【正文】 ses of the fluid. In particular, two valveplate geometries are pared to show that alterations in the valveplate design can cause differences in the operating efficiency of the pump. In this paper, a standard valveplate design which utilizes slots is pared to a trappedvolume design which eliminates the slots altogether. In the analytical result of this paper, it may be shown that the standard valveplate design introduces a volumetric loss which may be accounted for by the uncontrolled expansion and pression of the fluid that occurs through the slots themselves. By eliminating these slots, and utilizing a trapped volume design, it may be shown that improvements in the operating efficiency can be achieved. Though this paper does not claim to provide the ideal valveplate design for all pump applications, it does provide the theoretical reason for utilizing trapped volumes and lends general insight into the overall problem of valveplate design. To make plots of the previous results as they vary with pressure, a new valve plate needs to be designed for each operating pressure. Figure 8 illustrates the changing valveplate designs as they vary with operating pressure for the basic pump parameters given in the ~40! and ~43! describe the power losses of the standard design and the trappedvolume design respectively. These equations are plotted in Fig. 9 using the parameters given in the Appendix. As shown in Fig. 9, the power losses are greater for the standard design as pared to the trappedvolume design. This fact may be explained by the slots on the valve plate. The reader will recall that the slots are used to provide a flow passage which acmodates the pressure transitions at top and bottom dead centers. At bottom dead center, when the piston is entering the discharge port, fluid flows through the valveplate slot into the piston chamber until the fluid pressure within the piston chamber is equal to that of the fluid pressure in the discharge port of the pump. In order to make these pressures equal, the fluid in the piston chamber needed to be pressed。3p/2. In this location, the piston chamber is moving from the intake port into the discharge port. In the design of Fig. 4, the slot at topdead center is designed to provide a constant flowarea into the intake port, At , and the slot length is given by the angular dimension, j t . Similarly, at bottomdeadcenter, the slot is designed to provide a constant flowarea into the discharge port, Ab , and the slot length is given by the angular dimension, j b . The valve plate shown in Fig. 4 provides, essentially, four different regions to be considered in the pressure and flow analysis for a single pistonchamber within the pump. These regions may be characterized by Table 1. Table 1 Standard value slate regions Region Angular Position Pressure Conditions Flow Conditions The pressure within the piston chamber is at discharge pressure. The discharge flow is equal to the displacement of the piston. The pressure within the piston chamber is between discharge pressure and intake pressure. The discharge flow results from the uncontrolled expansion of the fluid through the slot. The pressure within the piston chamber is at intake pressure. The intake flow is equal to the displacement of the piston. The pressure within the piston chamber is bet