How do I select a valve for a steam system?
Flowrite 599 Series valves can be used on steam systems with an inlet pressure to 100 psig, with a maximum differential pressure of 50 psi.
The goal of steam system design is to condense all of the steam in the radiator or coil, and return only liquid condensate to the boiler. Doing so capitalizes on the high energy transfer associated with fluid change of state. The coil energy transfer rate is directly proportional to the mass flow rate of steam which enters the coil; hence a linear characteristic control valve is preferred. The trim material should be selected according to the pressure drop across the valve: <25 psi, brass/bronze; <50 psi, stainless steel. Choose the packing material according to the maximum inlet steam temperature: <250°F, EPDM O-ring; <337°F, Teflon V-ring.
Most of the H.V.A.C. steam systems will use saturated steam. Some systems will use superheated steam. Most systems will be two-pipe systems. Occasionally an old one-pipe system may be encountered - condensate return is difficult in these systems and may cause water hammer. On AHU coils, Siemens Building Technologies recommends 1/3, 2/3 control to improve control at low load, and extend life of valve trim by minimizing wire drawing. Use the steam valve sizing formulae for most accurate results. This formulae can be found in the Siemens HVAC Products catalog. Remember to use ABSOLUTE pressure, not gage pressure, in all steam sizing!