Selection Guide

12 Copyright 2008 TAC All Rights Reserved. F-26752-12
Installation Considerations
Mounting Angle of Valve Assembly
Be sure to allow the necessary clearance around the valve assembly. The valve assembly must be mounted so that the valve
stem is at least 5° above the horizontal. This ensures that any condensate that forms on the valve body will not travel into the
linkage or actuator, where it may cause corrosion. On steam applications, where the ambient temperature approaches the limit
of the actuator, the valve assembly must be mounted 45° from vertical. See Actuator/Linkage Assemblies General Instructions,
F-26635 for details.
Insulation of Linked Globe Valve Assembly
The globe valve should be completely insulated to minimize the effect of heat transfer and condensation at the actuator.
Caution: The actuator/linkage must not be insulated. Doing so will result in excess heat or condensation within the actuator.
Temperature Limits for Globe Valve Assembly
When installing the globe valve assembly, observe the minimum and maximum temperature limits given in the Actuator
Specifications and Valve Assembly Mounting Dimensions section of this document.
Sizing and Selection
Two-position Control
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 Control
Proportional 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 procedure 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 (Table-6).
Secondary Circuits with Small Booster Pumps: 50% of available pressure difference (equal to the drop through load, or 50%
of booster pump head).
Table-6 Conventional Heating System.
Design Temperature
Load Drop °F (°C)
Recommended Pressure Drop
a
(% of Available Pressure)
a
Recommended minimum pressure drop = 5 psi (34 kPa).
Multiplier on
Load Drop
60 (33) or More 50% 1 x Load Drop
40 (22) 66% 2 x Load Drop
20 (11) 75% 3 x Load Drop