Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02204681 1997-0~-07
GATE VALVE BONNET ASSEMBLY WITH BUILT-IN SPEED REDUCER
BACKGROUND OF TIIE INVENTION
1. Field of the Invention
The present invention relates to a gate valve bonnet assembly. More
specifically, the present invention relates to a bonnet assembly having a built-in speed
reducer which slows down the valve opening cycle of a pneumatically act~lated gate valve
5 while allowing rapid return during the valve closure cycle.
2. Description of Related Art
Gate valve pneumatic actuators are pressurized to the control pressures
required to operate the gate valve. This stored energy in the actuator is b~l~nced against
10 the valve pressure and frictional forces. However, as soon as the gate is cracked open, the
oppositional forces disappear, thereby causing rapid movement and sl~.. ing ofthe
actuator and the internal components of the valve. This rapid movement is responsible for
serious damage to the gate and seat sealing surfaces which are under very high contact
stresses during the actuation or opening cycle. Sometimes the damage will render the valve
15 incapable of further pressure sealing. The cl~mming action can also cause serious structural
damage to the various linkages between the actuator and the valve bonnet.
The closing cycle of the valve gate is significantly di~-ent because the gate
and seats are not under high contact stresses during the closing cycle. Therefore, rapid
movement does not damage the sealing surfaces. In fact, during the closing cycle, it is
20 desirable to have rapid movement of the valve to prevent excessive erosion of the gate and
seats as the valve pinches closed.
Several actuator m~nllfachlrers are attempting to develop external speed
red~lçing devices which can be mounted on top of pneumatic actuators. However, such
add-on units adversely affect the overall length of the act lated valve assembly, which has
25 become critical in limited space situations, such as in offshore applications.
The object of the present invention is to overcome the aforementioned
drawbacks of the prior art and to provide a gate valve with a bonnet assembly having a
built-in speed reducer.
CA 02204681 1997-0~-07
SUMMARY OF TEIE INVENTION
The objects of the present invention are achieved by providing a bonnet
assembly mounted on the body of a gate valve and including a bonnet housing having a
5 central bore therethrough and a chamber along the central bore; a valve stem movably
positioned within the central bore and including a first end coupled to the gate of the gate
valve and a second end coupled to a valve actuator for moving the valve stem and gate
between a closed position and an open position; a piston movably positioned within the
chamber and having at least one damping hole therethrough; a flange attached to the valve
10 stem against the piston for moving the piston from a first position to a second position when
the valve stem is moved between the closed position and the open position; and amerh~ni~m for independently moving the piston from the second position to the first
position when the vatve stem is moved between the open position and the closed position.
In one embodiment of the present invention, the piston is formed of an
15 annular piston slidably received on the valve stem, the chamber within the bonnet housing is
filled with hydraulic fluid and the device for independently moving the piston to the first
position is a spring positioned with the chamber biasing the piston toward the flange. The
valve stem and the piston may be cylindrical with a first seal between the piston and the
bonnet housing and a second seal between the piston and the valve stem. Additionally, the
20 flange can include a beveled edge with the piston further inclu-ling a beveled portion for
receiving the beveled edge to ensure a secure engagement between the components.These and other objects of the present invention will be clarified in the
description of the prefelled embodiment taken together with the attached figures, wherein
like reference numerals lep-ese.ll like characters throughout.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a cross-sectional view of the gate valve according to the present
invention with the gate valve in the closed position;
Fig. 2 illustrates the bonnet assembly of the gate valve shown in Fig. I with
30 the valve stem of the bonnet assembly in the open position;
CA 02204681 1997-0~-07
Fig. 3 illustrates the bonnet assembly of Figs. 1 and 2 moving between the
closed position and the open position; and
Fig. 4 is an enlarged view of portion IV of the bonnet assembly shown in
Fig. 3.
s
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Fig. 1 illustrates a gate valve 10 according to the present invention. Gate
valve 10 incllldes a valve body 11 d~fining a fluid flow passage 12 therethrough between an
inlet 13 and an outlet 14. A gate chamber 16 extends though a portion of the body 11 at a
right angle to and intersecting the fluid flow passage 12. The passage 12 includes a pair of
enlarged portions adjacent the gate chamber 16 into which is fitted a pair of cylindrical
valve seats 22 and 23. Each valve seat may include an annular sealing member mounted to
provide a fluid tight seal between the valve seats 22 and 23 and the enlarged portion of the
passage 12. Each ofthe valve seats 22 and 23 extends into the gate chamber 16, where it is
in sliding contact with a flat valve gate 30 having a port 34 therethrough.
When the gate 30 is positioned in the closed position, as shown in Fig. 1, the
gate 30 blocks the flow of fluid between the inlet 13 and the outlet 14 ofthe passage 12.
When the gate 30 is moved into an open position, the gate port 34 interconnects the inlet 13
and outlet 14 of the passage 12 to allow fluid to flow between the inlet 13 and the outlet 14.
However, fluid could also flow in the opposite direction from the outlet 14 to the inlet 13.
