The fixed displacement pump shown in Fig. 4.3 delivers 20 GPM continuously. The relief valve is set on 2500 psi. When the DCV is manually shifted, the pump builds pressure to 1300 psi, and the load begins to move. At this point, the operator notices that the load is moving too fast. Remember, the required flow is only 9 GPM, and the pump is delivering 20 GPM. The operator partly closes the DCV, thus creating a restriction. The operator continues to close the valve manually until the restricted flow gives the desired load speed. The restriction produced by partly closing the DCV builds pressure at the relief valve to the point where it opens sufficiently to dump 11 GPM back to the reservoir. This flow is dumped at some pressure less than 2500 psi, the full open position of the relief valve. To produce the graph at the bottom of Fig. 4.17, we assume that the 11 GPM is dumped at 2500 psi.
Total system capacity is compared to the required capacity in the power diagram shown at the bottom of Fig. 4.17. The power loss for the open circuit is
