Pressure relieve valve
The main purpose of a pressure relieve valve is to make sure, that the system pressure does not exceed a certain limit. The tank connection, often called “Port B”, should have a low resistance for the case that the valve opens. The valve normally consists of a compressed spring that exerts a force onto a plate which in return hinders the fluid to flow from the inlet to the outlet. If the fluid pressure gets high enough, the counterforce is higher than the spring force and the valve opens.