What is the preferred method for starting reciprocating power pumps?
A. Starting a reciprocating pump with a closed discharge valve is naturally difficult due to the high torque required to overcome discharge pressure as well as accelerate the pump. For this reason, reciprocating pumps are typically started with an open bypass line from the discharge to the suction. To accomplish this, the operator manually opens a bypass valve, or a power-actuated dump valve is programmed to open automatically, which bypasses the liquid during the start and stop functions. A check valve is employed in the pump discharge line. It remains shut as long as the bypass (dump) valve remains fully or partly open (see Figure 6.47). Figure 6.47. Schematic of liquid bypass system The liquid pressure exerted on the plungers (or pistons) is largely caused by liquid mass and friction as it passes through the bypass valve and piping. When correctly sized, the bypass valve and piping cause low back-pressure. Only a relatively small torque is required while bypassing the liquid to a ta
