How to Size Steam Valves (Valve Sizing Tool)

Steam valves can be sized either to high pressure or low pressure condition. Typically the steam valve sizing applications assume high pressure condition. In high pressure condition (also often called as critical velocity based valve sizing) the users need to supply only Absolute Inlet Pressure (gauge pressure + 1 bar) and Mass Flow (kg/h).

In practice high pressure based calculation assumes that the pressure drop through the valve approaches 50% of the absolute inlet pressure. If the valve pressure drop is further increased i.e. smaller valve is chosen, the steam flow will reach critical velocity. When critical velocity is reached, the maximum flow rate cannot be any further increased.

On the other hand if too big valve is chosen (small pressure drop), then as the valve closes, there will be no appreciable reduction in flow until the valve is nearly closed.