US2905374A

US2905374A - Diffusion ejector pump

Info

Publication number: US2905374A
Application number: US714176A
Authority: US
Inventors: Thomas L Scatchard
Original assignee: New York Air Brake LLC
Current assignee: New York Air Brake LLC
Priority date: 1958-02-10
Filing date: 1958-02-10
Publication date: 1959-09-22
Anticipated expiration: 1976-09-22

Description

Sept. 22, 1959 T. L. SCATCHARD DIFFUSION EJECTOR PUMP Filed Feb 10, 1958 OOOOOOOQOMQO0000O00OOOOOQWOOOOOOOOOOOQ INVENTOR. ThomasLScatchard A'Horn eys United States Patent DIFFUSION EJECTOR PUMP Thomas L. Scatchard, Philadelphia, Pa., assignor to The lJYew York Air Brake Company, a corporation of New ersey Application February 10, 1958, Serial No. 714,176

3 Claims. (Cl. 230-101) This invention relates .to vapor vacuum pumps and more particularly to diffusion-ejector pumps.

The object of this invention is to provide a diffusionejector pump having a higher throughput (i.e., volume of gas pumped per unit of time multiplied by the pressure of the gas) over a wider pressure range than-similar devices of the prior art while at the same time being more compact. According to the invention, the ejector nozzle comprises an annular opening in a toroidal chamber surrounding the jet chimney which transmits pumping vapors to the diffusion pumping stages. The ejector nozzle discharges into the entrance of an annular diffuser nozzle which is spaced from the ejector nozzle to define an intervening annular entraining area in communication with anannular discharge passage leading from the diffusion pump section. This arrangement of elements results in a compact structure affording a large entraining area for the ejector nozzle.

A further feature of the invention is the provision of means to vary the throat area of both the ejector nozzle and the diffuser nozzle. In prior pumps having fixed throat areas, the minimum pressure which could be established by the pump was limited by the backstreaming of vapor molecules toward the inlet. This is attributable to the fact that as the pressure in the system being evacuated decreased, the rate of backstreaming increased, and when it equaled the throughput of gas, pumping action ceased. This condition could be improved somewhat by varying the energy input to the heater of the vapor boiler as the pressure dropped, but due to the heat capacity of the pump, this procedure was of little help when rapid fluctuations in system pressure were encountered. Furthermore, in this type of pump the dimensions of the throat of the diffuser nozzle should be of the same order of magnitude as the mean free path of the gas molecules at this point. If the throat is too large the pump will have poor fore pressure tolerance; if it is too small the throughput of gas will be reduced. Since the throat area was fixed and since mean free path varies with pressure, the design of the diffuser represented a compromise. In accordance with this invention, the velocity and entraining area of the ejector jet stream can be varied rapidly in accordance with either fore pressure, or inlet pressure, or both, to afford maximum throughput for the prevailing operating conditions.

Referring to the drawing, which is an axial section of a preferred embodiment of the invention, the pump comprises a cylindrical casing 1 having a flanged inlet p assage or port 2 and a plurality of circumferentially spaced outlet passages 3. In the bottom of the casing are located two electrically heated

concentric vapor boilers

4 and 5; the inner boiler 4 feeding a cylindrical jet chimney 6 and the outer boiler 5 feeding a toroidal chamber 7. The chimney 6 is closed by a conical cap 8 and is provided with three longitudinally spaced series of jet openings 9. Associated with each series is a jet skirt 11 formed in the shape of a thin-walled truncated cone and "ice 2 arranged to direct pumping vapors issuing from openings 9 toward the outlet passages 3.

The outer wall of toroidal chamber 7 consists of a fixed portion 12 and a movable portion 13 which slides on chimney 6. Between the two portions of the outer wall is an annular opening 14 which, together with the wall, constitutes an annular ejector nozzle. Aligned with but spaced from annular opening 14 is an encircling annular diffuser nozzle 15 formed by a fixed wall 16 and a movable wall 17 which is guided by ring 18. The annular area 19 between toroidal chamber 7 and nozzle 15 constitutes the entraining area of the ejector nozzle. Communicating with the exit of the diifuser nozzle 15 and with outlet passages 3 is an outlet manifold 21 in which is mounted an annular baflle 22.

A cooling coil 23 surrounds the casing 1. Those pumping vapors which condense on the walls of casing 1 upstream of the ejector nozzle, gravitate to annular trough 24 from which they are returned to inner boiler 4 by return line 25. Those vapors condensing downstream of this nozzle accumulate in manifold 21 and in the space between toroidal chamber 7 and easing 1 and are returned to the outer boiler 5 by

return lines

26 and 27.

