CleaverBrooks FLX Operation, Service And Parts Manual page 93

Inspection and Maintenance
when the blow down valve is open allowing water to drain
from the control. The test-n-check valves permit testing of the
control without draining the entire system therefore allowing
regularly scheduled verification of float style low water
cutoff.
Low Water Controls (Steam Boilers)
The need to periodically check water level controls and the
waterside of the pressure vessel cannot be overemphasized.
Most instances of major boiler damage are the result of
operating with low water or the use of untreated (or
incorrectly treated) water.
Always be sure of the boiler water level. The water column
should be blown down routinely. Check samples of boiler
water and condensate in accordance with procedures
recommended by your water consultant. Refer to sections E
and I in Chapter 3 for blowdown instructions and internal
inspection procedures.
A typical water level control is mounted in the water column
and has float actuated mercury switches. One switch is
connected to the burner limit circuit and will stop the burner
if a low water condition occurs. The other switch is connected
to the feedwater circuit to energize a water pump or feeder
valve to maintain water at the proper operating level.
Usually, the control is of the automatic reset type and will
remake the limit circuit when the water level is restored.
Some applications require that a control be equipped with a
manual reset mechanism that must be manually reset before
the burner can be restarted. This is usually accomplished with
the use of a second or auxiliary control that has this feature.
Since low water cutoff devices are generally set by the
original manufacturer, no attempt should be made to adjust
these controls to alter the point of low water cutoff or point of
pump cut-in or cut-out. If a low water device should become
erratic in operation or if its setting changes from previous
established levels, check for reasons and correct: Repair or
replace as required.
These controls normally function for long periods of time,
which may lead to laxity in testing on the assumption that
normal operation will continue indefinitely.
The controls' operation may be checked by stopping the water
supply to the boiler while the burner is operating at low fire.
While under constant attendance, allow the water level to
drop at a normal rate. Check for proper operation of the
feedwater controller and the low water cutoffs.
750-177
! DANGER
If a control does not break the circuit to stop
the burner at the proper point then shut
down the burner immediately. Failure to do
so may result in damage to the equipment.
Do not restart until all cross-connecting piping is checked for
obstructions. Also check the float bowl. If these are clean,
repair or replace the control. Repeat the above test to ensure
proper operation prior to returning the boiler to service.
On a steam boiler, the head mechanism of the low water
cutoff device(s) should be removed from the bowl at least
once a month to check and clean the float ball, the internal
moving parts, and the bowl or water column.
Remove the pipe plugs from the tees or crosses and make
certain the cross- connecting piping is clean and free of
obstructions. Controls must be mounted in a plumb position
for proper performance. Determine that piping is vertically
aligned after shipment and installation and throughout the life
of the equipment.
A scheduled blowdown of the water controls on a steam
boiler should be maintained.
Water Gauge Glass
A broken or discolored glass must be replaced at once.
Periodic replacement should be a part of the maintenance
program. Always use new gaskets when replacing a glass.
Use a proper size rubber packing. Do not use "loose packing,"
which could be forced below the glass and possibly plug the
valve opening.
Close the valves when replacing the glass. Slip a packing nut,
a packing washer, and packing ring onto each end of the glass.
Insert one end of the glass into the upper gauge valve body far
enough to allow the lower end to be dropped into the lower
body. Slide the packing nuts onto each valve and tighten.
If the glass is replaced while the boiler is in service, open the
blowdown and slowly bring the glass to operating
temperature by cracking the gauge valves slightly. After glass
is warmed up, close the blowdown valve and open the gauge
valves completely.
Check trycocks and gauge cocks for freedom of operation and
clean as required.
It is imperative that the gauge cocks are mounted in exact
alignment. If they are not, the glass will be strained and may
fail prematurely.
A blowdown cock is provided on the lower gauge glass fitting
and a daily blowdown is recommended.
Chapter 7
CAUTION
7-5