Expanding gate valve with pneumatic actuator

A piston type pneumatic powered actuator (9) for operating a valve (10) of the expanding gate type wherein velocity of the piston-stem-gate drive train is maintained substantially constant in the latter stage of the actuator stroke. The actuator (9) includes an assembly of dual pistons (61,75) which are adapted to be driven by fluid pressure in one direction to operate the valve but are returned by spring means (66,67) when the fluid pressure is removed. A drive piston (61) directly connected to the actuator stem (23) is nested within a primary piston (75) which is not connected to the actuator stem (23) but moves the drive piston (61) when actuating pneumatic fluid is applied to the actuator (9). A stop (85) affixed to the primary piston (75) is adapted to cooperatively engage the actuator housing (40) to terminate the stroke of the primary piston (75) prior to termination of the stroke of the drive piston (61). An orifice (91) through the primary piston (75 ) allows continuing flow of actuating fluid to the face of the drive piston (61) after the stroke of the primary piston (75) is terminated. Termination of the stroke of the primary piston (75) occurs when fluid communication through the valve is first established.

BACKGROUND OF THE INVENTION 
This invention relates to expanding gate valves and more particularly to an 
expanding gate valve provided with a dual stage pneumatic-powered 
actuator. 
With single stem valves which handle very high pressures, the large forces 
needed to operate the valve preclude the use of any manual means, such as 
a handwheel, and require the provision of an automatic operator. Automatic 
operators are also widely used in applications for operating a valve in 
automatic response to sensing of some changed condition as, for example, 
with safety valves which are incorporated in safety systems. 
Heretofore, the use of fluid-powered actuators with gate valves of the 
expanding gate type has presented many problems. Variances in the sealing 
forces between expanding gate valves, even those of the same kind, usually 
rules out the adaptability of an actuator with a uniform thrust force for 
a variety of valves wherein such variant characteristics are the general 
rule. Also, the very large sealing forces of these valves require a very 
powerful actuator thrust to break the "seal" and such a powerful thrust 
can serously damage the valve components, such as the seal rings or the 
gate and segment members. A very large spring force is also needed to 
return the actuator piston upon release of fluid pressure from the 
actuator and these significantly increase the size, weight and expense of 
the actuator. Nevertheless, the handling of very high fluid pressures of 
20,000 p.s.i. or more, as is characteristic of deep gas and oil wells, has 
made it very desirable that only gate valves of the expanding gate type be 
used, and particularly so in safety valves for very high pressure systems. 
As opposed to hydraulic actuators, pneumatic actuators are often times 
used where quick response times are needed, where reduction of the 
flammability hazard is important, or where pneumatic power is readily 
available. 
In the design of actuators for expanding gate valves, the piston must be 
sized so minimum fluid pressure to the actuator is able to overcome the 
valve's gate drag plus the pressure which acts across the cross section of 
the stem to oppose the actuator thrust. At approximately one third of the 
actuator stroke distance, the gate ports and valve conduct flow passage 
come into communication so that pressurized fluid in the valve body cavity 
is vented to the flow passage. As this happens, both the gate drag and the 
opposing stem force are lost. If the actuator fluid is hydraulic, a small 
displacement of the actuator piston suffices to lower the fluid pressure 
driving the actuator to substantially zero so that the valve completes its 
stroke, as in moving from closed to open position, at a relatively slow 
speed determined by the flow rate of the actuator pressure source fluid 
and the actuator orifice inlet. 
In applications where pneumatic actuators are used to control the operation 
of gate valves, the instant of occurrence of lost gate drag and opposing 
stem face during the actuator stroke allows the actuator fluid, a gas, to 
rapidly expand. Because the gas is compressible, the actuator piston moves 
a distance much greater than the valve stroke before the hydraulic 
actuator pressure is significantly reduced. The result is the connected 
"train" of actuator piston, stem and valve gate assembly moves with such 
greater velocity and momentum as to "slam" against the valve stop which 
causes the rapid expansion and very tight wedging of the gate and segment 
elements of the valve gate assembly in its expanded sealed condition. In 
addition to the likelihood of valve damage, a further disadvantage is that 
a very large force is required to break the "wedge" to permit further 
operation or "fail-safe" operation of the valve. One solution to this 
problem is disclosed in U.S. patent application Ser. No. 568,460, filed 
Jan. 5, 1984 now U.S. Pat. No. 4,535,967, which shows an expanding gate 
valve operated by a piston type pneumatic-powered actuator which includes 
a hydraulic choke means to reduce the "slam" effect. There is, of course, 
the possibility of leakage of hydraulic fluid from the hydraulic choke, 
especially over a long period of time, such that a totally pneumatic 
actuator system may be preferred. The provision of a hydraulic choke means 
also increases the number of parts and the complexity of the actuator. 
