Pumps and valves are primary power and control devices in water supply piping systems. A collaborative operational scheme is very important for a series pump–valve system to decrease the transient pressure during the startup process. In order to analyze the influence of the operational time differences between the pump and the valve on the transient process, a complicated pump system was numerically simulated using the method of characteristics (MOC). The boundary conditions of the pump and the valve were separately established by equating an auxiliary element in the discrete mesh. The transient pressure, pump speed, and flow were studied for various time differences and the valve opening process for the series pump–valve startup process. Furthermore, an optimal collaborative scheme was presented to prevent inverse rotation and overpressure during the startup process. The results show that a reasonable time-lapse and fast opening can prevent the backward flow and reverse rotation, as well as control the transient maximal pressure during the system startup process.