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Idiomas disponibles
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VRN DYNAMIC PRESSURE-REGULATING CONTROL VALVES AND ACTUATORS
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 char-
acteristic (See Fig. 25). Each 10% reduction in maxi-
mum control voltage will result in a 10% reduction in
flow.
100%
80%
60%
FLOW
40%
20%
0%
0°
20°
30°
10°
VALVE STEM STROKE
Fig. 25. Typical flow characteristics.
2. To mechanically limit stroke, set DCA to full open posi-
tion. Loosen shaft coupling and rotate valve shaft to
desired maximum flow position, as confirmed by pres-
sure measurement across coil, using coil manufac-
turer's data. Retighten shaft coupling. Use Fig. 25 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 litera-
ture 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—02
FULL PORT
BALL
2-WAY
CHARACTERIZED
FLOW
60°
90°
40°
50°
70°
80°
M29551A
Service and Repair
The valve stem can be replaced in-line, if necessary. See Fig.
26.
STEM
ASSEMBLY
Fig. 26. 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 oriented
as shown in Fig. 26.
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 mounting
plate.
10. Snap handle onto top of shaft.
Any other service to valve such as seat seal replacement
requires removal of valve from piping.
8
COUNTERSUNK
SCREWS
STEM RETAINER
PLATE
"T" SYMBOL
STEM
UPPER PACKING
GLAND
O-RING
LOWER PACKING
GLAND
M34994
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