Xylem MM 251C Series 750B-C3 Chamber with 3 Probes Series 750B-C4 Chamber with 4 Probes - Manual (Page 4)

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.
MAINTENANCE
SCHEDULE:
• Blow down control as follows when boiler is
in operation.
– Daily if operating pressure is above 15 psi (1 bar)
– Weekly if operating pressure is below 15 psi (1 bar)
NOTE: More frequent blow-down may be neces-
sary due to dirty boiler water and/or local codes.
• Remove and inspect probes annually. Replace
probes if they are worn, corroded or have an
excessive coating of scale or rust.
• Inspect the chamber and equalizing piping
annually. Remove all sediment and debris.
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 con-
dense, 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.
Proper Blow-down Procedure:
(Using dual valve system)
1. With water in the boiler at its normal level, open
“Positive Shut-off Ball Valve”.
2. Open “Throttling Gate Valve” slowly until drain
piping 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
the pump contacts have closed and the burner
contacts have opened thus shutting down the boiler.
Note: If this does not happen, immediately close
all valves, turn off burner and correct the problem.
4. Close “Positive Shut-off Ball Valve”.
5. Observe that the water level returns to its normal
level before leaving site.
DUAL
VALVES
FOR
BLOW
DOWN BALL VALVE
GATE VALVE
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
Replace probe every 10 years. More frequent
used in locales
required, or in appli-
replacement of the probe is required if it is
significant water treatment is
high make-up water requirements.
! CAUTION
! CAUTION
Replace Probe if:
!
NOTE
Clean probe by wiping with non-abrasive cloth and
rinsing with clean water.DO NOT use sharp instruments
to remove any accumulations of rust or scale.
PFA insulator is cracked or worn.
Probe is loose.Failure to follow this caution could
cause property damage,personal injury or death.
•
•
Replace the control every 15 years. •
•
© 2013 Xylem Inc. MM-251C July 2013 Part No. 210016
where
cation with