McDonnell & Miller MM 286 Series 1575 Low Water Cut-Off - Manual (Page 11)

MAINTENANCE
SCHEDULE:
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.
• Inspect the probe chamber and equalizing
piping annu a l ly. Remove all sediment and
debris from chamber and/or equalizing piping.
• Inspect and clean probes. Use a non-abrasive
cloth to clean probes. Replace probes if
probes are worn, corroded or have excessive
coating of scale or rust that can not be easily
cleaned off.
Replace probes every 5 years.
More frequent replacement may be required when
s evere conditions exist such as rapid sw i t c h
cycling, surging water levels and use of water
treatment chemicals.
Replacement parts are available from your
local authorized McDonnell & Miller
Distributor. The use of parts or components other
than those manufactured by McDonnell & Miller
will void all warranties and may affect the units
compliance with listing or regulating agencies.
NOTE
More frequent blow-down may be necessary due to
dirty boiler water and/or local codes.
NOTE
The probes may need to be inspected and cleaned more
f r e q u e n t ly on systems where there is the potential of
coating build-up on the pro b e s . This includes systems:
• With high raw water make-up
• With no condensate return
• With untreated boiler water
• Where significant ch a n ges have been made to the
b o i l e r-water chemical treatment pro c e s s
• With oil in the boiler water
BLOW DOWN PROCEDURE:
When bl owing down a control at pressure, the bl ow
d own va l ves should be opened slow l y. The piping needs
to be wa rmed up and stagant water in the drain piping
needs to be pushed out. Suddenly opening a bl ow dow n
va l ve causes steam to condense, which may create
water hammer. Damage to components can occur when
water hammer occurs due to improper bl ow down piping.
For these reasons, McDonnell & Miller recommends a
dual va l ve bl ow - d own system for each control.
B l ow down the low water cut-off when the water level is
at its normal level (pump/va l ve off) and the bu rner is on.
• Open the upper “ Po s i t i ve Shut-off Ball Va l ve ” ( # 1 ) .
• S l owly open lower “Throttling Gate Va l ve ” ( # 2 ) .
• With both va l ves open, the water level will drop in
the sight glass.
• When the water falls below the level of the middle
p r o b e, the pump or va l ve should turn O N.
• When the water falls below the level of the longest
p r o b e, the bu rner should turn O F F. N OT E : The
Red LED will turn O N to indicate low water condition.
• S l owly close the lower “Throttling Gate Va l ve ” ( # 2 ) .
• The water level should begin to rise and the bu rner
should turn O N (Red LED turns off) when the level
is at the middle probe. The pump or va l ve should
t u rn O F F when the water level rises above the
s h o rtest probe postion.
• Close the upper va l ve “ Po s i t i ve Shut-off Ball Va l ve ” ( # 1 ) .
• O b s e rve that the water level returns to its normal level
b e fore leaving the 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 sequence of actions does not occur, a s
described, immediately close all valves, turn off the
boiler and correct the problem. To correct the problem,
inspection/cleaning of all probes may be required.
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