Settings And Adjustments; Vrn2 Cross Section Showing Fitting, Control Ball, Pressure Regulator; Pressure Regulation, Large Body Models; Typical Flow Characteristics - Honeywell VRN Series Manual

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.
Fig. 29. VRN2 cross section showing fitting, control ball,
and pressure regulator.
At full flow in a 2-position control application, a VRN2
behaves as a flow limiter.
The pressure regulator takes a minimum pressure to
operate, and has a maximum differential regulation
capability. See Fig. 30. 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.
12
10
8
FLOW
RATE
6
(GPM)
4
0
5.8 8 12 16 22
DIFFERENTIAL PRESSURE (PSID)
Fig. 30. Pressure regulation, large body models.

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
VRN PRESSURE INDEPENDENT CONTROL VALVES AND ACTUATORS
M29908A
100% OPEN
80% OPEN
60% OPEN
40% OPEN
20% OPEN
28 34 40 50 60
M29707A
19
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.
If desired, maximum flow may be trimmed to a lesser value
in one of two ways:
1. With modulating actuator, limit span of control
voltage issued by the building automation controller.
Valves with flow control inserts have an equal
percentage flow characteristic (See Fig. 31). Each
10% reduction in maximum control voltage will
result in a 10% reduction in flow.
100%
80%
60%
FLOW
40%
20%
0%
0° 10° 20° 30°
VALVE STEM STROKE
Fig. 31. Typical flow characteristics.
2. To mechanically limit stroke, set DCA to full open
position. Loosen shaft coupling and rotate valve
shaft to desired maximum flow position, as
confirmed by pressure measurement across coil,
using coil manufacturer's data. Retighten shaft
coupling. Use Fig. 31 as a guide to setting actuator
stroke.
If using mechanical adjustment technique with
MN/MS7505 modulating actuators, the stroke
auto-adaption feature will automatically scale the
2–10 Vdc signal to the mechanical rotation of the
ball. See actuator literature for details.
Coil flow can be confirmed by reading pressures at the coil
inlet and coil outlet (not across control valve as with
conventional balancing—this pressure drop will be
constant), and using the manufacturer's data to calculate
flow.
Note that the pressure regulator in this valve guarantees
that the flow through the coil will not be affected by
upstream changes in pressure. Unlike conventional
balancing valves, it is not necessary to reconfirm coil flow
after adjusting other valves. Any overflow during morning
recovery due to oversized pressure regulated valves will not
affect other valves in the system, provided pumps are
capable of required flow.
FULL PORT
BALL
2-WAY
CHARACTERIZED
FLOW
40° 50° 60° 70° 80° 90°
M29551B
38-00032—01