Apollo Valves 13-211-B15, 3/4" NPT Male x Female Side Outlet Pop Saftey Relief Valve, ASME Steam, 15 psi Set Pressure. This Apollo Valve 13-211 series steam relief valve is a safety valve for protecting small to medium low-pressure steam heating boilers. It has a cast bronze body, a 15 pounds per square inch (psi) relief pressure, a 3/4" male National Pipe Thread (NPT) inlet connection and 3/4" female NPT outlet, and a PTFE (polytetrafluoroethylene) seat. The valve's body and nozzle are bronze and the spring is steel for resistance to corrosion. The flat seat is a PTFE-faced disc for positive seal, resistance to moisture and high temperatures, and positive drainage of condensate from the seat area. The valve can be used in operating temperatures up to 250 degrees F. This relief valve is American Society of Mechanical Engineers (ASME) safety rated for Section IV heating boilers and is suitable for low-pressure steam heating and supply boilers.