Abstract:
A gate valve actuator including an housing, a piston, a lower end closure, and a piston cylinder end cap. The piston is situated within the housing, and the lower end closure connects the housing and the piston. The piston cylinder end cap also connects the housing and the piston. The housing, the piston, the lower end closure, and the end cap define a main actuator cavity. The connection between the lower end closure and the piston and the connection between the piston cylinder end cap and the piston are sealable connections. The main actuator cavity is substantially isolated from ambient air and from a control fluid, which prevents moisture build-up and hence prevents corrosion of the internal components of the actuator.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/828,184 filed on Oct. 4, 2006. 
     
     BACKGROUND 
       [0002]    Hydrocarbons, such as oil and gas are produced at a wellhead and conveyed through flow lines to remote gathering stations. Safety valves are conventionally used to automatically shut off flow upon the occurrence of some triggering event, such as unacceptable fluctuations in liquid level or pressure or temperature, or an electrical power loss. Additionally, safety valves may shut off flow when a catastrophic failure occurs due to explosion, storm damage, and the like. 
         [0003]    Examples of typical safety valves include gate valves with hydraulic actuators, such as those disclosed in U.S. Pat. Nos. 4,744,386 and 4,836,243, which are hereby incorporated by reference. 
         [0004]    Conventional valves with hydraulic actuators have a housing cavity, with a housing cavity volume that changes as the actuator strokes. To allow for this change in volume, without undesirable pressure change, the housing cavity is generally vented to the surrounding environment. Therefore, as the actuator strokes, ambient air moves into and out of the actuator housing. This movement of ambient air into and out of the actuator can introduce moisture, salt spray, or other contaminants into the actuator housing. This can cause a number of problems. For example, moist air within the actuator housing may condense out on the inside of the actuator, for example, when the actuator cools at night. As the actuator strokes, more and more condensate may accumulate inside of the actuator. Condensate may corrode the actuator&#39;s components. In some cases, the corrosion inside the actuator may be severe. Additionally, condensate may cause the visual position sight glass to become “fogged” over, such that the position indicator cannot be seen at all. In cold environments, condensate may freeze, preventing the actuator from working properly. 
       SUMMARY 
       [0005]    The present invention relates generally to valve actuators. More specifically, the present invention relates to gate valve actuators for use with hydraulic gate valves. 
         [0006]    In one embodiment of the present invention, the gate valve actuator includes a housing, a piston, a lower end closure, and a piston cylinder end cap. The piston is situated within the housing, and the lower end closure connects the housing and the piston. The piston cylinder end cap also connects the outer housing and the piston. The connections between the lower end closure and the piston and between the piston cylinder end cap and the piston are sealable connections. The housing, the piston, the lower end closure, and the piston cylinder end cap define a main actuator cavity. The main actuator cavity is substantially isolated from ambient air and a control fluid that applies pressure to the piston, and the main actuator cavity will remain at a substantially constant volume. 
         [0007]    In another embodiment of the present invention, the gate valve actuator includes a housing, a piston, a lower end closure, and a piston cylinder end cap. The piston is situated within the housing, and the lower end closure connects the housing and the piston. The piston cylinder end cap also connects the outer housing and the piston. The connections between the lower end closure and the piston and between the piston cylinder end cap and the piston are sealable connections. The housing, the piston, the lower end closure, and the end cap define a main actuator cavity. The main actuator cavity is substantially isolated from ambient air and a control fluid. The piston is capable of stroking along an axis parallel to the axis defined by the piston&#39;s connections to the lower end closure and the piston cylinder end cap. The volume of the main actuator cavity will remain substantially constant as the piston strokes. 
         [0008]    In one embodiment of the present invention, the gate valve actuator includes a housing, a piston, a lower end closure, and a piston cylinder end cap. The gate valve actuator also includes a stem, a downstop, and a bonnet. The piston is situated within the housing, and the lower end closure connects the housing and the piston. The piston cylinder end cap also connects the outer housing and the piston. The connections between the lower end closure and the piston and between the piston cylinder end cap and the piston are sealable connections. The stem is situated within the housing below the lower end closure and extends along the same axis as the piston. The stem is connected to the lower terminus of the piston, and has a different diameter than the piston. The downstop connects the stem and a portion of the housing which is below the housing&#39;s connection to the lower end closure. The bonnet connects the housing to a valve body. The housing, the piston, the lower end closure, and the end cap define a main actuator cavity. The lower end closure, the stem, the downstop, the housing, and the bonnet define an inner cavity. The piston and the stem are capable of stroking along an axis parallel to the axis defined by the piston&#39;s connections to the lower end closure and the piston cylinder end cap. The main actuator cavity is substantially isolated from ambient air and a control fluid, and the main actuator cavity will remain at a substantially constant volume as the piston strokes. The volume of the inner cavity will change as the piston strokes relative to the inner cavity. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The following figures form part of the present specification and are included to demonstrate certain aspects of the present invention. The present invention may be better understood by reference to one or more of these drawings in combination with the description of embodiments presented herein. 
