2.9.
PRESSURIZING AND DRAIN DUMP VALVES
Until sufficient pressure is attained in the fuel control to
compute the fuel flow schedules, flow to the main fuel nozzle is
prevented by the pressurizing and drain dump valve. This valve also
drains the fuel manifold at engine shutdown to prevent postshutdown
fires, and it traps fuel in the upstream portion of the system to
keep the fuel control primed to permit faster starts.
All manufacturers install a combustion chamber drain valve in
the combustion section. During normal engine operation this valve is
closed. The drain valve is located at the lowest part of the
combustion chamber. When the combustion pressure in the chamber
drops below a specified minimum, usually a few pounds per square
inch, this valve opens and drains any fuel remaining after a false or
aborted start. The fuel drained from this valve is dumped overboard.
2.10.
FUEL OILCOOLER
Some turbine engines use a fuel oilcooler or heat exchanger
to cool the lubricating oil. This unit is discussed under the
lubrication system because its prime function is to help cool the
oil. It consists of a cylindrical oil chamber surrounded by a jacket
through which the fuel passes. Heat from the oil is transferred to
the fuel via conduction*. Figure 2.11 shows a typical fuel oil
cooler.
Figure 2.11. Fuel OilCooler.
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*See glossary.
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