Accordingly, it is an object of the invention to provide a simple and 
reliable pneumatic actuator for operation of a gate valve of the 
expandable gate type. 
It is another object to provide a dual piston pneumatic-powered dual piston 
actuator for operation of a gate valve of the expandable gate type wherein 
actuator stem velocity is controlled to substantially constant velocity by 
restricting the flow of actuating fluid to the actuating piston at a time 
during the actuator stroke when the valve gate ports first come into 
communication with the flow passage through the valve. 
A further object is to provide a pneumatic-powered dual stage actuator for 
actuating the control element of a mechanical device wherein actuator stem 
velocity is controlled by sudden restriction of air flow to the actuating 
drive piston means in the latter stage of actuator thrust. 
SUMMARY OF THE INVENTION 
The invention is directed to a dual stage pneumatic actuator for actuation 
of the control element of a mechanical device such as the gate assembly of 
an expanding gate valve. The actuator, which is mounted atop the valve 
housing, comprises an actuator housing defining a piston chamber, a 
primary piston and a secondary drive piston slidably received in the 
housing, and an actuator stem which connects the secondary drive piston to 
the valve gate assembly. The primary piston is not connected to the 
actuator stem but seats loosely atop the secondary drive piston when the 
actuator is in the de-energized condition. The actuator is responsive to a 
source of pneumatic fluid pressure which when applied through an inlet of 
the actuator housing to one side of the pistons drives the actuator stem 
and gate assembly to an operational open or closed position. A spring 
means in the piston chamber continuously urges the piston in the direction 
which opposes the pneumatic pressure. A secondary piston, of smaller 
piston area than the first, is fitted into a piston receiving bore which 
is formed in the fluid receiving face of the first piston. A stop member 
affixed to the primary piston is adapted to cooperably engage the actuator 
housing to limit the length of the primary piston stroke to a lesser 
length than that of the secondary drive piston stroke when pneumatic fluid 
is admitted to the piston chamber. The stop is so located that the stroke 
of the primary piston terminates shortly after fluid communication is 
established between the ports of the gate assembly components and the flow 
passage through the valve. 
A small diameter flow control orifice through the primary piston allows 
continuing flow of actuating fluid to the secondary piston after the 
stroke of the primary piston is terminated. The flow control orifice so 
restricts the flow of actuating fluid acting to drive the actuator stem 
that the actuator stem velocity and associated momentum of the actuator 
stem and valve gate assembly is reduced.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
As shown in FIG. 1, the actuator 9 of this invention is shown mounted to a 
gate valve 10 for controlling the operation fo the valve. The valve 10 
comprises a valve body 11 having a valve chamber 12 therein and inlet and 
outlet flow passages 13, 14 defining a flow way which extends through the 
valve and intersects the valve chamber 12. End flanges 15, each in 
surrounding relation to the flow way, are provided on the valve body to 
accommodate its installation in a flowline. The valve is also provided 
with a bonnet 19 which is bolted atop the valve body 11 by means of bolts 
16 and closes off the valve chamber 12. 
The valve 10 further includes a gate assembly 20 of conventional design 
which is mounted within the valve chamber for sliding movement 
transversely of the flow way to open or close the valve. The gate assembly 
20 includes a gate member 21 and a segment 22. The gate member 21 is 
connected at its upper end to the lower end of a valve stem or actuator 
stem 23 which extends through a central axial bore 24 in the bonnet 19. 
