Page 74 - Boiler_Operators_Handbook,_Second_Edition

Boiler Plant Operations 59

Figure 2-3. Manometer on slope

the square of flow so the measurement when you are at or a specific pressure for a modulating burner. Pressure
1/4 flow (25%) will be 1/16 of the reading at high fire. atomizing burners will follow the rules for flow and
Run your modulating controls down to the bottom to pressure drop but air and steam atomized burners don’t.
see if the manometer reading is about 1/16 of what you If you can’t get the information from the manual use the
got at high fire. If it isn’t check that manual again; some pressure that’s half the range of the pressure gauge for
boilers are only rated for a 2 to 1 turndown so low fire is fixed fire burners, 1/5 of that for modulating pressure
50% and the differential pressure reading would be 1/4 atomizing burners, and 1/16 of it for steam or air atom-
of the high fire value. ized burners. Half the gauge is explained in the chapter
If you must adjust linkage, and that’s very pos- on measurements.
sible, remember to check for any changes to the high fire Once you’ve established the required oil pressure
reading after you’ve ensured the controls will stroke (go for light-off you can set it. Close the fuel oil recirculation
from high to low and back) without binding any of the control valve; a globe type valve in the fuel oil return
linkage. Once you’ve established light-off combustion line at the boiler. Position the controls at low fire on
air flow you can set up the fuel or fuels. modulating boilers. That can be as simple as holding the
Setting up fuel oil at low fire should be a snap. “decrease” push-button on a jackshaft controlled boiler
The only problems with it could be an improper piping to several adjustments on a pneumatic control valve.
design which, among other things, doesn’t include any Slowly open the fuel oil supply valve while observing
fuel oil return. As far as I’m concerned if you install a the burner supply pressure gauge. Slowly is because
boiler without a fuel oil return line you’re setting it up you could interrupt the flow of oil to another (operat-
for a furnace explosion! With a fuel oil return line you ing) boiler and shut down the plant. (That’s said by a
can set up your oil conditions without creating a fire. dummy that did it more than once!) The burner pressure
Before opening the oil valves, make sure the oil should suddenly jump to oil supply pressure because
atomizer is not in the burner or open a joint at the hose the recirculating valve is closed and there is no flow
or tubing to the burner so you know you’re not dump- through the piping.
ing oil during this process. Who says the safety shut-off Now you know why we want to be sure no oil
valves don’t leak? is going to the atomizer, if the safety shut-off valve is
Once again check the instruction manual, this time leaking there will be oil dripping or spraying out of
you’re looking for a burner oil pressure at light-off. the burner yoke or the opening we created. Needless
That’s either operating pressure for a fixed fire burner to say, if the safety shut-off leaks we stop start-up and