VRN PRESSURE INDEPENDENT CONTROL VALVES AND ACTUATORS
38-00032—01
12
Application Notes
IMPORTANT
Valve sizing is important for correct system
operation. Undersized valves do not have sufficient
capacity at maximum load. Oversized valves do not
have sufficient authority over the load in
modulating applications.
Oversized valves can cause excessive cycling and
the seat and ball can be damaged because of the
restricted opening.
Proper Use
These valves are only for use in cold, warm, and hot water
systems. Not suitable for oil, combustible gases, or steam.
They are designed for a medium temperature range of from
35 to 250°F, at a maximum pressure of 360 psig VRN
valves are to be operated with the appropriate Honeywell
direct coupled actuators only.
Water should be properly filtered, treated and conditioned
according to local conditions and the recommendations of
the boiler or chiller manufacturers. The installation of a
strainers and filters is recommended.
IMPORTANT
The presence of excessive iron oxide (red rust) in
the system voids the valve warranty.
Effective Flow Rate
The built-in differential pressure regulator makes fluid flow
through the valve independent of changes in supply
pressure, eliminating “hunting” by the control system, even
at low coil flow. The pressure regulator virtually eliminates
cavitation in the valve, and decouples the control valve
from the effects of piping components such as reducers
and elbows.
Pressure independent control valves are sized to match
design coil flow regardless of coil size. VRN2 valves
eliminate the need to balance the system for proper flow,
and allow chillers to be operated at design temperature
differential for maximum efficiency at every load condition.
When used in a system with variable speed pump drives,
3-way valves and coil bypass lines are not required. In new
construction, VRN2 valves perform better than reverse
return piping designs without the extra materials these
systems need. Pressure-independent control requires less
flow, enabling use of smaller piping, pumps, and chillers.
Flow Characteristics
The VRN2 two-way dynamic pressure-regulating control
valves have:
• an equal percentage flow characteristic with
characterized flow control insert.
Required Operating Torque
Both Honeywell non-spring return MVN and spring return
low torque direct coupled actuators can be utilized with the
VRN2 valves. VR valves use a patented seat design that
reduces the torque needed from the actuator.
Table 9. Close-off, Differential Pressure Ratings.
TYPICAL SPECIFICATIONS
Valve Actuator
Actuator shall accept analog modulating [(0)2-10 Vdc],
floating (tri-state), or two-position signal as indicated in
the control sequence. Actuators shall be manufactured by
Honeywell. Actuator shall provide minimum torque
required for full valve shutoff position. Wiring terminals
shall be provided for installation to control signal and
power wiring.
Actuator shall be available with housing suitable for
outdoor installation.
Accessories Identification tags shall be available for all
valves.
Pressure Independent Valve
Valve housing shall consist of forged brass rated at no less
than 360 psi at 250°F. Standard valve ball shall consist of
chemically nickel-plated brass. Manufacturer shall be able
to provide optional 316 stainless steel ball and stem. The
valve shall have an integral differential pressure regulator
to maintain constant pressure drop across valve seat to
decouple valve flow from system pressure changes. Flow
control accuracy shall be +/-5% or better. Regulator will be
constructed from 316 stainless steel with a rolling
diaphragm and operate under positive pressure. Regulator
shall be located above axis of pipe with ¼” ISO test port
fittings to allow pressure measurement and venting.
Valve stem assembly shall be of a pack-less design and be
field-replaceable without removing the valve body from the
piping. Teflon™ seals shall hold the stem in alignment, and
protect the O-ring from system temperature fluctuations.
Stem O-ring shall be made of peroxide-cured EPDM and
be isolated from system treatment chemicals by a reservoir
of silicon grease. Valve shall have a blow-out proof stem
with minimum 600 psi rating.
Valve Type
Valve Size
Close-off
Pressure Rating
(psi)
2 way
1/2 in., 3/4 in.
100
1 in., 1-1/4 in., 1-1/2 in. 100