Compact gate valve

This invention relates to a double-disc gate valve which is compact, comparatively simple to construct, and capable of maintaining high closing pressures on the valve discs with low frictional forces. The valve casing includes axially aligned ports. Mounted in the casing is a sealed chamber which is pivotable transversely of the axis of the ports. The chamber contains the levers for moving the valve discs axially, and an actuator for the levers. When an external drive means pivots the chamber to a position where the discs are between the ports and axially aligned therewith, the actuator for the levers is energized to move the discs into sealing engagement with the ports.

This invention relates generally to gate valves and more particularly to 
gate valves for use with corrosive and/or toxic gases. Such valves 
commonly include a valve disc assembly which is lowered vertically to 
bring the valve discs into register with the valve ports and then moved 
horizontally to close the ports. Two such valves designed for controlling 
the flow of gaseous uranium hexafluoride (UF.sub.6) are described in the 
following: U.S. Pat. No. 2,520,364 to Hobbs, and U.S. Pat. No. 3,815,868 
to Bobo et al. 
Gate valves of the above-mentioned type are subject to several 
shortcomings. For instance, they are comparatively large, complex, and 
expensive. Moreover, the main mechanism of such valves is in direct 
contact with the corrosive and chemically reactive process gas. This means 
that lubrication of the mechanism is not practical and high friction 
forces are present. Furthermore, such valves are poorly suited for use as 
throttling valves. In addition, because these valves are screw-driven, 
they are inherently very slow to operate. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of this invention to provide a comparatively 
simple and small gate valve which is fast-acting but requires only 
relatively low actuating forces. 
It is another object to provide a gate valve having some components which 
are exposed to the process environment but which operate without sliding 
metal-to-metal contact. 
It is another object to provide a gate valve which is comparatively well 
adapted for use as a throttling valve. 
The invention can be summarized as follows: 
A gate valve comprising: A casing enclosing annular seating surfaces 
defining first and second ports having a common axis; a gate assembly 
pivotally mounted in said casing for movement in a plane transverse of 
said axis, said assembly including: 
A. a pair of valve discs having frontal sealing surfaces for respectively 
engaging said seating surfaces to close said ports; 
B. levers respectively connected to said discs; 
C. means for operating said levers to move said discs along said axis to 
open and close said ports; and 
D. a housing isolating said levers and said means from said casing, said 
housing including flexible sealing means respectively connected to said 
discs for accommodating movement of said discs along said axis.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The invention will be illustrated herein chiefly in terms of a double-disc 
gate valve designed for use in gaseous UF.sub.6 at an elevated 
temperature. The valve may be composed throughout of conventional 
components. 
Referring to the figures, the new gate valve includes a casing 1. The 
casing enclosed opposed annular seating surfaces 3 and 5 which have a 
common axis A and which defines valve ports 7 and 9. Mounted in the casing 
is a gate assembly which includes a pair of spaced, back-to-back valve 
discs 13 and 15; three generally L-shaped lever-arms 17, 19 and 21; means 
23 for effecting movement of said discs along said axis by means of the 
levers; and a housing 25 isolating the levers and the actuating means 23 
from the casing. The housing includes two bellows members 39 and 41. 
The valve discs 13 and 15 carry frontal sealing rings 27 and 29 for 
respectively engaging the seats 3 and 5 to close the valve ports. As 
shown, the shorter legs of the levers 19 and 21 are pivotally connected to 
spaced lugs 31 on the back of the disc 15, their longer legs being 
similarly connected to spaced extensions 32 and 34 of the frame of the 
actuator means 23. The actuator 23 may comprise a double-acting pneumatic 
or hydraulic cylinder having a piston-driven stem 33. As shown (FIG. 1) 
the lever 17 is connected between arms 19 and 21, with its shorter leg 
pivotally connected to a lug 30 on the back of disc 13 and its longer leg 
similarly connected to the stem 33. The three levers are connected by a 
pin 37, about which they can pivot, or rock. 
As shown, the bellows portions 39 and 41 of the housing 25 are respectively 
connected to the backs of the valve discs to seal the interior of the 
housing from the casing 1 and to permit movement of the discs along axis 
A. Rearward travel of the discs is limited by stops 51 mounted to the 
housing. A typical stop is shown in FIG. 2. Means are provided for 
preventing lateral shifting of the discs during their movement along axis 
A. A typical arrangement for preventing such shifting of disc 15 is 
illustrated in FIG. 2, which shows a pin 53 which is affixed to the rear 
of the disc and is slidably engaged by guide brackets 55 mounted to the 
housing 25. Preferably, each disc is provided with a plurality of such 
arrangements. 
Referring to FIG. 2, the gate assembly is supported near its upper end by 
rotatable, axially aligned shafts 43 and 45, each of which has an end 
affixed to the housing 25 and each of which is supported by bearings 47 
carried by the casing. A thrust bearing 48 also is provided as shown. The 
shaft 45 which is hollow, extends through the casing and a conventional 
shaft seal 46. As shown in FIG. 1, the external end of shaft 45 is 
connected to any suitable operator 49 (FIG. 1) for imparting arcuate 
movement to the shaft to pivot the gate assembly transversely of the axis 
A. More specifically, the means 49 pivots the gate assembly between a 
position where the discs 13 and 15 are respectively aligned with the seats 
3 and 5 and a postion where the discs are remote from the seats. The 
latter position is indicated by dashed lines in FIG. 1. 
As indicated in FIG. 2, shaft 45 is formed with an axial bore for the 
passage of fluid-containing lines 61 which extend from the actuator 23 to 
any suitable external operator therefor (not shown). 
With the valve in the full-open position (gate assembly pivoted to the 
position shown in dashed lines in FIG. 1), process gas flow through the 
ports is unrestricted. The interior of the casing is exposed to the 
corrosive process gas, but the seal 46 prevents outleakage of the gas from 
the casing, whereas the housing 25 (including the bellows 39 and 41) 
isolates the interior of the gate assembly from the gas. Closing of the 
valve is effected by actuating the operator 49 to pivot the gate assembly 
to the position where the sealing rings 27 and 29 are in register with the 
seats 3 and 5. The actuator 23 then is energized to move the upper end of 
the lever 17 away from levers 19 and 21, thus pivoting the three levers 
about pin 37 and moving the valve discs outward to close the valve. The 
acutator remains energized to maintain a selected pressure on the discs 
when closed. Opening of the valve is effected by reversing the actuator 23 
to retract the discs along axis A, and then energizing the operator 49 to 
pivot the gate assembly to the remote position. It will be apparent that, 
if desired, the valve can be employed to throttle the flow by pivoting the 
gate assembly to intermediate positions where it partially overlaps the 
valve ports. 
Where the process gas is UF.sub.6, the valve components that will be in 
contact with the gas are made of materials compatible with the same. For 
example, the discs, casing, housing, and shafts may be formed of 
nickel-plated steel, the seats and bellows, of phosphor bronze; the 
sealing rings, of Teflon; the shaft bearing surfaces, of Teflon; and the 
shaft packing, of Teflon. 
This invention provides important advantages over conventional gate valves. 
For example, sliding between the sealing rings and seats is essentially 
eliminated. All of the sliding bearing surfaces, except the Teflon shaft 
bearing, are isolated from the process gas. The stem seal 46 sees only 
rotary motion. The rockerarm arrangement is comparatively small and is not 
complex, yet it provides a very high leverage factor. Thus, comparatively 
low actuating forces are required to develop high seating forces--e.g., 
seating forces of 600 pounds per inch of seat circumference. The valve 
design ensures comparatively low differential gas loads on the discs, 
since the interior of the valve assembly is always vented to atmospheric 
pressure through the hollow shaft 45. In previous gate valves the zone 
between the discs can at times be at a pressure level higher than 
atmospheric. This means that under certain operating conditions a higher 
differential pressure can exist across a valve disc than would otherwise 
be present. 
It will be apparent to those versed in the art that various modifications 
can be made to the invention as illustrated without departing from the 
scope of the appended claims. One of the outer levers 19 and 21 may be 
omitted, although preferably two such levers are employed to avoid 
applying undesirable torsion and bending forces to the actuator 23 and its 
stem 33. It will be apparent that the stem 33 may be operated by any 
suitable means, such as electrically driven gears, although a pneumatic 
operator is preferred for high temperature environments. If desired, the 
shaft seal 46 may be mounted to the inside wall of the casing.