           [0010]    Consequently, a more complete understanding of the present disclosure and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which the leftmost significant digit(s) in the reference numerals denote(s) the first figure in which the respective reference numerals appear. 
           [0011]      FIG. 1  is a partially cutaway side view of one embodiment of an actuator in accordance with the present invention. 
           [0012]      FIG. 2  is a partially cutaway side view showing another embodiment according to the present invention. 
           [0013]      FIG. 3  is a partially cutaway side view showing yet another embodiment according to the present invention. 
           [0014]      FIG. 4  is a partially cutaway side view showing still another embodiment according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Referring now to  FIG. 1 , shown therein is a fail-safe gate valve actuator  100 , attached to a gate valve  105  in accordance with one embodiment of the present invention. The actuator  100  of  FIG. 1  causes the valve  105  to close upon the occurrence of any triggering event, such as, but not limited to, power failure, pressure rise, pressure drop, temperature rise, or temperature drop. Alternatively, in some circumstances it may be desirable that the actuator  100  cause the valve  105  to open upon the occurrence of any triggering event. 
         [0016]    When the valve  105  is in an open position (not shown), a gate opening  110  aligns with a seat  111  in a valve body  112 . The seat  111  is in fluid communication with a flow line  115 , such that when the valve  105  is open, fluid passes therethrough. In a closed position, the gate opening  110  is positioned away from the flow line  115 , and a gate  120  blocks the flow line  115 . The gate  120  is connected to a piston  125  via a stem  130 . The piston  125  may be moved to or held in the open position (in the embodiment shown in  FIG. 1 , the “down” position), with control pressure, such as hydraulic, pneumatic, or other pressure from a control fluid, applied to the piston cavity  163 . The piston  125  may be moved to or held in the closed position (in the embodiment shown in  FIG. 1 , the “up” position), with a spring  135  acting upon a thrust ring  140  affixed to the piston  125 . The thrust ring  140  may be affixed to the piston at a location on the piston that is disposed between the piston&#39;s connection to the piston cylinder end cap  160  and the piston&#39;s connection to the lower end closure  155 . The thrust ring  140  may be moveable and loaded by the spring  135 . The spring  135  will shift the piston  125  to the “up” position when hydraulic fluid is released from the actuator  100 . The bottom of the spring  135  rests on a stationary lower end closure  155 . 
         [0017]    The lower end closure  155  may be of unitary construction, having a lower lip  155   a , an elongated portion  155   b , and an upper lip  155   c . The upper lip  155   c  may extend substantially radially outward from the piston  125  to the elongated portion  155   b . The elongated portion  155   b  may extend from the upper lip  155   c , substantially parallel to the piston  125 , to the lower lip  155   a . The lower lip  155   a  may extend substantially radially outward from the elongated portion  155   b  to a housing  150  of the actuator  100 . While unitary construction is disclosed and shown, the lower end closure  155  may be constructed in any of a number of ways. 
         [0018]    The thrust ring  140  and the spring  135  may be positioned within a main actuator cavity  145 . The main actuator cavity  145  may be defined by the piston  125 , the housing  150  of the actuator  100 , the lower end closure  155 , and a piston cylinder end cap  160 . The piston  125  may lie within the housing  150 . The piston cylinder end cap  160  may connect the piston  125  and the housing  150  at a first latitude of the housing  150 . The lower end closure  155  may connect the piston  125  and the housing  150  at a second, lower latitude of the housing  150 . The connections between the piston  125  and the piston cylinder end cap  160  and between the piston  125  and the lower end closure  155  may be slidable sealable connections so that a seal is maintained as the piston  125  strokes and slides along the relatively stationary piston cylinder end cap  160  and the lower end closure  155 . While the piston  125  may move relative to the main actuator cavity  145 , the volume of the main actuator cavity  145  will remain substantially constant. This volume remains substantially constant because the piston  125  has a substantially uniform diameter, at least through the portion defining the main actuator cavity  145 . Thus, as the piston  125  strokes, the volume of the piston  125  entering the main actuator cavity  145  is the same as the volume of the piston  125  exiting the main actuator cavity  145 . 
         [0019]    Seals  165  may isolate the main actuator cavity  145 , preventing the introduction of a control fluid or air having moisture or other potential contaminants into the main actuator cavity  145 . The seals  165  may be any type of seal known to one having ordinary skill in the art. For example, but not by way of limitation, the seals  165  may be made of a resilient material, such as an elastomer or a thermoplastic. The seal may also be made of a non-resilient material that is mechanically energized, such as a spring energized thermoplastic seal. Seals  165  also desirably maintain a liquid tight seal with the piston cavity  163  and the main actuator cavity  145 . The seals  165  desirably maintain a substantially airtight seal between the main actuator cavity  145  and the ambient air, preventing weepage into or out of the actuator cavity  145 . The seals  165  may form a hermetic seal. The seals  165  may be placed at a number of different locations at or near the boundary of the main actuator cavity  145 . For example, seals  165  may be placed between the lower end closure  155  and the piston  125 , between the piston  125  and the end cap  160 , between the end cap  160  and the housing  150 , and between the housing  150  and the lower end closure  155 . While seals  165  are shown at these locations, seals  165  are not required at all of these locations. For example, the lower end closure  155  could be fixedly attached to the housing  150 , and other boundary connections may be made in a similar fashion. The seals  165  may be factory installed. 
