American Can Company Water Control Valve Sizing For Steam Desuperheater

Example Hand Calculation

1. Water Properties a. Pressure: 325 psig (339.696 psia) b. Temperature: 217 F c. Specific Volume: 0.01684 ft3/lb d. Density: 59.3824 lb/ft3 e. Specific Gravity: 0.9529 f. Volume Flow: 15.27 gal/min g. Mass Flow: 7272.56 lb/hr

2. Type of Control Valve is Cage

3. Recovery Factor For A Cage Valve: xt = 0.75

4. Determine the Valve C1 Factor C1 = 40 ( xt )0.5 = 40 (0.75)0.5 = 34.64

5. The Control Valve Pressure Drop is 60.00 psi

6. Determine the Valve Cv Factor Cv = GPM x ( Specific Gravity/Pressure Drop psi)0.5 Cv = 15.27 gal/min x ( 0.9529/60)0.5 Cv = 1.9243

7. Determine the Valve Cg Factor Cg = C1 x Cv Cg = 34.64 x 1.9243 Cg = 66.6578

8. Determine The Pressure at the Vena Contracta Pvc Recovery xt = Pdischarge - Pvc = 0.75 = 265 psig - Pvc Pinlet - Pvc 325 psig - Pvc Pvc = 85.00 psig

9. What is the Control Valve Size

To determine the control valve size we need to look for a control valve that has a Cv = 1.9243 when the control valve is around 60 % open for good control with a equal percentage flow control. You can find the Valve Size by looking in a Manufacturers Control Valve Book for a Cage Valve with a Cv = 1.9243 @ 60 % open. Below is an approximate equation to identify the valve size:

a. Rough Rule of Thumb:

Cv = (Control Valve Body Size Inches) x (Control Valve Body Size Inches) x 12 1.9243 = (Body Size)2 x 12 Body Size = (1.9243 x 12)0.50 = 0.400 inch

This would indicate that the control valve may be around a inch valve.