Calculation of Pressure Regulators for Steam   Calculating the Kv-value The selection of a valve requires first of all that the Kv-value is determined from the operating data under which the valve is to operate. As in most cases a table or diagram giving the specific volume of steam is not available, the formulae given below, which treat steam as an ideal gas, can be used to arrive at a sufficiently accurate result. for subcritical pressure drops i.e. if use formula for supercritical pressure drops i.e if use formula The temperature of steam in its saturated state ( saturated steam ) may be roughly calculated using the formula ts » ´100 Kv Flow Coefficient m³/h G Mass Flow kg/h Q1 Volume Flow Upstream of the Valve m³/h Q2 Volume Flow Downstream of the Valve m³/h p Differential Pressure ( p1-p2 ) bar p1 Inlet Pressure ( abs.) bar p2 Outlet Pressure (abs.) bar t1 Temperature at Inlet °C t2 Temperature Saturated Steam °C w1 Velocity before the valve m/s w2 Velocity behind the Valve m/s d1 Nominal Diameter before the Valve mm d2 Nominal Diameter behind the Valve mm Example: We are looking for a stainless steel pressure reducing valve capable of reducing the pressure of 1100 kg/h of saturated steam from 7 to 4 bar. The pressure drop is subcritical because , namely 3 < As we do not know either the specific volume nor the temperature, we use the formula Having calculated the temperature ts » ´ 100 = ´ 100 = 168 °C we calculate = 12,9 m³/h To the Kv-value calculated from the operating data we add an allowance of 30 % and thus obtain the minimum Kvs-value which the valve to be selected should have. Kvs-value = 1,3 x Kv-value = 1,3 x 12,9 = 16,8 m³/h continue Liquids Gases Steam   Kv-value   Kv-value   Kv-value   Nominal diameter   Nominal diameter   Nominal diameter   Valve selection   Valve selection   Valve selection download the PDF-file: Calculation of pressure regulators / PDF (156 kb)