Page 46 - Valve Selection Handbook
P. 46
Fundamentals 33
Because p/p 0 = specific gravity and the numerical value of Ap 0 is
unity, Equation 2-12 is normally presented in the form:
where
G = specific gravity
This relationship is incorporated in the International Standards Associ-
ation (ISA) standards S.39.1 to S.39.4 and Publication 534-1 19 of the
International Electrotechnical Commission (IEC), and applies to single-
phase and fully turbulent flow of Newtonian liquids. For other flow con-
ditions, refer to the above ISA standards, IEC Publication 534-2 Parts 1
and 2, or Reference 20.
Flow Coefficient K v
The flow coefficient K v is a version of coefficient C v in mixed SI
units. It states the number of cubic meters per hour of water at a tempera-
ture between 5° and 40°C that will flow through the valve with a pres-
sure loss of one bar at a specific opening position, as defined by the
equation:
where
3
Q = m /hour
Ap 0 = reference differential pressure = 1 bar
Ap = operating differential pressure, bar
3
Po = density of reference fluid (water = 1,000 kg/m )
p = density of operating fluid, kg/m 3
Because p/p 0 = specific gravity and the numerical value of Ap 0 is
unity, Equation 2-14 is normally presented in the form:
