1. Field of the Invention
The present invention pertains to valve apparatus. More specifically, the present invention pertains to valve apparatus for allowing fluid flow in one direction but preventing reverse fluid flow therethrough. In particular, the present invention pertains to valves particularly suitable for use with reciprocating pumps of the type used in subsurface oil well pumping.
2. Description of the Prior Art
Lift pumps for lifting subsurface fluids to the surface of an oil well have been in existence for many years. Lift pumps usually include a tubular barrel (which may be a portion of the production tubing) and a cooperating plunger assembly which reciprocataes therein. The plunger assembly may be attached to a rod which extends to the surface of the well and by which the plunger assembly may be reciprocated.
A lift pump typically includes a standing valve which is fixed relative to the pump barrel and a traveling value which is fixed to the plunger assembly. The standing valve and traveling valve, act as check values, opening and closing, opposite of each other, on upstrokes and downstrokes of the plunger assembly. For example, as the plunger assembly and the attached traveling valve are lowered on a downstroke, the standing valve is closed, blocking reverse fluid flow therethrough, and the traveling valve is opened allowing fluid within the pump barrel to be displaced through the traveling valve into the tubing thereabove. On the subsequent upstroke, the traveling valve closes, lifting the fluids thereabove toward the surface. Since pressure in the pump barrel below the traveling valve decreases during the upstroke, the standing valve then opens allowing fluid to flow into the pump barrel for a succeeding downstroke. As this process continues, fluid flows through the standing valve and into the pump barrel during the upstrokes and through the traveling valve toward the surface of the well on the upstroke.
Most of the standing valves and traveling valves of the prior art, provide a ball closure member which is carried for limited axial movement, within a ball valve cage, from a seated position, blocking flow through the valve, to an unseated position in which fluid flow exits the valve through radially directed passages or ports. Examples of such valves may be seen in U.S. Pat. Nos. 1,443,016; 1,626,549; and 2,937,659. In these pump valves of the prior art, the ball closure members are lifted by fluid flow and the differential pressures existing between the inlet side and outlet side of the valve. The ball is thus subjected to considerable deterioration from erosive and/or corrosive flow and from constant uncontrolled reciprocation within the valve cage. In addition, uncontrolled up and down movement of the ball closure member may damage the seating surfaces of the valve seat. Such deterioration of the ball closure member and the seat may result in fluid leakage requiring costly removal and repair procedures.
Another problem associated with pump valves of the prior art is that associated with the outward flow through the ball valve cage ports or passages as fluid flows toward the surface of the well. With the valves of the prior art, this outward flow of fluid, which may contain sand or other erosive materials, may erode the surrounding pump barrel, eventually penetrating its walls. This type of flow may also create irregular surfaces in which friction between the reciprocating plunger assembly and the surrounding barrel is so increased that undue wear and leakage may occur, substantially reducing pumping efficiencies. In either case, an expensive pulling and repair operation may be required.
Some attempts have been made to overcome the aforementioned problems of pump valves of the prior art. One example of such may be seen in U.S. Pat. No. 4,691,735. In this valve, a piston is provided for lifting the ball closure member of a pump valve off of its seat within a ball protection shield or cage above openings in the cage. This is supposed to contain the uncontrolled movement of the valve ball closure member and protect the ball from erosive fluid flow. While these characteristics of the valve appear to have been improved, this valve requires a piston member for lifting the ball valve from its seat. Thus, another component is added to the valve requiring additional length and sealing surfaces. Furthermore, the piston reduces flow through the valve by reducing flow areas and adding friction increasing ports through the piston. Obviously, additional improvements in the subsurface pump valve art are needed.