Sterlco 2.0 Inch 518 Packed Stem Radiator Valve. Sterlco® Radiator Valve Model 518 is designed for steam heating systems. Sterling’s Radiator valves features a heavy cast brass body, brass union and nut. This solid, simple, rugged construction will resist strains during installation and assures long serviceable life. The Packed Stem is designed for heating systems with pressure of 25 in. vacuum to 125 PSI. It may also be used in water systems with pressures to 200 PSI. The 518 valve is also equipped with positive (on) or (off) control for any type of heating element or radiator. The unique features of this valve makes the product Americas Number one choice for heating applications.