Cleaver-Brooks CBH 40 - Air Damper Adjustment; Safety Valves

Chapter 5-Adjustment and Maintenance
the intermediate (HFOV-1) and the high fire
(HFOV-2) oil valves.
The variables involved preclude specifying the
position of the cams by degree of angle since their
point of actuation is directly related to the amount
of damper travel on a particular burner. Damper
movement may be set to a greater or lesser amount
of opening depending upon job conditions and
combustion needs. Cam position can best be ex-
plained by detailing the function of the switch it
actuates.
The first switch (AS-1) is actuated to close mid-
way between low and high fire. This causes the in-
termediate oil valve to open and the second nozzle
to fire, providing an increased firing rate for a
smoother change-over between the low and the
high fire rates and vice versa. As it moves towards
the high fire, the air damper allows an increasing
amount of air into the boiler. The valve should
open at approximately mid-range, but definitely at
a point when sufficient air is present so that there
is no incomplete combustion or smoke caused by
an improper air/fuel ratio. The positioning of the
cam must be guided by observing the fire or stack
when the valve opens. If smoke or haze is noticed,
reposition cam to slightly retard valve opening.
The second oil valve switch (AS-2) should be ac-
tuated just as damper reaches its open position. On
the basis of a combustion analysis, damper
position or linkage adjustment may be required to
provide more or less air at this point.
In the event of a component replacement, note
position of cams and replace them as near· as
possible to their original position; but be sure to
check for proper switch actuation. If a switch is
replaced, make sure that wiring connections are
correct. The set screw holding the cam should be
checked occasionally for tightness.
I. AIR DAMPER ADJUSTMENT
Since the rate at which fuel is delivered is adjust-
able only within narrow limits, setting of the air
damper is the primary means of obtaining the
correct ratio of fuel to air to insure the most ef-
ficient combustion. The arms and connecting rod
that transmit motion from the damper motor to
the air damper (and to the gas butterfly valve on a
gas-fired unit) are set at the factory and should not
normally need further adjustment. If adjustments
are required, proceed as follows:
Normally, at low fire the damper is cracked
slightly open. A stop screw limits the amount of
travel. With the burner firing at low rate, back off
the screw to allow the damper to further close until
a slight haze appears in the stack. Gradually open
the damper until the haze disappears. Lock the ad-
justment screw in this position.
Turn the damper positioning switch to high fire.
5-18
Turn the high fire adjustment screw to slightly
close the air damper until a slight haze appears.
Re-adjust the screw to open the damper to a posi-
tion where the haze disappears. Lock the adjust-
ment screw in this position.
Consider these settings to be only approximately
correct. Final adjustment should be made using a
flue gas analyzer.
Adjust the linkage and the arms so that a smooth
damper movement occurs. Observe the burner as it
cycles to high fire and back to low to be sure that
the air flow is coordinated with the fuel flow. Too
much air may extinguish the flame while an in-
sufficient amount will cause a smokey changeover.
The following factors can serve as guides in
linkage adjustment:
(a) The damper motor must be able to complete
its full travel range of 75 degrees. A re-
striction can cause damage.
(b) The closer the swivel joint in the motor arm
is to the hub, the less distance it will travel.
(c) The amount of damper opening increases
when its connecting joint is closer to the hub.
To decrease opening move the ball joint
away from the hub.
(d) Final adjustments should result in a coor-
dinated movement of the damper and dam-
per motor.
(e) Over-travel linkage should not be required to
extend its spring to fullest stretch.
Periodically check for proper adjustment. Check
tightness of setscrews to prevent slippage. Oc-
casionally oil swivel joints with a graphite or sili-
cone type lubricant.
J. SAFETY VAlVES
The safety valve is a very important safety device
and deserves attention accordingly.
The purpose of the valve(s) is to prevent pressure
build up over the design pressure of the pressure
vessel. The size, rating and number of valves on a
boiler is determined by the ASME Boiler Code.
The installation of a valve is of primary im-
portance to its service life. A valve must be moun-
ted in a vertical position so that discharge piping
and Code required drains can be properly piped to
prevent build up of back pressure and accumu-
lation of foreign material around the valve seat
area. Apply only a moderate amount of pipe com-
pound to male threads and avoid overtightening as
this can distort the seats. Use only flat jawed wren-
ches on the flats provided. When installing a
flange connected valve, use a new gasket and draw
the mounting bolts down evenly. Do not install or
remove side outlet valves by using a pipe or
wrench in the outlet.
A drip pan elbow or a flexible connection between