US2305947A - Diffusion pump - Google Patents

Description

1942- R. w. ARMSTRONG ET AL 2,305,947

DIFFUSION PUMP Filed Aug. 12, 1942 LIQUIID AIR TRAP fizZezz/ansti 27% I 2950720225 Wflrmsrazzy 7;: K /WQ/IL ZZ 6 y zf.

B in PM 4? Patented Dec. 22, 1942 DIFFUSION PUMP Raymond W. Armstrong and Warren G. Taylor, Chicago, Ill., assignors to Taylor Tubes Inc., Chicago, Ill., a corporation of Illinois Application August 12, 1942, Serial No. 454,564

3 Claims.

initial exhausting is carried out by one or more mechanical exhaust pumps pulling air or other gas from the article being exhausted through the diffusion pump. As soon as the pressure has dropped to several millimeters of mercury, for example about two or three millimeters of mercury, the diffusion pump begins to be effective.

The mechanical pump, while operating, functions as a sink or discharge for the diffusion pump.

Thus, a diffusion pump backed up by a mechanical exhaust pump may be utilized for obtaining vacua of the order of one or two thousandths of a millimeter of mercury. Pumps of this type as a rule have a mercury boiler and jets which impel gas particles. A mercury diffusion pump is provided with a water jacket for condensing mercury vapor. It has beenthe practice to confine the jacketing to parts of the pump only and leave the boiler wall open to air. As a result the construction has been expensive and complicated and considerable heat from the boiler was wasted. Since a diffusion pump of this type can only operate against low pressure differentials it is desirable to have several stages of such pumps. The provision of a single pump having several stages has usually involved complicated glass construction making for great-expense and resulting in fragile structure.

By virtue of this invention, a mercury diffusion pump is provided which has no special water jacket but which may be set in Water. Though the boiler may be in water yet the boiler construction is highly efficient so that all of the heat necessary is retained in the boiler. Furthermore, the structure is simple and may be made by a glass-blower with comparative ease. This invention further provides a simple construction for the pump proper wherein the complexity of glass work usually incident is entirely eliminated.

Referring now to the drawing, Figure l is a sectional elevation of a pump embodying this inven- 1. Figure 3 is a section on line 3-3 of Figure 1. Figure 4 is a section on line 4-4 of Figure 1.

The pump in general comprises a bottom boiler section I above which is disposed the diffuser pump section II the top of which carries an intake section l2 and the bottom of which carries a discharge section 13.

Referring first to boiler section 10, an outer envelope I5 is provided having a reentrant portion 16 terminating in a press Il. Mounted in press I1 is a pair of lead in wires 18 and 19 whose inner ends carry an electric heating element 20. Heating element 20 may be of any type whatsoever and as shown here is generally elongated. Section 10 has a top portion 2| carrying a tubular section 22 within section l0. Tubular section 22 extends downwardly toward press I1 and is turned V back on itself at 23 to provide a reentrant cover portion 24 enclosing heater 20. Between reentrant portion 24 and tubular section 22 an annular chamber 25 is formed within which a quantity of mercury not shown may be disposed.

v The region around section 22 within the outer section Ill forms.an annular chamber 21 which is preferably exhausted to a high vacuum. As is evident from Figure 1, chamber 21 is sealed both from atmosphere and from inner annular chamber 25.

The top portion of tube 22 carries a short cylindrical vapor discharge nozzle 28 extending upwardly away from the boiler. Disposed around discharge nozzle 28 is a fiared foot portion 29 of an elongated diffusing tube 30. Diffusing tube 30 is closed at the upper end 3| and is provided with a bore 32 throughout the length thereof to the closed end. At spaced regions, here shown as two separate regions, a plurality of series of diffusing apertures 33 and 34 respectively may be provided giving access from the inside of the diffusing tube to the outside thereof. Thus, as shown, four apertures 33 are provided at the upper end of the diffusing tube 30 While four apertures 34 are provided at the middle portion of the diffusing tube.

tion. Figure 2 is a section on line 2-2 of Figure The number of apertures is unimportant and may be varied. It will be noted that apertures 33 are substantially larger in size than apertures 34 and this difference is due to the fact that series 33 constitute a first stage while series 34 constitute a second stage.

Around each series of diffusion apertures, there is provided a baffle 35 and 36 respectively of generally cylindrical shape, spaced from tube 30 and extending downwardly toward the boiler.

Diffusing tube 30 has the bottom enlarged portion 29 provided with a plurality of small feet 38 here shown as three in number and consisting of small projections. By virtu of these projections, tube 30 i permitted to rest around nozzle 28 while permitting ready access of the mercury from the outside to the inside of tube 30. The diffusing tube which is loose is steadied and maintained in position by a plurality of springs 40 extending radially from baille 35 to the inside surface of section II of the pump. These springs may be made of any metal such as tungsten and are maintained in position by small protuberances or knobs 4| formed on the outside of baffle 36.

Branchin oil from section II of the pump near the bottom thereof is a side arm 42, having an elbow 43 and thence going up as discharge section l3 of the pump. Section I3 may have a reduced portion 45 to which the auxiliary mechanical pump may be connected directly.

