US3697195A

US3697195A - Means for restricting vapor backstreaming in a diffusion pump

Info

Publication number: US3697195A
Application number: US22896A
Authority: US
Inventors: Frederick R Johnson; David R Palmer
Original assignee: General Electric Co
Current assignee: RCA Licensing Corp
Priority date: 1970-03-26
Filing date: 1970-03-26
Publication date: 1972-10-10
Anticipated expiration: 1989-10-10

Abstract

For use with a diffusion pump having an inlet connectable to an enclosure sought to be evacuated by the pump, an outlet, and means including a liquid chamber between the inlet and the outlet and means for vaporizing the liquid, the present invention provides improved means for restricting backstreaming of vapors of the liquid from the chamber and into the enclosure. Basically, the improved means comprises pivotally mounted baffle means positionable between the chamber and the enclosure and being pivotable between a first position permitting substantially free flow of fluid between the enclosure and the chamber and a second position substantially restricting flow of fluid between the chamber and the enclosure.

Description

United States Patent Johnson et al.

[ MEANS FOR RESTRICTING VAPOR BACKSTREAMING IN A DIFFUSION PUMP [72] Inventors: Frederick R. Johnson, Chittenango;

David R. Palmer, Liverpool, both of NY.

[73] Assignee: General Electric-Company- [22] Filed: March 26, 1970 [21] Appl. No.: 22,896

[52] US. Cl ..417/154, 417/190 [51] Int. Cl ..F04f 9/08, F04f 5/48 [58] Field of Search ..4l7/l54,190,191, 152,153

[56] References Cited UNITED STATES PATENTS 1,782,310 11/1930 Overstreet ..417/191 2,078,788 4/1937 Bancroft ..417/154 3,460,747 8/1969 Green et al. ..417/191 X FOREIGN PATENTS OR APPLICATIONS [451 Oct. 10, 1972 2/1954 Germany ..417/l52 12/1958 Germany ..417/154 ABSTRACT For use with a diffusion pump having an inlet connectable to an enclosure sought to be evacuated by the pump, an outlet, and means including a liquid chamber between the inlet and the outlet and means for vaporizing the liquid, the present invention provides improved means for restricting backstreaming of vapors of the liquid from the chamber and into the enclosure. Basically, the improved means comprises pivotally mounted baffle means positionable between the chamber and the enclosure and being pivotable between a first position permitting substantially free flow of fluid between the enclosure and the chamber and a second position substantially restricting flow of fluid between the chamber and the enclosure.

3 Claims, 3 Drawing Figures MEANS FOR RESTRICTING VAPOR BACKSTREAMING IN A DIFFUSION PUMP BACKGROUND OF THE INVENTION This invention relates generally to vacuum pumps and, more particularly, to means for restricting the backstreaming of vapor from a diffusion pump toward the enclosure sought to be evacuated by the pump.

Backstreaming is one of the more bothersome problems encountered when using vacuum pumps of the diffusion-type. Backstreaming vapor from the pumping fluid, usually oil or mercury, can contaminate the enclosure sought to be evacuated and cause serious problems; e.g., when high voltage apparatus is to be operated within the enclosure or when high purity ion sources are to'be operated within the enclosure, as is, of course, the case with an electronic vacuum tube, such as the cathode ray tube that is employed as the picture tube in a television receiver.

I-Ieretofore, various forms of fixed baffle means have been positioned between the pump inlet and the enclosure to intercept the backstreaming vapor and restrict its fiow from the pump to the enclosure. These prior-art fixed baffle means have been most elaborate and consequently quite expensive in their construction. U.S. Pat. No. 3,454,214 illustrates a typical version of such intricate prior-art fixed baffle means.

SUMMARY OF THE INVENTION The present invention provides improved means for restricting vapor backstreaming in a diffusion-type vacuum pump which are greatly simplified and reduced in cost when compared with the aforedescribed priorart means that have been provided previously for this purpose.

