Analysis of the Motion of Plate Type Suction or Discharge Valves Mounted on Reciprocating Pistons

The equations of motion of plate type suction and discharge valves mounted on reciprocating pistons are given. Their solutions by modal series expansion are discussed and finally given in a form that conforms to the notation and approach used in previous work. Using the definition of an equivalent pressure, it is shown that both types of valves are assisted in closing, which may result in premature closing. During opening, suction valves are assisted by the piston acceleration, but discharge valves are in general not, depending on the compression ratio. It is concluded that the piston acceleration is not a negligible effect and should be included in simulation programs. INTRODUCTION Piston mounted valves are perhaps mainly useful in the refrigeration industry, where suction valves are and have been mounted on reciprocating pistons in low side compressors, where the suction gas fills the crank housing. While the author is not aware of an actual design, the same is possible in principle for discharge valves, provided the discharge gas fills the crank housing which is the case in so called high side compressors. The air and gas compressor industry faces the dHf iculty to keep air or gas from being contaminated by lubricant, and is therefore less likely to utilize such a des1gn. Piston mounted valves are attractive because of the continuing quest of designers to find enough space in the cylinder head to accommodate valve porting and plates without increasing the clearance volume unreasonably. As the compressor volume becomes larger, space restrictions become more severe. Utilizing the piston surface area almost doubles the available porting space. 257 The potential penalty one pays is undesirable valve behavior, unless one compensates for the effect of the piston motion properly. A piston mounted suction valve was first simula~ed by one of the author's students, J.M. Baum [1), as part of a Master's thesis. Unfortunately, the thrust of this simulation was directed toward the understanding of the gas pulsations in the discharge piping of a four cylinder automatic air-conditioning compressor. The suction valve had a negligible influence on it and was modeled only for completeness sake. Thus, no conclusions about the essential behavior of a piston mounted valve were drawn at the time. This paper attempts to remedy this to some extent.