Xylem MM 110C Series PFC 1G PFC 1GR Modulating Pneumatic Liquid Level Controls - Manual (Page 6)

SCHEDULE:
• Blow down control weekly to verify operation.
When this control is used as a boiler control,
blow down control as follows when boiler is in
operation
-Daily if operating pressure is above 15 psi.
-Weekly if operating pressure is below 15 psi.
• Disassemble and inspect annually.
Replace the controller if it is worn, corroded,
or if components no longer operate properly.
• Inspect the float, chamber and equalizing piping
annually. Remove all sediment and debris.
• Replace control every 15 years.
More frequent replacement may be required when
severe conditions exist.
NOTE
More frequent blow-down may be necessary
due to dirty boiler water and/or local codes.
Troubleshooting
Shipment may cause the control to lose calibration. If
erratic operation is observed:
a. Check position of yoke movement relative to tube
tower magnet movement.
b. Position the clamp screw even with the rib of the
mechanism housing.
c. Perform ADJUST AIR OUTPUT procedure after
any changes to mechanism.
Too much vibration of the control or float or rapid level
changes may cause the magnets to disengage,
resulting in a loss of output control. Manually re-
engage the magnets by slowly moving the yoke
through its entire range of motion until the magnets re-
engage. If re-engagement does not occur, the float
and internal magnet assembly may be damaged.
Removal of the head from the chamber would then be
required to correct the condition.
Internal (Wetted) Parts Dirty
The internal parts can operate improperly if dirt, scale
or rust is allowed to build. This condition can be a
result of not blowing down the control as recommend-
ed and/or improper boiler water chemical treatment.
Float is Crushed
Crushed floats are typically caused by improper blow-
down. Drain piping from blow-down valve to drain
should be checked for proper pitch and the blow-down
procedure followed when blowing down the control.
Purchase and install a new float ball after investigat-
ing and correcting the problem.
Float is Filled with Water
The seam weld on the float can sometimes deterio-
rate. This can be caused by the type of chemical treat-
ment used in the boiler. While this is a rare occur-
rence, the chemical treatment supplier should be con-
sulted to determine if a reaction could occur.
Purchase and install a new float after investigating
and correcting the problem.
MAINTENANCE PROCEDURE
When blowing down a control at pressure, the blow-
down valve should be opened slowly. The piping needs
to be warmed up and stagnant water in the drain piping
needs to be pushed out. Suddenly opening a blow-down
valve causes steam to condense, which creates water
hammer. Damage to components can occur when water
hammer occurs due to improper blow-down piping.
For these reasons, McDonnell & Miller recommends
a dual valve blow-down system for each control.
1. With water in the boiler at its normal level, open
“Positive Shut-off Ball Valve”.
2. Open “Throttling Gate Valve” slowly until drain pip-
ing heats up and then open fully. Observe that the
water level starts falling in the gauge glass.
3. Close “Throttling Gate Valve” after verifying that
controlled air valve opens fully.
4. Close “Positive Shut-off Ball Valve”.
5. Observe that the water level returns to its normal
level before leaving site.
To prevent serious personal injury from steam pipe
blow down, connect a drain pipe to the control
opening to avoid exposure to steam discharge.
Failure to follow this caution could cause
personal injury.
!
CAUTION
NOTE
If this does not happen, immediately close all
valves, turn off burner and correct the problem.
McDonnell & Miller
Xylem Inc.
8200 N. Austin Avenue
Morton Grove, Illinois 60053
Phone: (847) 966-3700
Fax: (847) 965-8379
www.xyleminc.com/brands/mcdonnellmiller
McDonnell & Miller is a trademark of Xylem Inc. or one of its subsidiaries.
© 2013 Xylem Inc. MM-110C July 2013 Part No. 210552