FM 1-506 Fundamentals of Aircraft Power Plants ... - Survival Books

WWW.SURVIVALEBOOKS.COMFM 1-506the manifold. The flow divider allows fuel to flow to theprimary and secondary manifolds depending on fuelpressure. (See Figure 4-3.)Pressure-Operated Valve. Some manufacturers,such as Allison and Lycoming, install a pressureoperatedvalve in the combustion chamber section.When the pressure in the burners drops below a specifiedminimum, usually a few pounds per square inch, this valvewill open and drain any residual fuel remaining after afalse start or normal shutdown. (Refer to Figure 4-4 tosee where this drain valve fits into the system.)Fuel HeaterGas turbine engine fuel systems are very susceptible tothe formation of ice in the fuel filters. When the fuel in theaircraft fuel tanks cools to 32°F or below, residual water mthe fuel tends to freeze when it contacts the filter screen.A fuel heater operates as a heat exchanger to warmthe fuel. The heater can use engine bleed air, an air-toliquidexchanger, or an engine lubricating oil, a liquid-toliquidexchanger, as a source of heat.4-4