said upper element spaced below said upper element around said chimney means with an outer circumferential portion of said lower element being turned downwardly and inwardly toward said chimney means, said elements combining to form an annular flared ejector nozzle, and annularly arranged diffuser tube means disposed about said chimney means on the outlet side of said ejector nozzle means and arranged to receive pumping vapors from said ejector nozzle means and discharge said vapors in the region of said outlet, said diffuser tube means being constructed and arranged with the upper end of said diffuser tube means bridging the space between said wall means and said chimney means around the circumferential extent of said chimney means, said dilfuser tube means comprising a metal inner tube wall element and a metal outer tube wall element, said tube wall elements being relatively thin and of generally uniform thickness throughout the extent of said tube wall elements, said outer tube wall element being marginally secured adjacent its upper end around the circumferential extent of said wall means, said inner tube wall element being marginally secured adjacent its upper end around the circumferential extent of said chimney means, the remainder of said elements being dependent from said marginally secured upper ends and spaced from said wall means and said chimney means, said tube wall elements being mutually convergent downwardly for a substantial distance from said upper ends and thence mutually divergent downwardly to the lower ends of said tube wall elements, said tube wall elements combining to form an annular diffusion tube channel for vapors.

KENNETH C. D. HICKMAN.

REFERENCES CITED UNITED STATES PATENTS Name Date Downing et al Oct. 9, 1945 Number

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