The stem 23 is connected to the gate member 21 so that upon actuation of 
the stem 23 in the axial direction, as will hereinafter be described, the 
gate assembly 20 is movable across the flow way between a first position 
werein the valve is open and a second position wherein the valve is 
closed. In the open position of the valve, not shown, ports 26, 27 in the 
gate and segment members, respectively, are aligned in registry with the 
flow passages 13, 14. Also, as is conventional, the gate member 21 is 
provided with a V-shaped recess which accommodates the wedge shaped 
segment 22, the wedge faces of which conform to the surfaces of the 
V-shaped recess and are in sliding contact therewith. As is well known to 
those skilled in the art, the linear movement of the gate assembly to open 
or close the valve, causes an expansion of the gate assembly in the open 
and closed positions due to relative sliding movement between the gate 
member 21 and the segment 22, the relative sliding movement being induced 
by suitable stop means, such as the surface 28 of the valve end plate 17 
which closes off the valve chamber 12 and which limits the vertical 
movement of the segment 22 relative to the gate member 21 as the gate 
assembly nears its valve open position. A similar stop means adjacent the 
top end of the valve chamber 12 restricts the movement of the segment 
relative to the gate member as the gate assembly nears its valve closed 
position. 
At the inner ends of the flow passages 13, 14, the valve body 11 is 
provided with annular recesses 31, 32, respectively, surrounding the flow 
passages 13, 14 in concentric relation therewith and opening into the 
valve chamber 12. The annular recesses 31, 32 from seat pockets in each of 
which a valve seat ring 33 is inserted. 
For sealing, the gate member 21 is provided with a flat outwardly facing 
sealing surface 34 which is oriented substantially parallel at all times 
to a similar sealing surface 35 on the segment 22 which faces in the 
opposite direction towards the inlet passage 13. When the gate assembly is 
expanded in the open and closed conditions of the valve, the surfaces 34, 
35 establish sealing relationships with the valve seats 33. When in 
transit between the open and closed positions, the gate assembly assumes a 
collapsed condition which is induced by a suitable means (not shown) 
affixed to the sides of the gate and segment members for continuously 
urging these members to a "nested" relationship wherein the respective 
apexes of their inner wedge surfaces are aligned. A suitable mechanism for 
collapsing the gate assembly to its "nested" condition is shown in U.S. 
Pat. No. 4,334,666. 
The gate is connected to the stem 23 by any suitable connection but is 
preferably a low stress stem connection such as shown in U.S. Pat. No. 
3,923,285. 
The stem 23 extends through the bonnet bore 24 and a packing gland assembly 
36 which is mounted in an enlarged diameter portion 24a of the bonnet bore 
24. Annular packing rings 38 of the packing assembly are disposed in the 
bore section 24a and provide fluid-tight sealing between the valve bonnet 
and the valve stem when compressed by the packing adapter 37 which is 
threaded into the enlargement 24a of the bonnet bore 24. The stem packing, 
of course, may be other than shown and may be any packing suitable as a 
valve stem shaft packing. 
The actuator 9 which is used to actuate the gate valve 10 is shown mounted 
atop the valve body 11. The actuator 9 comprises a hollow cylindrical 
housing member 40 of circular cross-section which defines and actuator 
piston chamber 41. The cylindrical housing 40 is comprised of a lower 
hollow cylinder member 40A and an upper inverted cup-like member 40B of 
corresponding diameter. The housing 40 is closed at one end by a circular 
housing end member 42 and the housing members 40A, 40B are joined in 
coaxial relation by bolts 38 through aligned bores in the end member 42 
and the housing members 40A, 40B. The housing end member 42 is formed with 
a central axial bore 43 which receives the upper end of the valve bonnet 
19 in close fluid sealing relation therewith as the actuator is mounted on 
the valve 10. The end member 42 seats on an annular bonnet shoulder 44 
which is formed by a reduction in diameter of the upper end of the bonnet 
19. 
As best shown in FIG. 2, it will be seen that the actuator 9 is secured to 
the top of the valve body 11 by a split ring 57 which is received in an 
external groove 58 formed around the exterior of the bonnet 19 near its 
upper end and clamps against the surface 59 of the actuator housing end 
member 42 which is an inner end wall of the actuator piston chamber 41. In 
addition, one or more keys 60 are fitted into aligned slots in the 
exterior of bonnet 19 and the wall formed in the central axial bore of the 
end member 42 to prevent any relative rotation of the actuator with 
respect to the valve body 11. 
