Steam Sizing Chart - Spirax Sarco International

1 ControlValvesGlobe ControlValvesSteam Sizing ChartIn the interests of development and improvement of the product, we reserve the right to change the regulation may restrict the use of this product below the conditions quoted. Limiting conditions refer to standard connections the Value CvCvcalculation is an interactive process requiring knowledge of valvedynamics, piping geometry factors, and outlet velocities. In practice, thissizing Chart is based on emperical values and will cater for most To Use the ChartExample find Cv value for critical flow Demand1500 lb/hrUpstream Pressure55 psi guage70 psi absoluteRefer to Selection Chart )Draw 1500 lb/hr flow line (A-B)2)Draw a horizontal line from 70 psi absolute to critical pressure dropline (C-D).

2 At thisintersection drop a vertical )At the crossing point of these two lines, read off the Cvvalue required, Cv 134)Select valve size required from the appropriate valve type technicalinformation find Cv value for non critical flow Demand500 lb/hrUpstream Pressure85 psi guage100 psi absoluteDownstream Pressure65 psi quage85 psi absolute1)Draw 500 lb/hr flow )Draw a horizontal line from 100 psi absoluteAt the intersection with 20 psi pressure drop, draw a vertical )At the crossing point with the 500 lb/hr horizontal line read off the Cv value required, Cv )Select valve size required from the appropriate valve type technicalinformation to Use FormulaProceed by calculating the required Cv from given flow data, havingprior determined whether the flow is critical or sub-critical.

3 The followingequations have been adapted from the ISA standard to allow forpractical everyday use without significant sacrifice in Steam ServiceFor Saturated SteamwCv= P(P1+P2) wCv= (P1)CV= Valve CoefficientP1 = Upstream Pressure, psiaP2 = Downstream Pressure, psia P = Pressure drop P1- P2, psiaw= Flow Rate, lb/hSubcritical FlowCritical FlowWhen P is less thanWhen P is greater (P1/2).81 (P1/2)This Chart is for example only. A complete Chart forsizing is overleaf. ControlValvesGlobe ControlValvesSteam Capacity ChartSpirax Sarco , Inc., 1150 Northpoint Blvd, Blythewood, SC 29016 Telephone: (803) 714-2000 FAX (803) 714-2222TI-1-618-US Spirax Sarco , Inc.

4 2003