Tabla de contenido
Idiomas disponibles
Idiomas disponibles
3. If the control scheme requires fail-safe operation,
ensure that, upon removal of power, the fail position
coincides with the control sequence.
4. Spring return actuators are factory-configured for nor-
mally-closed, fail-safe operation on power loss. To
change this action to normally-open, remove and rein-
stall the actuator in the opposite orientation as follows:
a. Loosen the shaft coupling bolt using a 10 mm
wrench.
b. Loosen all other mounting bolts connecting the actu-
ator to the mounting bracket, and set aside.
c. Remove the actuator from the valve shaft.
d. Move the Self-Centering Shaft Adaptor to the oppo-
site side of the actuator, as displayed in Fig. 22.
Fig. 22. Change actuator to normally open.
(1) Remove the retainer clip from the Self-Centering
Shaft Adapter and set it aside for later use.
(2) Remove SCSA from actuator.
(3) Reinstall SCSA on the opposite side of the actu-
ator, aligning it based on the stroke labeling.
(4) Replace the retainer clip on the shaft coupling
using the groove of the coupling.
e. Reconnect the actuator to the valve mounting
bracket by replacing the screws previously removed
(step b).
f.
Tighten the shaft coupling bolt using a 10 mm
wrench or socket.
Operation
The differential pressure regulator maintains constant
pressure drop across the valve seat through a wide range of
head pressures. At a given ball position, flow through the
valve will be constant as defined by the formula:
where ρ is the density of the glycol mix.
P
changes constantly in a multi-zone system as other valves
IN
open and close, changing system flow and head pressure
according to the characteristics of the supply pump curve.
Reaction of the mechanical pressure regulator is
instantaneous, eliminating changes in room temperature due
to changes in fluid flow, and reducing the need for the control
system to constantly operate the control portion of the valve to
correct for the non-load related temperature changes that
occur in a system with standard control valves.
VRN DYNAMIC PRESSURE-REGULATING CONTROL VALVES AND ACTUATORS
Fig. 23. VRN2 cross section showing fitting, control ball,
At full flow in a 2-position control application, a VRN2 behaves
as a flow limiter.
M27714
The pressure regulator takes a minimum pressure to operate,
and has a maximum differential regulation capability. See Fig.
24. The high pressure drop across a VRN2 Valve is
comparable to the pressure drop across a control valve and
balancing valve in a conventional system design.
FLOW
RATE
(GPM)
SETTINGS AND ADJUSTMENTS
At the full open position, VRN2 valves will maintain flow in the
loop. Flow rates are listed in the Specification Data form 62-
3115EFS. Under steady state operation, the control system
will only require the valve to open enough to satisfy load
conditions. During morning recovery from night setback, the
controller will usually command the valve to 100%. For
optimum performance, choose only the next larger valve size
needed to satisfy design load. Do not oversize valves—
reduced rangeability and may result in less accurate
temperature control.
Ball valves close between 10 and 15% of stroke, to ensure full
seal engagement. If desired, modulating actuators can be set
to 0-10 V response so that 2 V of a 2-10 V control signal more
closely corresponds to minimum flow. The valve will still close
with signal loss.
7
and pressure regulator.
12
10
8
6
4
0
5.8
8
12
16
22
DIFFERENTIAL PRESSURE (PSID)
Fig. 24. Pressure regulation, large body models.
M29908A
100% OPEN
80% OPEN
60% OPEN
40% OPEN
20% OPEN
28
34
40
50
60
M29707A
38-00005EFS—02
Tabla de contenido