According to the present invention, gate valve 10 also includes a bonnet
assembly 40. Bonnet assembly 40 comprises a bonnet housing 41 having a bonnet housing
cap41A. Bonnetho~eing4l isatt~.hedtothebody 11 of gatevalve 10byapluralityof
cap screws 42. The bonnet housing 41 includes a central bore 43 eYten~iin~ therethrough
with a piston chamber 45 positioned along the central bore 43. A valve stem 48 is movably
positioned within the central bore 43 with a first end of the valve stem 48 ~tt~hed to the
gate 30 and a second end of the valve stem 48 att~ched to a pneum~tic valve actu~tor 50
(shown schematically in Fig. 1). The valve actuator 50 will move the valve stem 48 and the
gate 30 between the closed position and the open position.
CA 02204681 1997-0~-07
Appropriate packing 52 is provided around the valve stem 48 below the
piston chamber 45 to seal offpiston chamber 45 from gate chamber 16. The packing 52 is
secured in place by a pac~ing nut 54, and a passage 56 extends to the bore 43 through the
bonnet housing 41 at a position below the packing 52 for purposes oftesting packing 52.
5 In addition, bonnet assembly 40 incl~ldes O-rings 58 for sealing against the cylindrical valve
stem 48 at a position above the piston chamber 45.
Bonnet assembly 40 also comprises an annular cylindrical piston 60 movably
positioned within the piston chamber 45 and slidably received on the valve stem 48. The
details of the piston 60 can most clearly be seen in the enlargement shown in Fig. 4. The
piston 60 includes a first seal 61 between the piston 60 and the bonnet housing cap 41A and
a second seal 62 between the piston 60 and the valve stem 48. The piston 60 additionally
includes preferably a plurality of damping holes 64 e~ctending therethrough, evenly spaced
around the piston 60. The upper surface of the piston 60 includes an outwardly beveled
portion 66 adjacent the hole receiving the valve stem 48. Additionally, the lower surface of
15 piston 60 includes an annular groove 68 formed therein for purposes of centering a spring
74, which is discussed below.
Bonnet assembly 40 further incl~ldes a piston let~ i,-g flange 70 securely
~tt~hçd to the valve stem 48. The flange 70 incl~ldes a beveled lower edge 72 which is
adapted to abut and engage with the beveled portion 66 of the piston 60 when the valve
20 stem 48 is moved downward from the valve closed position, shown in Fig. 1.
A spring 74 is positioned within the piston chamber 45 with one end portion
of the spring 74 received within the annular groove 68 of the piston 60. The spring 74
biases the piston 60 toward the flange 70. The bonnet housing cap 41A incl~ldes a port 76
e~ct~n~ to the piston chamber 45, allowing for filling the piston chamber 45 with
25 appropriate hydraulic fluid.
The present bonnet assembly 40 will slow down the opening speed of
pnellrn~tically actu~ted valves, preventing gate 30, seat 22 and seat 23 from damage which
otherwise results from rapid movement of gate 30 under the inflll~nce of the stored pressure
energy of the pneumatic actuator 50. Additionally, the present bonnet assembly 40 permits
30 the use of the bonnet assembly 40 with any brand of pne~lm~tic or diaphragm actuators.
CA 02204681 1997-0~-07
The gate valve 10 according to the present invention operates as-follows. As
the pneumatic actuator 50 starts to exert a valve opening force to the valve stem 48 to
move the valve stem 48 from the closed position shown in Fig. 1 to the open position
shown in Fig. 2, that force will be transferred to the flange 70 which will in turn transfer the
force to the piston 60 through an engagement between the beveled lower edge 72 and
beveled portion 66. The flange 70 iS preferably a split ring to allow assembly onto the valve
stem 48, and is retained in place by a retainer ring 75. The beveled lower edge 72 of flange
70 and beveled portion 66 of piston 60 ensure that flange 70 will not separate under load.
Since the portion of the piston chamber 45 below the piston 60 is full of hydraulic fluid, any
10 downward movement of the piston 60 will be possible only when the hydraulic fluid has
been displaced under the piston 60 into the space above the piston 60 through the damping
holes 64. This restrictive fluid flow through the damping holes 64 will slow down the speed
of the piston 60 and valve stem 48, thereby red~lcing the speed of the valve opening cycle.
Fig. 2 illustrates the bonnet assembly in the fully open position.
The speed reduction of the present invention only operates with the opening
cycle and does not affect the closing cycle of the gate valve 10. As shown in Fig. 3, when
the gate valve 10 is closing, the valve stem 48 will move independently of the piston 60, and
is thereby free to act in a fast-acting capacity. The spring 74 will return the piston 60 to the
position illustrated in Fig. 1 independently of the movement of valve stem 48.
The damping holes 64 provided in the piston 60 provide appropriate
restriction of the fluid paCc~ge. The number and size of the damping holes 64 will vary
according to the size of gate valve 10 and the degree of damping desired. Additionally, as
~iccllcsed above, due to the relative movement between the valve stem 48 and the piston 60,
the speed reduction is only effective for the valve opening cycle.
The relative positions of the flange 70 and spring 74 with respect to the
piston 60 may be reversed if the opening and closing conditions of the gate valve 10 are
reversed, such as if the port 34 of the gate 30 were in the lower half of the gate 30 whereby
the positions of valve stem 48 and gate 30 in Fig. 1 corresponded to a valve open condition.
This and other various modifications will be appar~,nl to those of ordinary
30 skill in the art without departing from the spirit and scope of the present invention.
CA 02204681 1997-05-07
Consequently, the scope of the present invention is intended to be defined by the attached
clalms.
