Steam CV

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     C   o   n   t   r   o   l   V   a   l   v   e   s   G   l   o   b   e   C   o   n   t   r   o   l   V   a   l   v   e   s Steam Sizing Chart  In the interests of development and improvement of the product, we reserve the right to change the specification. Local regulation may restrict the use of this product below the conditions quoted. Limiting conditions refer to standard connections only. TI- 1-618 -US 3.03 Determining the Value Cv Cvcalculation 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 applica-tions. How To Use the Chart Example 1. To find Cv value for critical flow application.Steam Demand1500 lb/hrUpstream Pressure55 psi guage70 psi absoluteRefer to Selection Chart Opposite.1)Draw 1500 lb/hr flow line (A-B)2)Draw a horizontal line from 70 psi absolute to critical pressure dropline (C-D).At thisintersection drop a vertical line.3)At the crossing point of these two lines, read off the Cvvalue required, i.e.Cv 134)Select valve size required from the appropriate valve type technicalinformation sheet. Example 2. To find Cv value for non critical flow application.Steam Demand500 lb/hrUpstream Pressure85 psi guage100 psi absoluteDownstream Pressure65 psi quage85 psi absolute1)Draw 500 lb/hr flow line.2)Draw a horizontal line from 100 psi absoluteAt the intersection with 20 psi pressure drop, draw a vertical line.3)At the crossing point with the 500 lb/hr horizontal line read off the Cv value required, i.e.Cv 3.84)Select valve size required from the appropriate valve type technicalinformation sheet. How to Use Formula Proceed by calculating the required Cv from given flow data, havingprior determined whether the flow is critical or sub-critical.The followingequations have been adapted from the ISA S75.01 standard to allow forpractical everyday use without significant sacrifice in accuracy. For Steam ServiceFor Saturated Steam wCv=2.1 ∆ P(P1+P2) wCv=1.647 (P1)C V =Valve CoefficientP1=Upstream Pressure, psiaP2=Downstream Pressure, psia ∆ P=Pressure drop P1- P2, psiaw=Flow Rate, lb/hSubcritical FlowCritical FlowWhen ∆ Pis less thanWhen ∆ Pis greater than.81 (P 1  /2).81 (P 1  /2) This chart is forexample only. Acomplete chart forsizing is overleaf.       C   o   n   t   r   o   l   V   a   l   v   e   s   G   l   o   b   e   C   o   n   t   r   o   l   V   a   l   v   e   s Steam Capacity Chart Spirax Sarco,Inc.,1150 Northpoint Blvd,Blythewood,SC 29016Telephone:(803) 714-2000 FAX (803) 714-2222 TI- 1-618 -US 3.03    ©   S  p   i  r  a  x   S  a  r  c  o ,   I  n  c .   2   0   0   3
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