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101F-27855-10 101F-27855-10
Additional Water Valve Sizing
Information
• CA-27 3-Way Valves
Application Information
• Valve Selection Table Water,
F-11080
For more information, download
these documents from our website.
3-Way Valve Sizing for Water
Proportional 3-Way Valves
Recommended Pressure Drop - Bypass Application: 50% of “available
pressure,” or equal to pressure drop through the load at full flow.
3-Way valves in the return used to control output by throttling water
flow to the load (bypass applications) are controlling output in the
same manner as throttling 2-Way valves, and must be selected us-
ing the same high pressure drops if good control results are to be
obtained.
Recommended Pressure Drop - Constant Flow Applications: 20% of
“available pressure,” or equal to 1/4 of the pressure drop through the
load at full flow.
3-Way valves used with individual pumps to control output by varying
water temperature to the load (constant flow applications) are control-
ling output by mixing two water sources at different temperatures and
do not require high pressure drops for good control results.
Water Capacity Graph Instructions
To select the appropriate valve Cv from the Graph:
1. Select the required flow from the “Flow in GPM” axis.
2. Select available pressure drop from the “Pressure Drop in psi” axis.
3. Select the appropriate line and follow to the Capacity Cv (Kv) listing
and choose the closest valve Cv flow coefficient.
4. Confirm the selection by calculation from the water equations.
Sizing for Water
Two-Position
Two-position control valves are normally selected “line Size" to keep
pressure drop at a minimum. If it is desirable to reduce the valve
below line size, then 10% of “available pressure” (that is, the pump
pressure differential available between supply and return mains with
design flow at the valve location) is normally used to select the valve.
Proportional and Floating
Proportional and floating control valves are usually selected to take
a pressure drop equal to at least 50% of the “available pressure.” As
“available pressure” is often difficult to calculate, the normal proce-
dure is to select the valve using a pressure drop at least equal to the
drop in the coil or other load being controlled (except where small
booster pumps are used) with a minimum recommended pressure
drop of 5 psi (34 kPa). When the design temperature drop is less than
60°F (33°C) for conventional heating systems, higher pressure drops
across the valve are needed for good results.
Conventional Heating System Pressure Drops
Design Temperature
Load Drop °F (°C)
Recommended
Pressure Drop (% of
Available Pressure)
Multiplier on Load Drop
60 (33) or more 50% 1x Load Drop
40 (22) 66% 2x Load Drop
20 (11) 75% 3x Load Drop
Reducer Affects
On full flow bodies, offset the affects of directly connected reducer(s)
by choosing flow coefficients 6% or more higher.
Cv (Flow Coefficient) Determination
The valves’ water capacity is based on the following formula:

∆P
or C
v
= GPM
C
v
=
GPM
∆P
Where:
C
v
= Coefficient of flow
C
v
is defined as the flow in GPM with ∆P = 1 psi with the valve
completely open
GPM = U.S. gallons per minute (60°F, 15.6°C)
∆P = Differential pressure in psi (pressure drop)
5. VB-8/9000 Globe Valves
Sizing and Selection
5. VB-8/9000 Globe Valves
Sizing and Selection