US2215449A

US2215449A - Gland for vacuum chambers

Info

Publication number: US2215449A
Application number: US289596A
Authority: US
Inventors: Alexander Paul; Barnes Philip Carringten
Original assignee: Pilkington Brothers Ltd
Current assignee: Pilkington Group Ltd
Priority date: 1938-08-24
Filing date: 1939-08-11
Publication date: 1940-09-24
Anticipated expiration: 1957-09-24
Also published as: NL52943C; BE435921A; GB518526A; FR858939A

Description

Sept. 24, 3940. P. ALEXANDER ET AL 2,215,449

sump FOR VACUUM CHAMBERS Filed Aug. 11, 1939 Hal.

E /6 /a v Patented Sept. 24, 1940 UNITED STATES,

PATENT oFFics 2,215,449 I cum) roa vacuum cnmasas Great Britain Application August 11, 1939, Serial No. 289,598

In Great Britain August 24, 1938 7 Claims.

This inventionrelates to vacuum chamber apparatus and has for its object to provide a liquid sealed gland for a member entering the chamber.

The invention *is particularly adapted to glands for movable members such as rotatable shafts.

In the case of chambers with high vacua'it is impracticable to introduce a moving member, or a member which may have to be moved, for instance, for adjustment, in such a way as to avoid leakage, unless a liquid seal is used. IfJnercury is permissible, a mercury seal is practicable, since the height of the seal is only 760 mm. but this height is often inconvenient. Generally, however, for high vacua, mercury is inadmissible, and 1 the only liquid permissible is an oil with negligibly small vapour pressure, such as apiezon oil. The height of a seal of oil, being 35-40 feet, is generally impracticable.

By means of the invention, the height of the g liquid seal in a liquid-sealed gland may be only a few millimetres.

According to the invention an annular U-tube containing the sealing liquid has the space above the liquid in one leg connected to the vacuum 25 chamber and the space above the liquid in the other leg connected to an auxiliary vacuum, the pressure difference between the vacuum in the chamber and the auxiliary vacuum, measured in head of the sealing liquid, being less than the cf fective height of the U-tube.

In the accompanying drawing: Figures land 2 are vertical sections of liquidsealed glands for a member introduced into the vacuum chamber from below, and for amember 35 introduced from above, respectively, and

Figure 3 is a diagrammatic view of a vacuum chamber with gland and pumps.

Referring to Figure-1, the wall of. the vacuum chamber is shown at l, and 2 is the movable 40 member introduced into the chamber. A casing 3, containing the sealing liquid 4, is attached to the Wall E of the vacuum chamber by the tubular member 5. This member has a depending tubular portion 6, which dips into the liquid 4, and surrounds the member 2. The member 2 passes out of the casing 3 through the stufflng box I which may be of any construction used in vacuum practice. The casing 3 and tube 6 this form an annular U-tube, with inner leg 8, connected 50 with the vacuum chamber, and outer leg 9. The

space above the liquid in the outer leg 9 is connected by a pipe it to an auxiliary source of vacuum. In high vacuum apparatus, it is customary to use a preliminary vacuum pump followed by a 55 final pump, the preliminary pump being generally a mechanical-pump, capable of reducing the pressure to about 0.l mm. of mercury, while the final pump is, generally a dispersion pump which may reduce the pressure in the vacuum chamber V to 0.001 mm. or less. Figure 3 shows this arrangement diagrammatically, it being the preliminary pump and I2 the final pump, and the pipe I0 is shown connecting the gland casing 3 with the vacuum side of the preliminary pump H, Under these conditions the pressure in the 10 space 8 above the liquid in the inner leg of the U-tube is, say, 0.001 mm., and that in the space 9 in the outer leg is, say, 0.1 mm. There is thus a pressure diil'erence in the two legs of the U- H tube of only about 0.1 mm. of mercury or about 1.5 mm. of oil, and, if oil be used, the liquid levels in the U-tube are somewhat as shown in the drawing. The auxiliary source of vacuum could be an independent pump, giving a vacuum of, say,

10 mm. of mercury, and then the pressure difference in the two legs of the U-tube would be about 150 mm. of oil, and the dimensions of the gland would still be quite small.

A bathe I3 is fixed to the member 2 above the stufling box 'I to guide away any bubbles oi air g5 which may leak through the stufling box into the outer leg of the U-t'ube. They then rise into the space '9, from which the air is evacuated by the auxiliary source of vacuum through the pipe l0.

'When the preliminary pump ii is connected with the space 9, a vessel H is preferably connected with the casing 3 to withdraw the sealing liquid, and leave a freeconnection from the pipe I0 to the vacuum chamber. Thereby differences I of level in the two legs of the U-tube, due to temporary large differences of vacuum, are avoided.

