Valves and valve actuation – Reciprocating valve
Reexamination Certificate
2002-08-19
2004-01-20
Mancene, Gene (Department: 3754)
Valves and valve actuation
Reciprocating valve
C251S367000, C277S316000, C277S437000
Reexamination Certificate
active
06679477
ABSTRACT:
SPECIFICATION
1. Field of the Invention
The present invention relates generally to valves suitable for abrasive fluids, such as drilling mud, under high pressures. More specifically, the invention relates to valve bodies for use in web-seat, stem-guided valves wherein the valve body comprises at least one integral seal retention groove.
2. Background of the Invention
A valve suitable for abrasive fluids such as oil field drilling mud comprises a valve body and a corresponding valve seat, with certain valve bodies incorporating an elastomeric seal within a peripheral seal retention groove. Such a valve is usually mounted in the fluid end of a pump incorporating positive displacement pistons or plungers in multiple cylinders. Such valves are frequently web-seat, stem-guided designs adapted for high pressures and repetitive high-impact loading of the valve body and valve seat. Thus, they are expensive to manufacture, especially the moving portion or valve body. Besides requiring finish machining to close tolerances for adequate sealing, such valve bodies must be made strong enough to resist significant distortion under load with resultant leaks and fatigue failures. Prior efforts to reduce distortion under load by strengthening such valve bodies have generally resulted in higher cost and/or heavier designs which exacerbate sealing problems and/or increase the stress of impact loading on components of the valve assembly.
Commercially important design improvements necessarily reflect the fact that certain mud pump valve body and seat dimensions are effectively limited by industry practices and American Petroleum Institute (API) Standards. For example, the web-seat, stem-guided designs favored for mud pump valves are commonly made compatible with the industry benchmark widely known as the TRW Mission 4-web seat, which determines many valve dimensions. Further, API Standards determine the envelope into which valve bodies and seats must fit to promote interchangeability in the field.
Given these constraints, attempts to reduce fatigue failures and/or improve valve performance have led to “improved” designs which are more expensive to manufacture and have different failure modes than earlier versions. For example, valve bodies with circular “Channel-Beam” sections may incorporate a forged bowl shape as seen, for example, in
FIG. 1
of U.S. Pat. No. 5,249,600, the entire patent being incorporated herein by reference. This forged valve body has exceptional stiffness and strength.
But such valve bodies have several disadvantages in manufacture and use. First, rough valve body forgings in the Channel-Beam shape require substantial material removal in finish machining of the integral seal retention groove. Second, an elastomeric seal snapped into the seal retention groove may not fully seat around the entire valve body, causing an out-of-round condition that can result in early valve failure. Third, certain portions of the valve body may be made relatively thin to reduce weight, but such thin portions require particular care during heat treatment to avoid excessive brittleness. Avoidance of thin portions, on the other hand, imposes weight penalties that result in greater impact loading. Similar disadvantages are generally present in other Channel-Beam designs, such as those described in U.S. Pat. Nos. 3,191,617; 3,202,178; 3,742,976; 4,180,097; 5,345,965; and 5,431,186, all incorporated herein by reference.
Notwithstanding their relatively high cost, however, valve bodies having an integral seal retention groove (i.e., a seal retention groove having no removable seal retention plate or other analogous removable structural member) such as the one-piece Channel-Beam design have gained limited industry acceptance. Their high strength and stiffness effectively counter valve body distortion about one or more radial axes (i.e., axes radiating perpendicularly from the valve body's longitudinal axis of symmetry). This type of distortion is particularly a problem on valve bodies that mate with web seats. Cyclical high pressure applied to such a valve body when it is sealed against a web seat tends to repeatedly force portions of the valve body into the spaces between the seat webs. The periphery of the disc-shaped area of the valve body (commonly called the flange) tends to wrinkle like a cupcake paper, the number of wrinkles being equal to the number of seat webs.
On multi-piece valve bodies (i.e., valve bodies having a removable seal retention plate), such cyclic loading induces fatigue that can lead to further distortion and/or failure of the valve flange. Countering such distortion by simply making the flange thicker increases total valve body weight, which in turn increases wear due to higher impact loading of both the valve body and seat. Valve bodies of Channel-Beam design minimize such distortion in part through their inherent rigidity and strength, but they weigh even more than comparable multi-piece valve bodies and so suffer the disadvantage of higher impact loads in use.
Another important disadvantage of the Channel-Beam design, as noted above, relates to seating of the seal insert. Channel-Beam valve bodies generally incorporate an elastomeric seal insert that snaps into its peripheral seal retention groove. A typical “snap-on” seal insert comprises a portion of a toroidal structure such as a plastic or rubber ring that is sized to fit tightly, and thus sealingly, in the peripheral seal retention groove. When properly fitted, the elastomeric seal mates tightly with a corresponding valve seat even though the valve body is slightly distorted and even if small particles carried by the pumped fluid may be trapped between sealing surfaces. Practical advantages of such a seal insert include extended valve life and improved valve performance, but proper fitting and sealing of the elastomeric ring on a valve body is often difficult in the field.
For example, the snap-on insert may not exactly fit the Channel in a Channel-Beam valve body. The installed seal may then be out-of-round, leading to premature seal failure and subsequent failure of the valve body and web seat. When such a seal fails, leaking high-pressure fluid will jet through the initial leak path. If the valve remains in service, the leaking, jetting high-pressure fluid will literally wash away the hardened steel of the valve body and/or seat. Multiple and near-simultaneous failures of a single seal ring may give a valve body flange the appearance of a wrinkled cupcake paper.
Leaks due to seal displacement within a seal retention groove may even occur when elastomeric seals are cast and cured in place unless a special adhesive is first applied to the groove. Such bonding of the cured seal to the groove wall is expensive, and it also tends to reduce the service life of the seal due to internal stress induced as the curing elastomer tends to shrink away from the walls to which it is bound. Additionally, field replacement of such seals is not practical.
Another disadvantage of Channel-Beam valve bodies is their relatively high manufacturing cost. They are expensive to manufacture because the forgings from which they are machined are not near-net-shape. Significant machining time is needed to remove excess material from the seal retention groove (the Channel). Further, because of their characteristic shape, Channel-Beam valve bodies require longer or special nonstandard springs to accommodate the extra depth of the bowl.
Problems associated with high machining and materials costs, as well as seal movement and/or out-of-round seal placement, are reduced in valve bodies which incorporate a separate (removable) seal retention plate which commonly screws or bolts to the valve body to form at least part of one wall of a seal retention groove. Separate seal retention plates can be forged to near-net-shape, and they reduce the time required to correctly replace toroidal sealing rings. But they also raise valve fabrication costs and impose use restrictions. For example, they add excess weight to the moving valve body, aggravating impact
Buechner Patrick
Gilstad Dennis W.
Mancene Gene
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