In the refrigeration industry particularly in the industrial refrigeration field, there remains a need to provide valving, specifically in the refrigeration evaporator configuration thereof, that opens and/or closes only part way in order to minimize, or better yet, prevent liquid hammer or vapor propelled liquid from damaging the system and causing undue piping stress.
The dual position pilot operated valve assembly of the present invention is based upon and includes the main body assembly of a known commercial gas powered suction stop valve of type CK-2 shown in Bulletin 50-12B and available from the Refrigerating Specialties Division, of the Parker Hannifin Corporation headquartered in Cleveland, Ohio, U.S.A. the CK-2 valve requires an additional solenoid of smaller capacity to be installed in parallel in order to slowly release defrost pressure from the evaporator and reduce the possibility of hydraulic shock. The noted CK-2 valve and its associated parallel solenoid suffers from the disadvantage that when an electric power failure happens to occur during a defrost cycle, the solenoids close and the main valve opens immediately, thus creating the potential for undesired hydraulic shock. While this disadvantage is also encountered in the dual position valve assembly to be described hereinafter by controlling the leakage rate around the secondary piston thereof controls the rate at which the valve assembly responds to the supply or cessation of high pressure control gas to the top of this piston. Thus, by controlling this leakage rate and/or the volume above this piston can slow the rate of response such that, incase of such a power failure the defrost cycle hydraulic hammer can be largely mitigated.
The patent literature includes a large number of valving devices that use multiple power pistons and representative ones thereof include: U.S. Pat. No. 2,596,036 to MacDougal; U.S. Pat. No. 2,745,254 to Malkoff; U.S. Pat. Nos. 2,748,571 and 2,763,130 both to Henderson; and U.S. Pat. No. 5,070,707 to Ni. However, none of these prior art structures teach or suggest the unique features of the present invention.