The upper part of the vessel It is connected to the pipe l0,-by the pipe l5, and the lower part is connected to the bottom of the casing 3 by the pipe Hi. The liquid canthen be withdrawn from 40 the casing 3 to a level below the bottom end of a the tube 8, by lowering the vessel. Then, when the vacuum in the chamber has been reduced to. say, 1 mm. of mercury, the liquid is returned to the casing 3 by raising the vessel It to the posi- 5 tion indicated. Figure 2 shows the liquid-sealed gland applied to a member entering the vacuum chamber from above. The casing 3 has an internal tubular wall i1, forming an annular space to contain tha'liquid, and a bell jar I 8 is fixed to the member 2 and dips into the liquid, thus forming a u-tube with two legs 9 and 9, respectively between the bell jar and the wall I! and between the bell jar and the outer wall of the casing 3. u

In the construction of Figure 2, the U-tube has an efiective height between the top of the wall l1 and the bottom of the bell jar l8 and, to maintain the seal, the auxiliary source of vacuum to which the pipe 10 is connected must be at a pressure, reckoned in head of the sealing liquid, which is above the pressure in the chamber by an amount less than the eifective height of the U-tube. In the construction of Figure 1, the effective height of the U-tube is twice the height of the pipe I0 above the bottom of the tube 6.

The gland may also be used to seal a shaft entering the vacuum chamber horizontally, by connecting the horizontal shalt by bevel gear to a vertically descending shaft. The tubular member 5, of Figure 1, is then extended as an elbow to house the bevel gear and horizontal shaft.

The vessel It may be connected to the casing 3 only by the single pipe [6, and then the vessel,

.when lowered to drain off the oil from the casing, is inverted, so that the space above the oil in the vessel is evacuated by the pump H at the same time as the casing 3.

Having described our invention, We declare that what we claim and-desire to secure by Letters Patent is:

1. In vacuum chamber apparatus comprising a final pump and a backing pump connected in series for exhausting the chamber and a movable member introduced from outside into the chamber, a liquid seal for the: member comprising an annular U-tube containing the sealing liquid of which the inner leg surrounds the mem ber, a passage from the chamber to the space above the liquid in the inner leg, and a connection from the space above the liquid in the outer leg of the U-tube to the connection between the backing and final pumps.

2. In vacuum chamber apparatus comprising a final pump and a backing pump connected in series for exhausting the chamber and a movable member introduced from outside, into the chamber, a liquid seal for the member comprising an annular U-tube consisting of a tube surrounding the member and a casing surrounding the tube, sealing liquid in the casing'both within and without the tube, a stufilng box in the bottom of the casing through which the member is adapted to pass, a passage from the chamber to the space in the tube above the liquid and a connection from the space above the liquid in the casing and outside the tube to the connection between the backing and final pumps.

3. In vacuum chamber apparatus comprising a final pump and a backing pump connected in series for exhausting the chamber and a movable member introduced from outside into the top of the chamber, a liquid seal for the member comprising an annular U-tube, consisting of a tube surrounding the member, a bell-jar fixed to the member and surrounding the tube, and a casing surrounding the bell-jar, sealing liquid in the casing both without the bell-jar and between the bell-jar and the tube, a stufflng box in the top of the casing through which the member is 5. In vacuum chamber apparatus comprising a movable member introduced from outside into the chamber, a liquid seal for the member comprising an annular U-tube containing the sealing liquid of which the inner leg surrounds the member, a passage from the chamber to the space above the liquid in the inner leg, a vacuum pump adapted to maintain a vacuum lower than the vacuum in the chamber by an amount not exceeding the effective height of the U-tube, reckoned in head of the sealing liquid and a connection from the space above the liquid in the outer leg of the U-tube to the vacuum pump.

6. In vacuum chamber apparatus comprising a movable member introduced from outside, into the chamber, a liquid seal for the member comprising an annular U-tube consisting of a tube surrounding the member and a casing surrounding the tube, sealing liquid in the casing both within and without the tube, a stuffing box in the bottom of the casing through which the member is adapted to pass, a passage from the chamber to the space in the tube above the liquid, a vacuum pump adapted to maintain a vacuum lower than the vacuum in the chamber by an amount not exceeding the effective height of the U-tube, reckoned in head of the sealing liquid, and a connection from the space above the liquid in the casing and outside the tube to the vacuum pump.

7. In vacuum chamber apparatus comprising a movable member introduced from outside into the top of the chamber, a liquid seal for the member comprising an annular U-tube, consisting of a tube surrounding the member, a belljar fixed to the member and surrounding the tube and a casing surrounding the bell-jar, sealing liquid in the casing both without the bell-jar and between the bell-jar and the tube, a stufilng box in the top of the casing through which the member is adapted to pass, a passage from the chamber through the tube to the space above the liquid in the bell-jar, a vacuum pump adapted to maintain a vacuum lower than the vacuum in the chamber by an amountnot exceed-= ing the eflective height of the U-tube, reckoned in head of the sealing liquid, and a connection from the space above the liquid in the casing to the vacuum pump.

PAUL ALEXANDER. PHILIP CARRINGTON BARNES;