Fluid handling – Processes – Cleaning – repairing – or assembling
Reexamination Certificate
2002-03-11
2004-02-24
Rivell, John (Department: 3753)
Fluid handling
Processes
Cleaning, repairing, or assembling
C137S315330, C137S512000, C137S527200, C137S527400
Reexamination Certificate
active
06694996
ABSTRACT:
TECHNICAL FIELD AND BACKGROUND OF THE INVENTION
This invention relates to a type of valve known as a “check-valve.” Check valves are well known and are widely used to control backflow of fluids carrying undesirable contaminants into a fluid supply. These valves have evolved to become highly specialized in their function and operation, and are similar in that they all contain spring-loaded members that are biased toward the valve-closed position until fluid pressure acting on the checking members forces the valves open. Typically, a backflow preventer utilizes two check valves in a conventional serial combination for preventing the backflow of a fluid.
The pressure required to open a check valve is established by governmental regulation and provides a minimum degree of protection against reverse flow. Furthermore, regulations governing backflow preventers require that a check valve and associated parts must be removable for inspection and field service repair without having to remove the valve housing from the fluid conduit system to which it is attached.
In a conventional check valve design, the checking member is a poppet-type check in which the movement of the checking member is linear and remains in the fluid path. The energy required to open these check valves is provided by the fluid and is created at the source by, for example, a pump. The total energy of the fluid in motion is reduced by friction within the pipes and other obstacles in the fluid conduit system. Such obstacles include the checking members, which remain disposed directly in the fluid path once the check valves are open. This energy loss, also known as “headloss,” should be as low as practicable in order to preserve fluid pressure.
Many designs have been proposed to reduce the headloss created by poppet check valves. One design uses a “swing check” type design in which the checking member, also called a clapper, rotates about a fixed hinge pin. The swing check valve is advantageous because it allows the checking member to move out of the path of fluid flow, thereby reducing the headloss associated with conventional poppet-check valves. Clapper and spring assemblies in these conventional swing check designs can be oriented so that as the clapper moves away from the valve-closed position, the torque produced by the spring force about the pivot axis of the clapper through the hinge pin is reduced, thereby further minimizing headloss.
Conventional swing check valves used in backflow preventers generally incorporate the same components. Typically, the clapper in such valves creates a fluid seal across a valve seat. The valve seat surrounds an opening through which fluid would otherwise flow. The valve seat is also usually positioned adjacent to a fluid inlet port in a valve housing of the fluid conduit system and is typically mounted by bolts to the valve housing. As the fluid flows through the port in the downstream direction, the clapper opens by rotating about a hinge pin that is positioned adjacent and parallel to the valve seat face. A helical compression spring is typically used to exert force onto the backside of the clapper. The quantity of water allowed to flow through the swing check valve directly depends on the opening angle of the clapper and the force of the compression spring on the clapper, which in turn acts to oppose the opening of the clapper. The force of the spring on the clapper is a function of the degree of compression between the clapper and some other rigid structure such as the valve housing—fluid pressure must exceed a predetermined magnitude to overcome the spring force on the clapper in order to open the valve.
A toggle-linkage swing check valve is disclosed in Ackroyd, U.S. Pat. No. 5,236,009 (“the '009 patent”). The swing check valve of the '009 patent includes a valve assembly having a clapper, spring, and valve seat connected together as a unit. The valve is pivotally mounted at opposite ends to the valve seat and clapper for reorientation of the spring force during movement of the clapper so that the resultant torque applied to the clapper decreases as the clapper moves away from the valve-closed position. A disadvantage to the swing check backflow preventer of the '009 patent is that when the valve requires maintenance, a cover of the valve housing must be removed and then retaining wires must be removed so that the valve assembly can be manually disengaged from the inlet and then withdrawn from the valve housing. Installation of the valve includes the reverse steps.
Another toggle-linkage swing check valve is disclosed in Dunmire, U.S. Pat. No. 4,989,635 (“the '635 patent”). The check valve of the '635 patent includes a valve assembly having a spring, clapper, and valve seat connected together as a unit. The spring is positioned between the clapper and a wall of the valve housing. The wall is preferably a recess defined in the cover of the valve housing. Moreover, the spring is positioned within the recess and pivotally mounted to the clapper for urging the clapper into the valve-closed position so that the torque produced by the spring on the clapper decreases as the clapper pivots away from the valve-closed position. The clapper is attached to the valve seat, which is in turn mounted by bolts to the valve housing. A disadvantage to the swing check valve of the '635 patent is that replacing the valve assembly requires that the housing cover first be removed. The bolts that attach the valve assembly to the valve housing must then be removed. Only then may the valve assembly be withdrawn from the valve housing, provided that careful control of the spring is maintained. Without such control, the spring becomes free to pivot about its attachment to the clapper once the cover is removed. The valve assembly of the '635 patent thus presents an awkward handling situation whenever the valve assembly requires assembly, replacement, or maintenance.
Yet another design for swing check valves is the “Regev” valve manufactured by A. R. I. Kfar Charuv of Ramot Hagolan, Israel. The valve includes a valve housing having a spring and a clapper that are positioned adjacent an inlet port of a valve housing. The spring includes a spring base, and the clapper has a cam member that remains in continuous engagement with the spring base. The clapper is mounted to the valve housing by a hinge pin. The spring is positioned in a valve housing recess above the clapper and is axially compressible in a direction perpendicular to fluid flow through the valve housing. This forces engagement of the spring base with the cam member to force the clapper toward the valve-closed position. The spring does not vary in its orientation during movement of the clapper as in the toggle-linkage designs discussed above, i.e., the spring is not pivotally mounted at its ends. The torque produced by the spring force on the clapper about the hinge pin is reduced as the clapper moves away from the valve-closed position, thereby minimizing headloss. A disadvantage to the Regev valve is that, in order to replace any component of the valve assembly or replace the entire valve assembly itself, the entire valve housing must be removed from the fluid conduit system and replaced. Furthermore, unlike the valves of the '009 and '635 patents, there is no valve assembly disposable within a valve housing in the Regev valve which can be removed from a fluid conduit system without removing the valve housing as required by backflow preventer regulation.
More recent designs for swing-type backflow preventer valves are disclosed in applicant's U.S. Pat. Nos. 5,711,341 and 5,794,655. Both of these patents disclose a valve housing having a spring and a clapper that are positioned adjacent an inlet port. The spring includes a base, with the rocker arm of the clapper having a roller which remains in continuous engagement with the spring base. The top end of the spring is attached to the interior surface of a hydraulic tap threaded into the valve housing. The clapper is mounted to the valve housing
Adams Evans P.A.
Conbraco Industries, Inc.
Rivell John
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