Cla-Val 750B-4KG - Manual (Page 16)

Capacity Information
700 Series
MODEL
1
1
However, the above stated relationship only remains valid if the flowing conditions are both turbulent
(non-viscous) and non-cavitating. Fortunately, these conditions are the most common encountered in
liquid flow applications. In those cases where viscous or cavitating
(1) flow conditions are possible,
consult factory for guidance in selection of valve size.
Example:
Determine the maximum flow rate capability of a 4" Cla-Val Roll Seal valve in fresh water service with
an upstream pressure of 90 psi and downstream pressure of 77 psi. From table, a 4" Cla-Val 700
Series valve has a full open C
v
factor of 128; hence:
Valve Sizing Coefficient - C v
A very useful expression often used in determining the head loss and/or flow rate capacity of control
valves is the C
v
factor. Commonly referred to as the flow coefficient or valve sizing coefficient, this
empirically determined factor describes the flow capacity of a valve.
The C
v
factor is defined as the number of U.S. gallons per minute of water (at 60°F flowing temperature)
discharged through a flow restriction with a head loss of one psi. In the case of a control valve, the C
v
value is normally stated for the valve in the fully open position. For conditions other than full open, (i.e.
modulating valves), contact Cla-Val Technical Services.
Cla-Val 700 Series Valves - Full Open C v Factors
Liquid Flow Equation
The basic flow to pressure drop relationship for liquid service is expressed by the formula:
Q = 128 = 128 (3.61) = 462 GPM x 13 or
Q = Flow rate in U.S. gallons per minute (GPM).
C
v
= Valve sizing coefficient.
∆P = Head loss across valve in psi.
G = Specific gravity of liquid at flowing temperature referred to
water (1.0) at standard conditions (60°F).
Where:
(1) Note: For further information on cavitation, see technical data sheet "RS-Cavitation".
Q = C
v
Q = C
v
x ∆P
G
∆P or
1
G
Valve Size 2" 3" 4" 6" 8" 10" 12"
Cv Factor
48 84 128 451 764 1443 2048