The present invention relates generally to fluid flow control and, in particular, to an improved flow control valve assembly.
Control valves of the type to which this invention pertains are used to control or throttle high pressure fluid flows such as applications that involve steam flow.
The present invention provides a new and improved control valve assembly for controlling or throttling the flow of fluid such as steam.
According to one preferred embodiment of the invention, a flow control valve is provided that includes a valve housing that defines a valving chamber. A port member mounted within the valving chamber receives a reciprocally movable piston/spool assembly. The relative position of the piston/spool assembly within the port member determines the flow rate of fluid through the valving chamber. An actuator is used to move the piston/spool assembly within the port member. The piston/spool assembly is engageable with a valve seat which, when engaged, blocks fluid flow through the valving chamber. An actuating member is operatively connected to the piston/spool assembly and can move the assembly in opening and closing directions within the port member.
According to the invention, the piston/spool assembly includes a piston body that defines a seal recess for receiving an annular seal. The seal sealingly engages an inside surface of the port member and inhibits fluid flow between the piston/spool assembly and the inside surface of the port member. The assembly also includes a bonnet that is received by the piston body and is engageable with the annular seal. The seal, the bonnet and the actuating member are arranged such that when the actuating member moves the piston/spool assembly into sealing contact with the valve seat, forces are exerted on the annular seal by the bonnet which cause increased sealing engagement between the inside surface of the port member and the annular seal.
In the exemplary embodiment, the bonnet applies compression forces to the seal which, in turn, causes the seal to expand in the radial direction, thus increasing its sealing engagement with the inside surface of the port member.
According to a further feature of this embodiment, the actuating member abutably engages the bonnet and is attached to the associated piston body with a connection that allows relative movement between the actuating member and the piston body. With this preferred embodiment, when the actuating member moves the piston/spool assembly into sealing contact with the valve seat, the bonnet, by virtue of the lost motion connection (between the actuating member and the piston body) moves relative to the piston body a slight amount, thus applying forces to the seal that is captured between the bonnet and the piston body. These forces cause at least a portion of the annular seal to expand in the radial direction, thus increasing the sealing contact between the annular seal and the inside surface of the port member.
With the disclosed embodiment, the annular seal engages the inside surface of the port member with increased engagement force only when the piston/spool assembly is moved to a position where it sealingly engages the associated valve seat. When the actuating member moves the piston/spool assembly away from the valve seat, the compression forces applied by the bonnet are released, thereby relaxing the seal and reducing the friction between the seal and the inside surface of the port member. As a result, reciprocal movement of the piston/spool assembly within the port member is not resisted by a substantial frictional force that would be present if the seal were permanently preloaded to exert the substantial sealing engagement that is present when the piston/spool assembly is moved to its valve seat engaging position.
According to a further feature of the invention, a gap is preferably maintained between the bonnet and the piston body. The gap, in cooperation with pressure balancing passages equalizes fluid pressures on the piston/spool assembly.
The preferred method of controlling the flow rate of high pressure fluid in a control valve, includes the steps of providing a valve housing that defines a valving chamber, providing a port member within the valving chamber that receives a reciprocally movable piston/spool assembly. In addition, the method provides a valve seat engageable by the piston/spool assembly for blocking flow through the valving chamber. Enhanced sealing between the piston/spool assembly and an inside surface of the port member is provided by moving the overall assembly within the port member with an actuating member. The actuating member is allowed to move relative to a portion of the piston/spool assembly in order to allow another portion of the piston/spool assembly to move relative to the first portion thereby applying forces to the seal. This causes the seal to expand radially and to increase its sealing engagement with the inside surface of the port member.
With the disclosed invention, sealing between a piston/spool assembly and its associated port member are substantially increased when the piston/spool assembly engages its associated valve seat. When the piston/spool assembly is in a position other than its valve seat engaging position, the seal is relaxed. With the seal relaxed, friction between the seal and port member is reduced. Consequently, the relative movement between the piston/spool assembly and the port member is not substantially resisted by the engagement of the seal with the port member. Thus, the control of the fluid flow rate through the valving chamber is substantially improved.
Additional features of the invention will become apparent and a fuller understanding obtained by reading the following detailed description made in connection with the accompanying drawings.
The valve assembly 10 includes a valve housing 12, which includes a flow passage 20 having an inlet end 20a and an outlet end 20b. In the illustrated construction, the inlet and outlet ends 20, 20b define respective bolt flanges 22a, 22b to which suitable piping (not shown) is fastened in a known way.
The flow of fluid (i.e., steam) from the inlet 20a to the outlet 20b is controlled by a valving assembly indicated generally by the reference character 30. The valving assembly 30 includes a ported sleeve 32 that is fixed within a valve chamber 20c also defined by the valve housing 12. In the illustrated construction, the sleeve 32 may be captured within the valve body between a step 40 and a cylindrical spacer 42. A valve cap 50 exerts a clamping force on the sleeve 32. The valve cap 50 is secured by a plurality of studs 54 that extend upwardly from the valve housing 12, extend through bores 56 in the cap 50 and receive suitable nuts 58 which retain the cap in position and apply a clamping force to the cylindrical spacer 42.
A flow control piston or spool 60 is reciprocally movable within the sleeve 32 and when it is moved upwardly, (as viewed in
The valve assembly 10′ includes a valve housing 12′ that defines a flow passage 20′ having an inlet end 20a′, an outlet end 20b′ and a valve chamber 20c′. A valving assembly 30′ constructed in accordance with a preferred embodiment of the invention in located in the valve chamber 20c′ and controls the flow of fluid i.e. steam, from the inlet 20a′ to the outlet 20b′. The valving assembly 30′ includes a ported sleeve 32′ that is clamped between the seat or step 40′ and the annular spacer 42′.
The valving assembly 30′ includes a piston/spool assembly 60′ constructed according to a preferred embodiment of the invention. The piston/spool assembly 60′ is reciprocally movable within the port sleeve 32′ and controls or throttles fluid flow between the inlet 20a′ and outlet 20b′. It should be apparent that the more ports 32a′ that are exposed as the piston/spool assembly 60′ is raised (as viewed in
The piston assembly 60′ includes a piston body 76 having an upper, reduced diameter section 76a which defines an open-ended groove for receiving an annular seal 78. A compression bonnet 80 is at least partially received by the reduced diameter section 76a of the piston body 76 and includes a downwardly depending (as viewed in
Referring to
When the piston body 76 is in contact with seat 40′ and the stem 66′ continues to be urged downwardly by its associated actuator, the step 72 applies a downward directed force to the top of the compression bonnet 80 and urges it downwardly. This downward force causes the axial rim 80a of the bonnet 80 to exert a compression force on the annular seal 78 and may reduce its axial dimension (depending on the material composition of the seal 78). The compression of the seal 78 in the axial direction causes the seal to expand radially and thus create a tight sealing engagement between the upper part 80a of the piston body 76 and the inside surface of the sleeve 32′, thus inhibiting leakage between the piston body 76 and the sleeve 32.
In the preferred embodiment, the piston body 76 includes pressure-balancing bores 88 and the compression bonnet 80 includes arcuate slots 80b for equalizing fluid pressure above and below the piston assembly 60′ when the piston body 76 is in sealing contact with the associated seat 40′. In this position, fluid flow from the inlet 20a′ to the outlet 20b′ is blocked. Absent the balancing bores 88 and openings 80b in the bonnet 80, full inlet pressure would urge the piston body 76 upwardly, which would tend to move the piston assembly 60′ toward an open position. The communication of inlet fluid pressure to the top surface of the bonnet/80 (as viewed in
With the disclosed construction, sealing engagement of the piston body 76 to the sleeve 32′ is substantially enhanced without detrimentally affecting the ability of the piston assembly 60′ to be reciprocally moved within the sleeve 32′ by the associated actuator. Downward movement of the stem 66′ (by an associated actuator) causes compression of the annular seal 78 once the bottom edge or skirt 61 of the piston body sealingly contacts the associated seat 40′. As discussed above, compression of the annular seal 78 causes radial expansion, thus causing a tight engagement between the seal 78 and the inside surface of the ported sleeve 32′. However, when the piston body 76 moves off the seat 40′, as the stem 66′ is raised upwardly, the upward movement of the bonnet 80′ (which depending on the material from which the seal 78 is made may be very slight) relaxes the seal 78, thus decreasing the force necessary to reciprocally slide the piston assembly 60′ within the sleeve 32′ to achieve a desired flow rate. With the disclosed invention, when the piston body 76 is off its seat 40′, the piston assembly 60′ can be moved by the actuator relatively easily in order to control the flow rate through the valve. In normal operation, the actuator may continually move or dither the piston assembly 60′ within the sleeve in order to achieve a desired flow rate. In the prior art, the piston seal was fully loaded at all times, thus requiring significant actuator force to reciprocally move the piston within the sleeve even when the piston disengaged the associated seat.
It should be noted here, that the connection of the stem 66′ with the compression bonnet 80′ and piston body 76′ resembles a lost motion connection. In particular, the narrow diameter portion 66a′ of the stem 66′ can move relative to the piston body 76 a predetermined amount in order to relax and compress the seal 78. The distal end 66b of the stem 66′ is threaded and receives a nut 90 by which an initial pre-load is preferably applied to the seal 78 by the compression bonnet 80, to initially compress the seal 78 a minimal amount. When the stem moves downwardly from its relaxed position to its full force applying position shown in
As seen best in
In the preferred embodiment, a gap G was maintained between the underside of the compression bonnet 80 and the top of the piston body 76. Depending on the material composition of the seal 78, the gap may change slightly or substantially. In any event, in the preferred embodiment, a gap G preferably always exists even when the piston body 76 is in tight sealing engagement with the seat 40a. By maintaining a gap G throughout valve operation, the full downward force applied by the stem 66′ is always applied to the seal, rather than directly to the piston body 76. With this preferred construction, fluid communication between the pressure balancing bores 88 and the arcuate slots 80a is maintained even if the slots are not aligned with the bores 80a. In addition, any wear that occurs in the seal 78 is taken up by slight reductions in the gap G without reducing the forces applied to the seal when the piston body 76 is seated against the seat 40′.
Although the invention has been described with a certain degree of particularity, it should be understood that those skilled in the art can make various changes to it without departing from the spirit or scope of the invention as hereinafter claimed.
This application claims priority to U.S. Provisional Application No. 61/443,794, filed Feb. 17, 2011, the entirety of which is incorporated herein by reference.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US2012/025575 | 2/17/2012 | WO | 00 | 8/14/2013 |
Number | Date | Country | |
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61443794 | Feb 2011 | US |