Seat structure for gate valves

A non-floating seat structure for an expanding gate valve in which a seat ring is pressed within a body recess and a sealing member is inserted in a groove between a rear face of the seat ring and an opposed wall defining the recess to form a fluid-tight barrier. The groove for the sealing member is of a generally rectangular cross-section and is formed by a counterbore in the valve body and a rearwardly extending inner lip on the seat ring which abuts the recess wall when the seat ring is pressed within the body recess.

BACKGROUND OF THE INVENTION 
U.S. Pat. No. 3,929,316 dated Dec. 30, 1975 and entitled "Non-Floating Seat 
Structure for Expanding Gate Valves" shows an expanded gate valve having a 
valve body with annular recesses in which annular seats are pressed. An 
annular seal is positioned within facing aligned grooves in the back face 
of the seat rings and the opposed recess walls with the seal being of a 
cross-sectional area before insertion slightly larger than the 
cross-sectional area of the two opposed grooves thereby compressing the 
seals when the seals are pressed into position. This arrangement provides 
a fluid-tight barrier to fluid pressure tending to seep behind the seats 
and float or move the seats toward the gate. The arrangement shown in the 
above mentioned patent has functioned in a satisfactory manner but it is 
sometimes difficult and costly to machine the annular grooves in the valve 
body as limited space particularly in small diameter valves is provided 
for the machining of the annular grooves in the recess walls from the 
valve chamber. 
DESCRIPTION OF THE PRESENT INVENTION 
The present invention is directed to an improvement in which the body 
recesses facing the valve chamber and extending about the flow passages 
are each defined by a pair of stepped counterbores having different 
diameters and a seat ring fitting within the stepped counterbores. The 
seat ring has an inner extension or lip extending from the rear face of 
the seat ring with the inner periphery thereof forming a smooth 
continuation of the flow passage and the outer periphery thereof defining 
the inner side of an annular groove in the seat ring. The groove in the 
seat ring and the lip extending from the rear face are in axial alignment 
with the small diameter counterbore in the valve body. The walls defining 
the small diameter counterbore and the groove in the seat ring form an 
annular pocket of a rectangular cross-section. A resilient seal of a 
generally rectangular cross-section is positioned and compressed within 
the pocket to fill the entire cross-sectional area of the pocket to form a 
fluid-tight barrier in the same manner as shown in the above identified 
U.S. Pat. No. 3,929,316. The valve body is easily machined to form the 
stepped counterbores about each of the flow passages at the valve chamber 
in a minimum of time. The above arrangement is particularly adapted for 
expanding gate valves designed for high pressures, such as 20,000 psi for 
example.

Referring now to the drawings for a better understanding of the invention, 
a gate valve structure generally indicated at 10 includes a valve body 
generally designated 12 having a valve chamber 14 therein. An inlet flow 
passage 16 and an outlet flow passage 18 communicate with valve chamber 
14. Flanges 20 on the ends of valve body 12 may be suitably connected to a 
pipeline or other fluid system as is well known in the art. A bonnet 
indicated at 22 has a lower flange 24 which is secured by suitable studs 
26 to the upper end of body 12. 
An expanding gate valve assembly is generally indicated at 30 and is 
mounted for movement between open and closed positions relative to flow 
passages 16 and 18. Gate valve assembly 30 includes a gate element 32 and 
a complementary gate segment 34. Gate element 32 has a concave V-shaped 
back face and segment 34 has a complementary convex V-shaped back face 
fitting within the V-shaped face of gate element 32. A spring 36 
continuously urges segment 34 and gate element 32 toward a collapsed or 
retracted position. Suitable ports are arranged in gate element 32 and 
gate segment 34 for alignment with flow passages 16 and 18 in the open 
position. 
An upper operating valve stem 40 has a threaded portion which is engaged by 
a handwheel 42. The upper end of gate element 32 has a threaded extension 
42 thereon and a key 44 on the end of stem 40 fits in a longitudinal slot 
on extension 42. A cap 46 which receives the end of operating stem 40 is 
threaded on extension 42 to connect stem 40 to gate element 32. 
Mounted adjacent the lower end of gate assembly 30 is a pilot or balancing 
stem 48. Stem 48 is connected to the lower end of gate element 32 by a cap 
50 in a manner similar to the connection of upper operating stem 40. Stems 
40 and 48 are of substantially the same cross-sectional area so that the 
areas of gate assembly 30 exposed to fluid pressure adjacent stems 40 and 
48 are equal. Fluid pressure in chamber 14 above and below gate assembly 
30 are therefore equalized and gate assembly 30 is hydraulically balanced. 
For further details of gate assembly 30 reference is made to the above 
mentioned U.S. Pat. No. 3,929,316 dated Dec. 30, 1975, the entire 
disclosure of which is incorporated by this reference. 
As shown in FIGS. 2 and 3, valve body 12 has an annular recess about flow 
passage 16 which faces valve chamber 14 and is formed by small and large 
diameter stepped counterbores about flow passage 16. The small diameter 
counterbore defines a rear end wall 52 and an outer intermediate annular 
wall 54 extending in perpendicular relation to rear end wall 52. The large 
diameter counterbore defines an intermediate end wall 55 and an outer 
annular wall 56 extending in a perpendicular relation to intermediate end 
wall 55. A seat ring is indicated generally at 58 and has an inner 
peripheral surface 60 and an outer peripheral surface 62. Seat ring 58 has 
a front face 64 adapted to contact gate segment 30 and a rear face 66. 
Extending from rear face 66 is an annular extension or lip 68 having an 
outer peripheral surface 70. An annular groove 72 is formed in rear face 
66 adjacent lip 68 and is defined by an outer side 74, an inner side 
formed by surface 70, and an end wall 76. 
A seal generally indicated 80 has a generally rectangular cross-section 
defined by opposed end surfaces 82 and respective inner and outer 
peripheral surfaces 84 and 86. Seal 80 has a width "W" and a thickness 
"T". A generally rectangular pocket is formed by groove 72 and the small 
diameter counterbore when seat ring 58 is pressed within the recess with 
lip 68 abutting the adjacent rear end wall 52. The pocket is defined by 
rear end wall 52, outer peripheral surface 70 of lip 68, end wall 76, side 
74, and annular wall 54 aligned with side 74. Before insertion of seal 80 
within the rectangular pocket, the width "W" of seal 80 is greater than 
the depth "D" of the pocket with the proportions being such to permit 
compression of seal 80 without buckling but yet adequate to allow seal 80 
to fill in substantially the entire void space in the pocket. Effective 
results have been obtained with "W" being between around 105.degree. and 
130.degree. of the depth "D". The thickness "T" of seal 80 is less than 
the thickness of T1 of the pocket and satisfactory results have been 
obtained with thickness "T" being around 70% to 90% of thickness T1. For 
good results, it would be desirable that seal 80 fill at least around 80% 
of the total cross-sectional area of the generally rectangular pocket 
while 100% would be optimum, but it is very difficult to obtain 100% 
without a portion of seal 80 flowing between the abutting surfaces of lip 
68 and rear end face 52. Highly effective results have been obtained with 
90% of the total cross-sectional area of the pocket being filled with seal 
80. 
Upstream seat ring 58 has been described in detail. A downstream seat ring 
is indicated at 58A and downstream seat ring 58A is generally identical to 
upstream seat ring 58. 
When gate assembly 30 is in a closed position and substantial upstream 
pressure is provided it is very common for a leakage path to occur between 
gate assembly 30 and the upstream seat. Since seal 80 provides a 
fluid-tight barrier, only a limited portion of the entire back face 66 of 
upstream seat ring 58 is exposed to flow line pressure and upstream seat 
ring 58 is easily held in position without moving or floating outwardly 
toward gate segment 34. The recess receiving seat ring 58 is formed by 
small and large diameter counterbores which are easily made from inside 
flow passage 16 and define with groove 72 and lip 68 an enclosed 
rectangular pocket for seal 80.