Technical data

13773-001
28-20
Page 1
DISTRIBUTION
1. DESCRIPTION
This section contains information on the distribution system. The fuel distribution system consists of elec-
tric and mechanical (engine-driven) fuel pumps, fuel gascolator, fuel hose, fuel lines, fuel selector valve,
and the fuel pump switch.
A gascolator is installed on the forward side of the firewall after the electric fuel pump and before the
engine driven fuel pump. A drain valve, connected to the bowl of the gascolator, is used to drain off con-
taminates during the preflight inspection. The gascolator provides 100 to 140 micron filtration and has a
4.9 fluid ounce (144.89 milliliters) capacity. The filter element can be cleaned or replaced when the bowl is
removed.
Note: The majority of all fuel system problems are directly related to contaminated fuel. Therefore
inspecting and cleaning the fuel drains and filter in the gascolator should be considered to
be of utmost importance. Under normal operating conditions the fuel drains and filter in the
gascolator should be inspected and cleaned as called out in Chapter 5. If the airplane is
used in dusty or dirty environments, the fuel drains and filter in the gascolator should be
cleaned more often.
The engine-driven fuel pump is mounted to the aft side of the engine. An electric fuel (boost) pump is
installed on the forward side of the firewall. Mounted on the center console (adjacent to the fuel selector
valve) is a Fuel Pump BOOST-PRIME rocker switch. The prime position on the switch is momentary. The
boost position is continuous. For engine starting, pressing PRIME causes the boost pump to operate at
high speed until the fuel pressure reaches 2-4 psi. When the fuel pressure reaches the 2-4 psi range a
pressure switch in the fuel injection line switches the boost pump to the low-speed mode to provide a 4-6
psi fuel pressure boost. Two-speed prime allows the fuel pressure to rapidly achieve proper starting pres-
sure. Once the fuel system is primed, the electric pump is switched to the low setting by the pressure
switch. Selecting BOOST energizes the boost pump in low-speed mode to deliver a continuous 4-6 psi
boost to the fuel flow for vapor suppression in a hot fuel condition. The boost pump operates on 28 VDC
supplied through the 7.5-amp FUEL PUMP circuit breaker on Main Bus 1. The boost position operates the
electric pump on the low-speed setting only, regardless of the fuel system pressure.
A fuel tank selector valve is installed in the center console between the crew seats, and is isolated from the
cabin in case of leakage. The valve has a left, right, and off position. Each position has a positive detent. A
knob is located at the top of the handle, and must be pulled to switch the valve to the off position; the valve
can be rotated back to on without any further action. The selector valve can be switched between left and
right fuel tanks by simply rotating the valve. The valve handle points in the direction of the tank being
selected. The selector valve only allows feed from one tank at a time.
Drain hoses are provided for the auxiliary fuel pump, gascolator, engine driven fuel pump, fuel injection
manifold (spider), and the engine manifolds (cylinder heads). Drain hoses are routed to a drain manifold
located on the bottom center of the firewall. A check valve is installed on the cylinder drain manifold to pre-
vent loss of manifold pressure. The valve closes when manifold pressure is below ambient pressure. An aft
side firewall fuel enclosure, and a selector valve enclosure prevent fuel from leaking into the cabin. If fuel is
leaking from either enclosure, the component causing the fuel leak must be repaired immediately to pre-
vent fuel from entering the cabin.
Note: When servicing fuel system pipe thread fittings, apply a small amount of grease (MIL-G-
60320 Type 1) to the external threads.
30 Nov 2000