Basically, the improved means of the present invention comprises pivotally mounted baffle means positionable between the pumps liquid chamber and the enclosure sought to be evacuated by the pump and being pivotable between a first position permitting substantially free flow of fluid between the enclosure and the chamber and a second position substantially restricting flow of fluid between the chamber and the enclosure.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is illustrated in the accompanying drawings, wherein:

FIG. 1 is a somewhat schematic, partly sectioned and broken, elevational view of a diffusion-type vacuum pump employing a presently preferred from of the present invention;

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1; and

FIG. 3 is a simplified, schematic wiring diagram of the electrical control circuit utilized with the mechanism illustrated in FIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, and particularly to FIGS. 1 and 2 thereof, there is illustrated a typical diffusion-type vacuum pump modified and equipped with a presently preferred form of the improved means that are provided in accordance with the present invention.

As shown in FIGS. 1 and 2, the pump 10 comprises a generally vertically-arranged hollow cylindrical casing 11 which is closed at its lower end and has an open, flanged upper end that comprises the pump inlet 12. And, as shown in FIG. 1, the pump 10 is provided with a baffled outlet 13 comprising a generally elbowshaped pipe section 14 which has one of its ends 15 fixed by means such as welding to an opening provided in the lower portion of the vertical sidewall of the pump casing 11 and has its other end 16 extended generally upward.

The bottom of the pump casing 11 is subdivided into two parts, including an upper portion forming a liquid chamber or reservoir 17 for the pumping fluid, such as oil or mercury or the like, which is conventionally employed in a diffusion-type pump, and a lower portion 18 which houses heater means, such as a resistance type electric heating element 19 that is disposed beneath the liquid chamber 17, and, when energized, provides sufficient heat to cause the liquid contained within the chamber or reservoir 17 to vaporize and rise upwardly through a generally vertically arranged hollow cylindrical lower stack 20 that is provided within the pump casing 11. The electrical leads 21 and 22 for the heating element 19 are insulated from but extend outwardly through'the wall of the pump casing 11 for connection across a main source of, electric power in a well-known manner by means not shown.

A lower jet-forming nozzle 23 has a truncated cone shape and is disposed within the pump casing l 1 above the upper end of the lower stack 20. An upper stack 24 is also provided within the pump casing 11 and leads the pumping vapor upwardly from the top of the lower nozzle 23 to an upper nozzle 25 mounted within the upper portion of the pump casing 11. The pumping vapor ascends upwardly through the upper stack 24 with a portion being formed into a jet by the lower nozzle 23 and the remainder being ejected as a jet from the upper nozzle 25. The general configuration and direction of the jet is indicated by dashed lines 26, while the path of the backstreaming vapor is indicated by arrows 27.

The vapor backstreaming restricting means provided include a generally conventional lower annular louvered screen 28, which has the general configuration of a truncated cone and slopes downwardly toward the wall of the pump casing 11 such that condensed pumping fluid will flow by gravity to the wall and downwardly back toward the reservoir 17. While employing the conventional fixed backstream restricting means 28 adjacent the lower nozzle 23, it has been found, in accordance with the present invention, that the functions of the elaborate fixed means (not shown but generally similar to those described in the aforementioned U.S. Pat. No. 3,452,214) which have heretofore been provided adjacent the upper noule 25 can be more economically and satisfactorily performed by substituting therefor improved means of the present invention, generally designated 30.

As best illustrated in FIGS. 1 and 2, the improved means 30 of the present invention basically comprises pivoted baffle means 31 positionable between the liquid chamber 17 and the enclosure 32 (the envelope of a cathode ray tube as shown in FIG. I) sought to be evacuated by the pump 10, and being pivotable between a first position (shown in solid lines in FIG. 1)

permitting substantially free flow of fluid between the enclosure 32 and the chamber 17 and a second position (shown in dotted lines in FIG. 1) substantially restricting flow of fluid between the chamber 17 and the enclosure 32. In the illustrated presently preferred form, the pivoted baffle means 31 comprises a generally discshaped baffle 33 that is pivotally mounted on an axle 34 mounted within a first flanged spool piece member 35 which has its lower end connected by bolts 36 and sealed by an O-ring 37 to the flanged top of the pump inlet 12. This baffle-carrying first spool piece member 35 is also provided with an electro-magnet 38 that is mounted on the inner wall thereof with its

electrical leads

39 and 40 insulated from but extending outwardly through the wall of the first spool piece member 35 for connection across lines L, and 1. of an electric power source that is employed to control the improved bafile means 31 provided by the present invention, as shown in FIG. 3.

In addition, a second flanged spool piece member 41 is connected by more bolts 42 and sealed by another ring 43 to the flanged top of the first spool piece member 35. This second flanged spool piece member 41 has conduit means comprising a curved hollow tube 44 mounted in its wall in a fluid-tight relationship and has a first or inner end 45 which extends downwardly and is aligned over one end of the pivotally-mounted baffle-disc 33 and a second or outer end 46 which extends outwardly through the wall of the second spool piece member 41 and is provided with a normallyclosed solenoid valve 47, which, thus, controls the admission of air via the tube 44 and into the second spool piece member 41. Clamp means 48 and a seal 49 are provided for connecting the open end of the enclosure 32 to be evacuated to the top flange of the second spool piece member 41. Electrical leads 50 and 51 from the solenoid 47' of the air inlet-controlling solenoid valve 47 are connected across the lines L and L of the control means power source as shown in FIG. 3.

As further shown in the wiring diagram of FIG. 3, the solenoid 47' for the valve 47 that is provided at the outer end 46 of the air inlet tube 44 and the electromagnet 38 are connected in electrical parallel across the lines L and 1. of the control means electric power source.

In use of the present invention, the conventional pump is first modified by respectively connecting and sealing the first spool piece member 35 atop the flanged inlet of the pump casing 12 and the second spool piece member 41 atop the first spool piece member 35, as shown in FIG. 1. Then, the open end of the enclosure 32 to be evacuated by the pump 10 is connected and sealed atop the top flange of the second spool piece member 41. Next, a manual switch 52 (FIG. 3) is closed. Then, the pump 10 is actuated by unshown conventional means to evacuate the enclosure 32. At this time, the solenoid 47' for the normallyclosed air inlet valve 47 and the electromagnet 38 are both de-energized, and gravity acts upon a weight 53 that is fastened to the bottom of the opposite end of the baffle-disc 33 to move the pivoted baffle means 31 to its first or open position as shown in solid lines in FIG. 1. This first position permits substantially free flow of fluid through the pump inlet 12 between the enclosure 32 and the pumping liquid containing chamber or reservoir 17. Thus, the weight 53 biases or yieldably urges the pivotally mounted baffle means 31 toward its first or open" position.

Things will remain in this condition until the expiration of a pre-determined period of time, whereupon a normally-open timer switch 54 (FIG. 3), which is connected in electrical series with the manual switch 52 ahead of the electrically paralleled air inlet valve solenoid 47' and electro-magnet 38, will be operated to close and thus to energize the solenoid 47' for the air inlet valve 47 and to energize the electromagnet 38. At this time, the energization of the solenoid 47' opens the normally-closed air inlet valve 47, directing a flow of air at atmospheric pressure into the vacuumed

spool pieces

35 and 41 and onto the top of the end of the baffle-disc 33 which the inner end 45 of the tube 44 overlies. This, in turn, overcomes the bias of the weight 53 and pivots the weight-carrying opposite end of the baffle-disc 33 and magnet-sensitive means 55 carried atop it into contact with the now-energized electro-magnet 38 to thus pivot and hold the pivotally mounted battle means 31 in its second or closed position (shown in dotted lines in FIG. 1) wherein it serves to substantially block or restrict the flow of hot fluid vapors of the liquid from the chamber or reservoir 17 through the inlet 12 of the pump 10 and into the enclosure 32 sought to be evacuated by the pump 10. Thus, the air inlet conduit or tube 44 and the air inlet solenoid control valve 47 provide counter-biasing means for overcoming the yieldable urging (counter-clockwise as shown in FIG. 1) provided to the pivoted baffle means 31 by the weight 53 and for moving the baffle means 31 toward (clockwise as seen in FIG. 1) its second position, and the electro-magnet 38 cooperates with the magnet-sensitive means 55 to provide holding means for holding the pivotable baffle means 31 in its second position.

The apparatus will remain in this latter condition until the timer switch 54 is reset and, hence, reopened.