The movable walls of both the ejector nozzle 14 and the diffuser nozzle 15 are actuated by

electric motors

28 and 28 through

lead screws

29, 2 9, 31 and 31'. Between

motors

28 and 28 and their associated gearing are located transmissions 32 and 32' which, depending on the type of control desired, can transmit power to either or both lead screws. In this way, the throat areas of the two nozzles can be varied simultaneously or individually.

In operation, gas molecules from the system being evacuated will enter inlet passage 2, and diffuse through the vapor jet streams issuing from openings 9 and skirts 11. The vapor molecules will condense on the cooled walls of housing 1 and be returned to inner boiler 4. The gas molecules, on the other hand, will be directed to the annular entraining area 19 of the ejector nozzle 14. The vapors issuing from annular ejector nozzle 14 will entrap the gas molecules and carry them through the diffuser nozzle 15 to outlet manifold 21 from whence they will be withdrawn by a fore pump through outlet passages 3. The vapors from the ejector nozzle which condense on the walls of the diffuser nozzle 15 and manifold 21 will be returned to the outer boiler 5. The dual boiler and condensate return system makes it possible to use two different oils or to use the same oil at two different pressures. In this way, optimum operating conditions can be closely approximated.

The electric motors 28 and 28' are controlled by a circuit which responds to changes in inlet pressure. When this pressure is high, the motors are operated to reduce the throat areas of

nozzles

14 and 15 and thus provide a high velocity jet capable of producing a high throughput at this pressure. As the inlet pressure decreases, the motors will operate in the reverse direction to increase the areas of the two throats and thus increase the volume of gas being pumped. The net result is that the throughput is maintained substantially constant over a large range of pressures.

In lieu of this inlet pressure control, the motors could be controlled in accordance with changes in fore pressure. As in the previous case, the throat areas would be varied in inverse relation to the pressure. A combined fore pressure and inlet pressure control could also be used.

As stated previously, the drawing and description relate only to a preferred embodiment of the invention. Since many changes can be made in this embodiment without departing from the inventive idea, the following claims should provide the sole measure of the scope of the invention.

What is claimed is:

1. A diffusion-ejector pump comprising a cylindrical casing; two concentricvapor boilers located at one end of the casing; an inlet port formed in the casing at its opposite end; a cylindrical jet chimney-connectedwith the inner boiler; at least one difiusion. pump'nozzle fed by the chimney and arranged to discharge pumping'vapors in a direction away from the inlet port; a housing defining a toroidal chamber surrounding the chimney and connected with the outer boiler, said chamber being located downstream of the diffusion pump nozzle; an encircling opening in the outer periphery of the housing,

issuing from the diffusion pump nozzles and the annular ejector nozzle may condense; a first condensate drain located in thecasing upstream of the annular ejector nozzle and connected with the inner boiler for collecting and returning to that boiler those vapors which condense on the cooled casing; and a second condensate drain located downstream of the annular ejector nozzle and connected with the outer boiler for collecting and returning to that boiler those vapors which condense on the cooled diffuser nozzle.

2. The diffusion-ejector pump defined in claim 1 in which the housing defining the toroidal chamber includes a movable wall which is shiftable in opposite directions to vary the throat area of the annular ejector nozzle; in which the annular difiuser nozzle includes a movable wall which is shiftable in opposite directions to vary the throat area of the diifuser nozzle; and including actuating means connected with the movable housing wall for shifting it in said opposite directions, and actuating means connected with the movable diffuser wall for shifting it in said opposite directions.

3. A diffusion-ejector pump comprising a casing having an inlet and an outlet; a jet chimney located within and spaced from the casing; at least one diffusion pump nozzle located downstream of the inlet and arranged to direct vapors supplied by the chimney toward the outlet; a pumping vapor boiler connected with the chimney; a housing defining a toroidal chamber surrounding the chimney and located downstream-of the diflfusion pump nozzle; an auxiliary boiler connected with the toroidal chamber; an encircling opening in the outer'periphery of the housing, said opening and the walls of the housing cooperating to form an annular ejector nozzle; an annular difiuser nozzle encircling theejector nozzle, the entrance of the diffuser nozzle being aligned with but spaced from the ejector nozzle to define an intervening annular entraining area; and an outlet manifold connected with the exit of the diiiuser nozzle and with the outlet.

References Cited in the file of this patent UNITED STATES PATENTS 2,361,245 Stallmann n. Oct. 24, 1944