Contact US



flow coefficient
Flow Coefficient, Cv factor 
 
A Cv factor (C-sub-V) is a numerical expression associated with the number of gallons of water per minute that will pass through a valve with a 1psi differential between the valve's inlet and outlet.
 
It can be calculated by the formula:  Cv = Q/22.8 * Ö{(T1*G)/(DP(P2+Pa))}
Where:
Cv = capacity coefficient
Q = required flow in standard cubic feet per minute (scfm) at 14.7psig, 36% relative humidity
G = specific gravity of the flowing medium (G = 1 for air)
T1 = absolute temperature (460 + degrees F)
P1 = inlet pressure (psig)
P2 = outlet pressure (psig)
DP = pressure drop (psi) static to static pressure
Pa = atmospheric pressure (psia)
 
A simpler alternative is the formula:  Cv = flow rate (scfm) * A (constant from table below)
 
5psi is the maximum desired pressure drop across a solenoid valve that is used for compressible fluids such as air.
For EXAIR's standard testing conditions of 80psi and a maximum 5psi pressure drop across a valve, the A constant is 0.048
In sizing a valve to use for a particular application, the valve must have a Cv value equal to or higher than the calculated Cv value based on the required air flow volume, inlet pressure, and pressure drop across the valve.
 
 

Inlet Pressure

"A" Constants for Various Pressure drop

2 psi

5psi

10psi

10

.155

.102

-

20

.129

.083

.066

30

.113

.072

.055

40

.097

.064

.048

50

.091

.059

.043

60

.084

.065

.040

70

.079

.050

.037

80

.075

.048

.035

90

.071

.045

.033

100

.068

.043

.031

110

.065

.041

.030

120

.062

.039

.029

130

.060

.038

.028

140

.058

.037

.027

150

.056

.036

.026

160

.055

.035

.026

170

.054

.034

.025

180

.052

.033

.024

190

.051

.032

.024

200

.050

.031

.023

 

 

 

 

Category
 
Last modified at 11/14/2008 11:23 AM by emilymortimer@exair.com
QUICK ORDER:
CART INFORMATION:
APPLICATION SEARCH:
 
 
 
 
 
Bookmark and Share
 
  Follow Us
  RSS Wordpress Twitter Facebook