It will be noted that sections l and II of the pump are joined together at portion 2| to form a substantially straight structure that is adapted to stand vertically when in normal use. The upper portion of section II of the pump has a reduced head section 41 having a diameter smal1 er than the diameter of baffle 35 on diffusion tube 30. Thus, the amount of vertical movement of tube 30 within section II is controlled and may be eliminated entirely if desired. Head section 41 of the pump has a sid branch l2 leading therefrom and supporting the intake trap. Thus, as shown here, branch l2 carries at the end thereof a chamber 49 extending downwardly from branch l2 and terminating in a tip 50. has fused therein an intake 52. Tube 52 extends well down into chamber 49 substantially below the level of side branch l2. The entire chamber 49 is adapted to be kept at a very low temperature such as bya liquid air jacket. The pump proper consisting of sections I 0, H and [3 may be disposed in water so that condensation of mercury vapor will be effected. It is understood that leads l8 and I9 are suitably insulated so that water will not be part of any circuit;

The entire structure is preferably made of glass excepting for the heater and possibly springs 40. However, it'is possible to make this pump out of any other suitable material: Over a period of use, any oil, water (frozen other condensates collected in chamber 49 of the trap may be removed by opening tip 50.

It is clear that the boiler proper, consisting of chamber 25 with the space below nozzl 28, is insulated from'the outer envelope I by a vacuum chamber 21. Thus heat leakage is reduced to a minimum.

In the operation of the apparatus the mercury vapor discharged upwardly through the nozzle 28 into the diffusing tube 32 and out of this tube into the pump section H will be condensed pursuant to the heat absorption therefrom by the Water about said section II. The mercury resulting from the condensed vapor collects in the annular trap receiving the enlarged lower end of the tube 30 and thus forms a mercury pool which upon reaching an elevation slightly exceeding the upper end of the nozzle 28 will spill over into the boiler 22, resupplying the boiler with mercury and causing the pump to possess a continuous operating character. This mercury pool within the annular sump on the upper end of the boiler 22 seals the spaces between the supporting feet 38 for the tube 32 to prevent the escape of the mercury vapor from beneath The upper portion 5| of chamber 49 to ice) or the lower end of said tube and causes the discharge of such vapor through the sets of holes 33 and 34. Said spaces at the lower edge of the tube 32 between the feet 38 permit flow of mercury accumulating from the condensation in the pump ll beneath the lower end of the tube 32 and upwardly between the enlarged lower end wall of this tube and the nozzle 28 to ultimately spill over the upper end of this nozzle and into the boiler in the aforesaid manner. The springs 40 disposed upon the bosses 4| projecting radially from the skirt-like baflle 35 on the upper end of the tube 32 impinge with sufil ient force against the wall of the boiler H to frictionally resist endwise movement of the tube 32 whereby the feet 38 are maintained upon the upper end of the boiler. The height of the spaces between such feet and between the lower end of the tube 32 and the upper wall of the boiler 22 is controllable by predetermining the height of the feet.

What is claimed is:

1. In a diffusion mercury pump, a boiler section comprising an outer envelope having a reentrant portion at the bottom thereof, lead-in Wires sealed in said re-entrant portion, an electric heating element connected to said lead-in wires and disposed within said envelope and extending toward the top thereof, a mercury retaining section connected to the top of said boiler section and spaced from said envelope and extending downwardly toward the bottom and having a reentrant portion surrounding said heater, the chambers within and around said mercury containing section being sealed from each other and from atmosphere, said envelope being evacuated to provide thermal insulation between said envelope and said mercury retaining section.

2. A mercury diffusion pump comprising an elongated tube normally adapted to stand in a vertical position, the bottom portion thereof being formed as a boiler section and the remaining portion being formed as a pumping section, said boiler section having a mercury retaining sump and a means for heating said mercury, said pumping section having a separate elongated tube loosely disposed therein, said tube having access to said mercury boiler section and adapted to conduct mercury vapor upwardly within said tube, said tube having its upper end closed and having a plurality of apertures through the wall thereof, baflles carried by said tube for directing mercury vapor issuing through said apertures back toward the bottom of said tube, an intake for said pump at the top of said pump section and an exhaust for said pump at the bottom of said pump section.

3. A' mercury diffusion pump comprising an elongated outer envelope adapted to be disposed in a vertical position during operation, the bottom portion of said envelope forming a, boiler section, said boiler section having a mercury containing chamber spaced from the outer envelope and carried by the top of said boiler section and depending downwardly toward the bottom thereof and having a reentrant portion extending upwardly, said mercury containing chamber being sealed from the outer envelope at the boiler section, lead-in wires sealed in said envelope at the bottom of said boiler section, an electric heating element connected to said lead-in wires and disposed within the reentrant portion of said mercury containing chamber, said mercury containing chamber being surrounded by an annular evacuated chamber of which the outer envelope forms a wall, a nozzle carried by said boiler section at the top thereof for discharging mercury vapor into the pump section, a separate tube having the top end closed disposed over said nozzle section for receiving mercury vapor, said tube having at least one series of apertures through the wall to form a pump stage, a baifle carried by said tube around said series of apertunes for directing rnercury vapor downwardly toward the boiler, said tube being loosely disposed around said nozzle so that condensed mercury may flow into the boiler from around the outside of the bottom of said tube, an air inlet at the top of said pumping section and an air outlet at the bottom of said pumping section.

RAYMOND W. ARMSTRONG. WARREN G. TAYLOR.

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