Water heater 175 psi Safety Pressure Relief Valve 1/4" Water flow direction is from Male pipe to female pipe. Both connections are 1/4" national pipe Brass body with a Stainless male nipple. Install between the heater and outbound water connection. Designed to protect the heater in the event the water expanse too rapidly. Used on 90% of all portable carpet cleaning machines that have heaters on them. Other pressures available. Compares to current and past OEM associations: Nautilus PSA100901 Mytee B124 Mytee B200