1. Field of the Invention
The present invention is directed to a multiple element poppet valve arrangement, particularly for use with gas compressors, and more specifically to a scavenger valve having multiple cage elements for multiple poppets.
2. Discussion of the Prior Art
The use of single or multiple deck multi-element valves in gas transmission compressors and the like is well known. In conventional installations, the reed or strip valve is formed by a plate-like seat having a number of spaced slots communicating with an inlet port which mates with a plate-like cage or stop, having recess which communicates with an outlet port. The slots and recesses are so arranged that they will be aligned to form a valve chamber when the cage and seat, respectively, are mated together, with the periphery of the seat area and the complementary cage area for forming a seating surface.
One common type of valve is a poppet valve having a reciprocating gating element mounted within each valve chamber. Conventionally, the poppet is mushroom-shaped and typically includes a hollow stem slidable within a counter recess in the cage bore which serves to guide the poppet during its reciprocating travel. The opposite end of the poppet is typically of a convex arcuate shape configured to form a seal with the valve seat when the valve is closed. A coil spring is usually located within the hollow valve stem and serves to bias the poppet toward the seat and toward a valve closed position.
In many such applications, the poppet valve is a scavenger valve, where intake air or gas enter the flow path through the cage or stop when the valve is closed or moving towards the closed position and positive flow passes through the valve chamber when the valve is open or moving towards the open position.
Valve assemblies using poppets movable alternately, into, and out of, engagement with the exit of a gas port for controlling flow are well known in the art. See e.g. U.S. Pat. Nos. 4,228,820; 4,489,752; 4,872,481 and 5,190,446. Examples of the use of such poppet valve assemblies are in gas compressors where, in larger models, the poppet valve assembly can include a number of separate poppet valves operating in parallel in the same valve assembly The growing necessity for energy conservation, particularly in the area of natural gas reserves, has kindled new interest in developing better ways to transport natural gas and the like more efficiently and at less cost. Generally, gas transmission facilities have relied on reciprocating compressors to move the gas through pipelines connecting the gas reserve to the intended point of use. Many of these compressors utilize poppet valves to provide suction or discharge capability. Inasmuch as these valves may experience up to one thousand closures per minute or more, any deficiency of the valve results in reduced efficiency, excessive wear and possible valve failure.
As is well understood, the poppet element or poppet is a spring-loaded mushroom-shaped pressure actuated seal which reciprocates in coaxial bores in the valve seat and the cage. In conventional valves, the poppet is guided by a stem portion in the valve cage. A spring received in a recess or counterbore in the stem serves to provide a return force for initiating the return of the poppet as well as to provide an opposing force to prevent premature and excessively rapid opening of the valve. Generally, a close fit between the poppet stem and the cage is required to provide dampening action. Such valves have historically experienced manufacturing and maintenance problems, arising from the fact that the poppet head must be accurately positioned with respect to its mating seating surface on the valve seat. Since the poppet is guided in the cage, close tolerances are required to develop the proper mechanical alignment between the seat and cage. For this reason, seats and cages must generally be maintained in matched sets or groups, which complicates routine servicing and can prevent renewal of the seat sealing surface without replacement or rework of the entire valve.
Efficiency has also been reduced in prior art valves by turbulence created by restrictions in the flow path, which leads to non-uniform flow velocities, losses and unnecessarily large pressure drops. For such compressors, it has been found that any turbulence produces resistance impeding the flow of gas leading to increased component wear an unacceptable efficiencies.