Installation
2-8
750-204
Profire D/LND
An oil circulating pump provides continuous oil circulation to the circulation loop. A back pressure valve holds
10 to 15 PSI on the loop system. With the oil supply line connected only to the oil metering pump inlet, all oil
must pass through the pump. During pre-purge, unmetered oil flows through a bypass section of the oil metering
pump. Metered oil passes through the metering section to a de-energized 3-way oil valve (common port). Both
unmetered and metered oil must pass through the back pressure valve and return to an oil storage tank. The oil
metering pump will only meter oil. It will not serve as a circulating pump. At trial for main flame (main fuel), the
3-way oil valve is energized admitting metered oil to the nozzle for atomization and fast smooth ignition. Unmet-
ered oil continues to flow through the bypass section of the oil metering pump and returns to an oil storage tank.
2.8 — Circulating Oil Pump
A circulating oil pump is required to deliver fuel oil from the storage tank to the burner at a minimum of 150% of
the maximum burner firing rate. The excess oil allows a margin for piping error, viscosity changes in the fuel oil,
and circulating pump wear. Correct pipe sizing is determined by circulating rate, not burner capacity. Install the
pump as close to the supply tanks as possible. Suction lift should be as low as possible. Maximum suction of
15” Hg vacuum is good practice for either light or heated heavy oil. The strainer should be installed in the suc-
tion line just ahead of the circulating pump to prevent foreign material from entering the pump. Locate the
strainer so it may be easily cleaned.
2.9 — Oil Loop Heater
This heater should heat the fuel oil for proper burning at full firing rate. The proper oil temperature is that which
gives the best results with the particular oil being fired. This may vary widely with different fuels in different firing
systems. Residual oil viscosity can vary widely within grade limits and is not always within the specified limits of
the grade. Fuel viscosity requirements for air atomizing burners are not critical. Under typical circumstances, a
viscosity of 100 SSU might be optimum, but good results may be obtained up to 150 SSU. There is no advan-
tage to less than 100 SSU.
Where the burning characteristics of the fuel are unknown, the following may be considered as typical:
2.10 — Burner Mounted Trim Heater
An auxiliary trim heater is in line between the metering pump and 3-way oil valve. The auxiliary trim heater is
used for topping off oil temperature prior delivery to the nozzle.
2.11 — Back Pressure Valve
A back pressure valve, similar to Watson McDaniel type “R,” needs to be installed on the return line as shown in
Figure 2-6. This valve must be installed in an upright vertical position. Before installing the valve, be sure to
No. 4 80º - 125º F
No. 5L 115º - 160º F
No. 5H 145º - 180º F
No. 6 180º - 220º F
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