
Applies To 



Product(s): 
HAMMER 


Version(s): 
08.11.XX.XX, 10.XX.XX.XX 


Area: 
Modeling 


Original Author: 
Jesse Dringoli, Bentley Technical Support Group 

Problem
What should I enter for the "Discharge Coefficient (fully open)" for a surge anticipator valve?
How can I calculate the discharge coefficient (Cv) of a SAV?
Solution
This would typically be obtained from the Surge Anticipator Valve manufacturer. If they don't provide it, you can calculate it based on the information that you do have.
For example, for a 4 inch opening (area of 0.087266 ft^2) and assuming an orifice coefficient of 0.6. Here is the orifice equation rewritten as:
H = (Q/CA)^2/(2g)
Let's pick a flow of 1.0 cfs, which results in a pressure head (H) of (1.0 / (0.6 * 0.087266))^2 / (64.34) = 5.67 ft.
The following equation can be used to find the discharge coefficient:
Cv = ((39.693 * d^4) / ( H / (V^2 / 2g)))^0.5.
You can plug in the pressure head along with the same flow and corresponding velocity (using Q=VA) to derive the discharge coefficient:
Cv = ((39.693 * (0.33333)^4) / (5.67 / (11.456^2 / 64.34)))^0.5 =
0.41985 cfs/(ft H2O)^0.5
See Also
Modeling Reference  Surge Valves