The actuator 9 includes a piston assembly which comprises a primary piston 
75 slidably mounted in the piston chamber 41 and a drive piston 61 which 
is normally disposed in abutting relation to the piston 75 when the 
actuator is in its relaxed condition. The drive piston 61 is threaded onto 
the upper end of an adapter 62, which is in turn threadedly connected to 
the upper end of the actuator stem 23 as an extension of the stem 23. As 
shown, the drive piston 61 is in coaxial alignment with the actuator stem 
23 and is of a diameter which is less than that of the inner diameter of 
the actuator housing 40 for purposes hereinafter explained. 
The piston 61 is biased towards the upper end of the piston chamber 41 by a 
pair of coiled springs 66, 67 which are arranged in sleeved relation to 
one another and around the actuator stem 23 and its adapter extension 62. 
The upper ends of the springs 66, 67 abut the underside of the piston 61 
and the lower ends of the springs abut an annular spring retainer plate 68 
which is seated atop a TEFLON washer 56 and the clamp ring 57 adjacent the 
end member 42. For purposes of reducing the size of the actuator 9, a pair 
of coiled springs rather than a single spring is preferred to continuously 
urge the piston 61 in a direction away from the valve body 10. Since a 
very powerful thrust is required for actuation of a gate valve of the 
expanding type, the actuator 9 is provided with a unique feature for 
reducing the velocity of the actuator stem 23 in the latter stage of an 
actuator stroke. It is to be noted that with the present invention, at 
approximately one third of the way through an actuator stroke, fluid 
communication is established between the ports 26, 27 of the gate assembly 
members and the flow passages 13, 14. There is also an accompanying loss 
of gate drag and the forces opposing the actuator stem stroke such that 
there will be a sudden increase in actuator piston-stem velocity and 
momentum of the piston-stem-gate assembly unless means are provided to 
prevent this happening. 
As a means of reducing actuator stem velocity, the invention incorporates 
another piston, the primary piston 75, which seats loosely atop the drive 
piston 61. The piston 75 is of diameter corresponding substantially to the 
inner diameter of the housing 40 so as to provide for a close sliding fit 
therebetween. Piston rings, or seals 76, are fitted in a circumferential 
groove around the piston 75 to insure a fluid-tight seal between the 
piston 75 and actuator housing 40. The piston 75 is also provided with a 
central axial bore 75A for accommodating a rod-like piston guide 77 which 
extends therethrough and is threadedly connected to the actuator stem 23 
in coaxial alignment therewith. For this purpose the lower end of the 
piston guide 77 is formed with an externally threaded reduced diameter 
portion 77A which is threadedly received in a threaded bore 23A formed in 
the end of the actuator stem 23. The piston 75 is not rigidly connected to 
the guide 77 but is sleeved thereon in fluid-tight relationship 
established by means of an o-ring seal 78 in the central bore through the 
piston 75. The piston guide 77 also extends out of the actuator housing 40 
through a central opening 80 which is formed in the closed upper end of 
the actuator housing member 40B. O-ring seals 81, 82 fitted in the wall of 
the opening 80 establish a fluid-tight seal between the actuator housing 
and the piston guide 77. 
A fluid pressure inlet 71 is provided in the closed end of the housing 
member 40A of the actuator 9 and is formed with internal threads for 
accommodating its connection to a pressure conduit leading to a source of 
pneumatic fluid pressure. As is readily apparent, pneumatic fluid under 
pressure delivered to the piston chamber through the inlet 71 will drive 
the pistons 75 and 61 downwardly against the counterforce of the piston 
springs 66, 67 to where the gate assembly of the valve 10 is moved towards 
the bottom of the valve chamber 12 and is expanded into sealing engagement 
with the valve seats 33 to open the valve. 
In the gate valve 10, the openings 26, 27 in the gate and segment members 
are located near the upper ends thereof and the valve is normally held in 
a "fail-safe" closed condition when the piston 61 is adjacent the upper 
end of the piston chamber as shown in FIG. 1. It is to be understood, of 
course, that the openings 26, 27 could be located nearer the lower end of 
the gate assembly such that the valve is in open condition when the 
actuator pistons are adjacent the upper end of the actuator housing. 
Application of pneumatic fluid to the actuator would then actuate the 
valve to its closed condition. 