         [0020]    As the piston  125  moves up or down, the seals  165  between the piston  125  and the end cap  160  and between the piston  125  and the lower end closure  155  minimize the passage of control fluid and/or air into or out of the main actuator cavity  145 . This keeps the spring  135 , the thrust ring  140 , and other components in the main actuator cavity  145  free from excessive exposure to moisture, salt spray, and other contaminants, which can hinder the operation of the components. The air within the main actuator cavity  145  may also be purged with a gas, such as nitrogen, in order to further eliminate moisture from the inside of the actuator  100 . 
         [0021]    The housing  150  may include a sight glass housing  170  with a sight glass  175 . The sight glass  175  allows the position of the piston  125  to be observed externally, and thereby provides a means to determine the position of the gate  120 . An indicator  180  may attach to the thrust ring  140 , such that the indicator  180  indicates the position of the thrust ring  140 , and thus, the piston  125 . When the main actuator cavity  145  is substantially isolated from contaminants, the surface of the sight glass  175  that faces the main actuator cavity  145  will remain clear, allowing for accurate readings of the piston position as indicated by indicator  180 . 
         [0022]    In addition to the main actuator cavity  145 , the actuator  100  is formed with an inner cavity  185 . The inner cavity  185  may be smaller than the main actuator cavity  145 . The interior wall of the inner cavity  185  is defined by the piston  125  and the stem  130 . The exterior wall of the inner cavity  185  is defined by a bonnet  190  connecting the housing  150  to the valve body  112  and a portion of the housing  150  just above the bonnet  190 . An intermediate wall of the inner cavity  185  is defined by the lower end closure  155  and a downstop  196 . The upper lip  155   c  of the lower end closure  155  and a lower lip of the downstop  196  define the upper and lower bounds of the inner cavity  185 . When the piston  125  moves relative to the inner cavity  185 , the volume of the inner cavity  185  changes. This volume changes because the piston  125  and the stem  130  have different diameters. 
         [0023]    The inner cavity  185  may have a vent  195 . The vent  195  allows air to enter or exit the inner cavity  185  as the piston  125  moves. The vent  195  is located in the housing  150 . Since the components located in the inner cavity  185  would not be significantly affected by moisture or other contaminants, the introduction of ambient air into the inner cavity  185  would not significantly impair the performance of the actuator  100 . While the vent  195  is desirable, it is not necessary. Instead of being vented, the air within the inner cavity  185  may experience a pressure change. 
         [0024]    The downstop  196  stops the piston  125  from moving the stem  130 , and thus the gate opening  110  beyond the seat  111 . Thus, the downstop  196  may cause proper alignment of the gate  120  for flow of fluid through the flow line  115  when the valve  105  is in the open position. 
         [0025]    Referring now to  FIG. 2 , shown therein is another embodiment of the actuator  100  of  FIG. 1 . In addition to the features disclosed above with respect to  FIG. 1 , the actuator  100  of  FIG. 2  includes an electronic position indicator  200 , which is well known in the art. 
         [0026]    Referring now to  FIG. 3 , shown therein is another embodiment of the actuator  100  of  FIGS. 1 and 2 . The actuator  100  of  FIG. 3  is similar to the actuator  100  of  FIG. 2 , with a major difference being the size of the various features. For example, but not by way of limitation, the flow line  115  of  FIG. 3  may be smaller than the flow line  115  of  FIG. 2 . While size is not intended to be a limitation on any of the features,  FIG. 3  illustrates how the various features may be modified to accommodate different conditions. 
         [0027]    Referring now to  FIG. 4 , shown therein is yet another embodiment of the actuator  100  of  FIGS. 1-3 . The actuator  100  of  FIG. 4  is similar to the actuator  100  of  FIGS. 1-3 , with a major difference being the addition of a rod  400  extending out of the end of the piston  125 . The rod  400  may provide a visual position indication and allow a lock open cap (not shown) to be attached to the actuator  100  when the rod protector housing  410  is removed. 
         [0028]    The actuator  100  of the present invention is desirably a hydraulic valve. However, it may also be operated manually, or pneumatically as conditions dictate. The actuator  100  may be applied to applications either onshore or offshore. Additionally, while a “fail-safe close” type valve is shown and described, the features of the present invention may also be used with minimal modification to a “fail-safe open” type valve. 
         [0029]    Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee.