Civil Engineering Reference
In-Depth Information
Fig. 26-16.
Combining flow—branch angle 30
—loss coefficient
K
23
(
Source:
Reference 7; cour-
tesy of the BHR Group Limited)
where:
Q
flow rate, gallons per minute.
p
pressure drop across the valve, psi
C
v
flow coefficient
The conditions desired to be controlled are usually well defined. The flow rate range
that the user wishes to control and the variation in upstream and downstream water
level that will be experienced can be defined. From these known conditions, the range
in
C
v
values are calculated. The range of calculated
C
v
values then are compared to
the
C
v
values for various valve sizes to enable the user to select the appropriate valve
size.
If the control valves are going to dissipate a high head, then cavitation may be
experienced. Care must be taken to avoid operation of valves under conditions of
cavitation.