It should be apparent to those skilled in the art that while there has been described what, at the present, is considered to be the preferred embodiment of this invention in accordance with the Patent Statutes, changes may be made in the disclosed apparatus without actually departing from the true spirit and scope of this invention.

What is claimed is:

1. For use with a diffusion pump having an inlet connectable to an enclosure sought to be evacuated by the pump, an outlet, and means including a liquid chamber between the inlet and the outlet and means for vaporizing the liquid, improved means backstreaming restricting back-streaming of vapors of the liquid from the chamber and into the enclosure upon cessation of evacuation, comprising:

a. pivotally mounted baffle means;

b. said baffle means being positionable between the chamber and the enclosure and being pivotable between a first position permitting substantially free flow of fluid between the enclosure and the chamber and a second position substantially restricting flow of fluid between the chamber and the enclosure;

c. duct means for introducing fluid into the enclosure, said duct means being formed to direct incoming fluid against said baffle means for urging said baffle means toward said second position;

d. biasing means for yieldably urging said baffle means toward said first position; and

e. holding means comprising electro-magnet means positionable between the pump inlet and the enclosure for holding said baffle means in said second position.

2. The invention of claim 1, wherein said electromagnet means is operable to engage magnet-sensitive means carried by said baffle means to hold said baffle means in said second position.

3. For use with a diffusion pump having an inlet connectable to an enclosure sought to be evacuated by the pump, an outlet, and means including a liquid chamber between the inlet and the outlet and means for vaporizing the liquid, improved means for restricting backstreaming of vapors of the liquid from the chamber and into the enclosure upon cessation of evacuation, comprising:

a. pivotally mounted baffle means;

. biasing means comprising weight means carried by said baffle means for yieldably urging said baffle means toward said first position;

holding means comprising electro-magnet means operable to hold said baffle means in said second position;

counterbiasing means comprising a hollow tube having a first end aligned over said pivotally mounted baffle means for directing a stream of fluid against said baffle means to overcome the yieldable urging of said biasing means and move said baffle means toward said second position and a second end for admitting the fluid to form the stream and including electrically-operated valve means; and

. control means for controlling said electrically-

Claims

1. For use with a diffusion pump having an inlet connectable to an enclosure sought to be evacuated by the pump, an outlet, and means including a liquid chamber between the inlet and the outlet and means for vaporizing the liquid, improved means backstreaming restricting back-streaming of vapors of the liquid from the chamber and into the enclosure upon cessation of evacuation, comprising: a. pivotally mounted baffle means; b. said baffle means being positionable between the chamber and the enclosure and being pivotable between a first position permitting substantially free flow of fluid between the enclosure and the chamber and a second position substantially restricting flow of fluid between the chamber and the enclosure; c. duct means for introducing fluid into the enclosure, said duct means being formed to direct incoming fluid against said baffle means for urging said baffle means toward said second position; d. biasing means for yieldably urging said baffle means toward said first position; and e. holding means comprising electro-magnet means positionable between the pump inlet and the enclosure for holding said baffle means in said second position.

2. The invention of claim 1, wherein said electro-magnet means is operable to engage magnet-sensitive means carried by said baffle means to hold said baffle means in said second position.

3. For use with a diffusion pump having an inlet connectable to an enclosure sought to be evacuated by the pump, an outlet, and means including a liquid chamber between the inlet and the outlet and means for vaporizing the liquid, improved means for restricting backstreaming of vapors of the liquid from the chamber and into the enclosure upon cessation of evacuation, comprising: a. pivotally mounted baffle means; b. said baffle means being positionable between the chamber and the enclosure and being pivotable between a first position permitting substantially free flow of fluid between the enclosure and the chamber and a second position substantially restricting flow of fluid between the chamber and the enclosure; c. biasing means comprising weight means carried by said baffle means for yieldably urging said baffle means toward said first position; d. holding means comprising electro-magnet means operable to hold said baffle means in said second position; e. counter-biasing means comprising a hollow tube having a first end aligned over said pivotally mounted baffle means for dIrecting a stream of fluid against said baffle means to overcome the yieldable urging of said biasing means and move said baffle means toward said second position and a second end for admitting the fluid to form the stream and including electrically-operated valve means; and f. control means for controlling said electrically-operated valve means and said electro-magnet means.