Pressure relief valve (PRV) opens and closes automatically at a pre-set pressure to relieve excess pressure so to protect fire pump. When fire pump starts and the set pressure is exceeded, the pressure relief valve opens and a portion of the water is diverted through the auxiliary route, and the pressure inside the pipeline stops rising. Once it reaches the valve’s reseating pressure, the valve then closes. When firefighting demand slows or ceases, it diverts entire pump output to discharge, allowing fire pump to be stopped without causing surging.