To facilitate piston operation, a single opening 72 is provided through the 
lower end member 42 of the actuator 9 so that the interior of the actuator 
housing below the piston 61 is exposed to atmospheric pressure. Also, for 
safety reasons a pressure relief valve may be installed in an opening 74 
provided in the closed end of the actuator housing member 40A as shown in 
FIG. 1 and in phantom lines in FIG. 2. 
Affixed as by welding or otherwise, to the underside of the piston 75 and 
coaxially aligned therewith is a cylindrical down-stop member 85. The 
drive piston 61 is disposed in close fitting relation to the inner wall of 
the cylindrical downstop 85 and is adapted for sliding motion therein. A 
fluid-tight seal is established between piston 61 and the inner wall of 
the downstop 85 by means of a piston ring or seal 86 located in a 
circumferential groove formed about the piston 61. It will thus be seen 
that the cylindrical downstop 85 and the piston 75 which closes off one 
end thereof constitute a piston chamber 87 for accommodating axial and 
reciprocal motion of the drive piston 61. 
As seen in FIG. 1, wherein the actuator 9 is shown in its relaxed 
"fail-safe" valve closed position, the position 61 is "nested" against the 
underside of the piston 75. It will thus be seen that upon admission of 
pressurized pneumatic fluid into the piston chamber through the fluid 
inlet, the fluid acting on the fluid receiving face, the piston 75 will 
overcome the force of the springs 66, 67 and drive both pistons 75 and 61 
towards the end of the actuator housing mounted on the valve housing. 
Accordingly, the actuator stem 23 is driven downwardly as shown in the 
drawings, to move the gate assembly transversely with respect to the flow 
passages 13, 14 of the valve and place the gate assembly in the open 
position wherein the ports 26, 27 of the gate assembly elements are 
disposed in register with the flow passages 13, 14 and the gate assembly 
is in its expanded wedged sealing condition. During the actuator stroke, 
however, the stroke of the piston 75 is terminated before there is a 
termination of the stroke of the drive piston 61 due to the engagement of 
the lower end surface 85A with the surface 86 of the end member 42 of the 
actuator housing. The axial length of the downstop 85 is selected such 
that the stroke of the piston 75 is terminated at the instant where the 
gate assembly ports 26, 27 move into fluid communication with the flow 
passages 13, 14 of the gate valve 10. 
In order that the drive piston 61 may continue its stroke under the 
application of actuating pneumatic fluid into the piston chamber 41, a 
small orifice 91 is provided to extend through the piston 75. The orifice 
91 restricts and controls the flow of actuating fluid into the chamber 
void formed between the pistons 61 and 75 as the drive piston 61 continues 
its stroke. The resulting drop in fluid pressure driving the piston 61 
operates to impose a substantially constant velocity on the piston 61 
throughout the remainder of the actuator stroke and thereby prevent a 
damaging rapid acceleration and momentum build-up of the piston-stem-gate 
assembly drive "train". 
It is to be understood, of course, that the piston chambers 41 and 87 are 
fluid-tight with respect to the pistons 75 and 61 with the exception of 
the orifice 91. Accordingly, a seal 93 is provided to seal between the 
piston guide 77 and adapter 62 and seal 94 is provided to seal the 
connection between the adapter 62 and piston 61. In addition, an annular 
piston guide 92 is affixed to the inner wall of the actuator housing 
member 40B in close fitting relation about the stop member 85 and serves 
to guide the piston 61. The piston guide 77, which extends externally of 
the actuator housing, makes it possible to manually override the actuator 
9 to operate the gate valve 10. 
It is to also be understood that the foregoing description of a preferred 
embodiment of the invention has been presented for purposes of 
illustration and description and is not intended to limit the invention to 
the precise form disclosed. For example, the particular type of expanding 
gate valve may be other than shown. It is also possible to use a stop 
means other than the cylindrical member 85 for purposes of terminating the 
stroke of the primary piston. Diaphragm-type pistons could also be used in 
lieu of rigid pistons 75 and 61. It would also be feasible to adapt the 
dual stage actuator of this invention to operate various mechanisms other 
than gate valves where it is advantageous to reduce the latter stage of 
actuator thrust. Accordingly, is to be appreciated that changes may be 
made without departing from the spirit of the invention.