Fuel Vent System Component Location
Figure 1 (Sheet 5)
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3. Fuel Vent Float Valve (Fig. 2)
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A. The fuel vent float valves are located near the top of the tank to prevent fuel from entering the vent system during airplane attitude changes. The valve consists of a float mounted on an arm hinged at the mounting flange. The mounting base is installed over the vent port of the vent system tubing. A valve attached to the float arm contacts and closes the port if the float is contacted by rising fuel. The valve is held in the normally open position by the weight of the float and arm.
B. On increasing fuel levels, the valve will be fully closed when the fuel level reaches 0.20 inch below the valve seat. The valve will not open at less than 1.00 inch below the valve seat on decreasing fuel levels.
4. Fuel Vent Drain Valve (Fig. 2)
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A. The float actuated drain valves are located at low points in the vent tubing. The valves are normally open to drain condensate and fuel from vent system tubing. Each valve consists of a mounting flange, poppet assembly, float, and a shroud.
B. When fuel contacts the float, the poppet will close against a seat before fuel can enter the vent tube. The valve will open when the fuel level drops below the float level.
5. Surge Tank Drain Check Valve (Fig. 3)
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A. Surge tank drain check valves are installed on the end of each surge tank drain line. The valves are located at the tank end rib of each inboard main tank. The valve consists of a housing, with threads to attach to a coupling at the end of the surge tank drain line, and a spring-loaded flapper.
B. The surge tank drain check valve prevents reverse fuel flow from the inboard main tanks into their respective surge tanks. The flapper is normally spring-loaded to the closed position, but opens to allow fuel to drain from the surge tank.
6. Surge Tank Vent Flame Arrester (Fig. 4)
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A. Flame arresters are installed in the wing surge tank vent tubes, outboard of the surge tank. A flame arrester consists of a stainless steel honeycomb core surrounded by a mounting ring.
B. The flame arrester prevents any external flame from entering the surge tank. The honeycomb core acts as a heat sink, cooling the flame front below the ignition point of fuel vapor.
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FUEL VENT DRAIN VALVE
Fuel Vent Valves
Figure 2
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7. Fuel Vent Scoop (Fig. 1)
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A. Fuel vent scoops are located near the trailing edge of each wing tip. The wingtip vent scoops are connected to the wing surge tanks through the surge tank vent line.
B. The vent scoops apply a slight pressure head in flight to reduce fuel vaporization at altitude, and to provide positive pressure at the inlet ports of the fuel system pumps.
8. Surge Tank Pressure Relief Valve (Fig. 5)
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A. To protect wing structure against positive and negative overpressure, a pressure relief valve is installed on each wing surge tank access door.
B. The pressure relief valve is normally latched closed. When positive or negative pressure limits are exceeded, the valve opens. Once opened, the valve stays open until manually reset by pulling the T-handle.
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