Honeywell VP531A Fiche Technique page 3

TROUBLESHOOTING
Equipment Required
The following are available from Honeywell:
— 14003519-001 Add-a-Gage Kit, 0 to 30 psi (0 to 207 kPa).
— MQP852 (CCT852) Pressure Bulb.
Procedures
Sticking Stem or Leakage Around Stem
If there is evidence of a sticking stem or any signs of leakage
around the stem observed during valve operation,
disassemble, clean, and repack the valve. Also replace the
stem and disc holder assembly if it is worn. See Fig. 5 for
parts.
No Flow Through Valve
1. Check thermostat for proper operation. Measure
branchline pressure for changes with a pressure gage
as the thermostat setpoint is adjusted. If the pressure
does not change in relation to the adjustment made,
refer to the specific thermostat service data sheet.
2. Check the supply system to the valve.
a. Water Systems:
(1) Are supply pumps running? Turn on if required.
(2) Is the piping air locked? Bleed if required.
b. Steam systems:
(1) Is supply pressure adequate? Check that the
supply pressure is correct.
(2) Is steam trap functioning correctly? Service or
replace if faulty.
Uncontrolled Flow Through Valve
1. Set thermostat setpoint alternately to settings above
and below ambient temperature. If branch pressure
does not change as the thermostat setpoint is adjusted,
disconnect tubing at top of actuator and check for a
leaking diaphragm as follows:
a. Attach a gage and pressure bulb to the actuator.
b. Attempt to pump the actuator up to 13 psi (90 kPa).
Inability to maintain pressure indicates a leaking
diaphragm and requires replacing the complete top
assembly.
c. If actuator can maintain 13 psi (90 kPa) pressure,
but pressure drops when the tubing is reconnected,
look for an air leak at the: valve fitting, control air
tubing, or thermostat. Repair leak if required.
2. If everything appears normal at the valve location, but
the valve stem remains open:
a. Check the water supply and return pressures to
determine if differences exceed the valve close-off
rating. For steam, supply pressure cannot exceed
close-off rating. Adjust system pressure if required.
b. If supply and return pressures are within the limits
but a constant flow persists, check for a defective
valve seat or plug, or the possibility of a foreign
object in the valve, preventing the plug from seating.
The valve must then be disassembled. If the valve
seat is found defective, replace the complete valve
assembly. Valve disassembly or replacement
requires shutting down the system.
VP531A,C PNEUMATIC TERMINAL UNIT VALVE
REPAIR
Equipment Required
— Thin, open-end wrench (1-1/4 in. Wrench for solder body
valves).
— Commercial cleaning solvent.
WARNING
Permanent Injury Hazard
Careless handling of solvents can cause
permanent injury to the respiratory system and
skin tissue.
Use solvents in a well ventilated area. Avoid prolonged
inhalation of solvents and/or contact with the skin.
Packing Replacement
1. Remove system air and water pressure. Disconnect
tubing from barb connector on top of actuator.
2. Unscrew valve bonnet nut from valve body (Fig. 5)
using a flat, open-end wrench and remove the entire top
and insert assembly.
3. Remove the retainer from the side of the cover, twist top
counterclockwise and lift off.
4. Remove spring retaining cup and main spring by sliding
cup to disengage stem from captive slot.
5. Unscrew bonnet nut from bonnet. Remove stem and
disc holder assembly. Use stem to push out the packing
spring, old packing, and packing spacers upwards from
the bonnet.
6. Inspect stem for scoring or bent condition. Check plug
and disc holder and valve seat. Replace stem and disc
holder assembly if damaged. If the seat is defective,
replace the complete valve.
7. Thoroughly clean bonnet and valve stem with
recommended cleaning solvent. (See "Inspection and
Cleaning" on page 2.)
8. Reassemble all parts using fresh lubricant and new
packing. (See "Parts List" on page 4.)
9. Restore air and water pressure to system and perform
operational check. (See "Operational Check" on
page 2.)
Top Assembly Replacement
1. Remove air pressure to actuator and disconnect tubing.
2. Remove cover and rotate top assembly counterclock-
wise to disengage it from the base. Lift off top assembly.
3. Install replacement unit.
4. Reconnect tubing to actuator and restore system air
supply.
Diaphragm Replacement
Repair defective diaphragm by replacing the complete top
assembly. (See "Top Assembly Replacement" on page 3.)
Stem and Disc Holder Replacement
Use the same procedure as in Packing Replacement.
3 75-7251EF