Service And Repair - Honeywell VRN Notice D'installation

VRN DYNAMIC PRESSURE-REGULATING CONTROL VALVES AND ACTUATORS
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 volt-
age issued by the building automation controller.
Valves with flow control inserts have an equal per-
centage flow characteristic (See Fig. 33). 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. 33. 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 con-
firmed by pressure measurement across coil, using
coil manufacturer's data. Retighten shaft coupling.
Use Fig. 33 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.
38-00005EFS—04
FULL PORT
BALL
2-WAY
CHARACTERIZED
FLOW
40° 50° 60° 70° 80° 90°
M29551A

Service and Repair

The valve stem can be replaced in-line, if necessary. See
Fig. 34.
STEM
ASSEMBLY
Fig. 34. Replacing the valve stem in-line.
Follow steps 1 to 6 of "Mounting Plate Adjustment" on
page 3, then:
1. If the lower packing gland is stuck, remove it with
gland removal tool or rubber-tipped dental tool.
CAUTION
Avoid scratching the inside of the valve neck.
This may cause a leak when re-assembled.
2. Carefully remove any fouling or corrosion from
inside of valve.
3. Align arrow with short leg of "T" symbol on new stem
assembly.
NOTE: "T" symbol will vary.
4. Insert the new stem assembly. Be sure to line up the
stem key with the ball slot.
5. Fasten stem retainer high pressure plate to the valve
using the new countersunk screws. Then fasten the
mounting plate to the valve.
6. Repressurize valve and confirm stem does not leak
before proceeding.
7. Slide the sub shaft over the stem with the tab ori-
ented as shown in Fig. 34.
8. Replace the thermal break, shaft, and shaft cover. If
shaft has come loose from thermal break, push
firmly on end of shaft until blade in shaft snaps into
thermal break.
9. Replace actuator and secure it to shaft and mount-
ing plate.
10. Snap handle onto top of shaft.
Any other service to valve such as seat seal replacement
requires removal of valve from piping.
10
COUNTERSUNK
SCREWS
STEM RETAINER
PLATE
"T" SYMBOL
STEM
UPPER PACKING
GLAND
O-RING
LOWER PACKING
GLAND
M34994