When all the parallel pumps are working, the pump head is greater than the control pressure difference of the guide
valve, the guide valve is closed, and the main valve can reach the maximum opening degree. When it is necessary to change the flow rate and reduce the number of running stations, the flow rate of the pump still in operation increases, and the head is smaller than the control pressure difference of the guide
valve, when the guide valve opens, the pressure of the main valve control room increases, the main valve closes, the flow rate of the pump decreases, and the head increases accordingly. When reaching the balance state, the pump head is the control pressure difference of the pilot
valve. Due to the operation of other pumps, the main valve is closed after the check valve is closed to prevent the backflow of water.