PART 1-DESCRIPTIVE
3. Main fuel feed
(a) Low pressure
The L.P. pumps at the base of each compartment of the
main tank deliver fuel via the L.P. cocks to the H.P.
pumps. Should an L.P. pump fail, fuel will by-pass the
pump and be fed to the H.P. pump by gravity, via non-
return valves.
(b) High pressure
From the H.P. pump, fuel flows at high pressure to the
throttle valve and the barometric pressure control (B.P.C.).
The B.P.C. maintains the correct fuel-air ratio for all alti-
tudes, speeds and throttle settings. From the throttle valve,
fuel passes through the H.P. cocks and then through
pressurising valves to the main and pilot burner lines and
thence to the duple burners. When pressure is low (i.e. at
low r.p.m.), the pressurising valve feeds fuel to the burners
through the pilot line only and, when pressure rises,
through both the main and pilot lines.
(c) Starting and relighting fuel supply (Derwent Mk.8 only)
On the Derwent Mk. 8 engine, fuel for starting and
relighting is drawn from the main line between the L.P.
cock and the H.P. pump and passes to the torch igniter via
a priming pump, which is automatically operated when
either the starting or the relight button is pressed.
4. Fuel controls
(a) L.P. pumps circuit breakers
The circuit breakers (19) for the port and starboard pumps
are at the forward end of the port shelf in the front cockpit.
These circuit breakers must be made to complete the
engine-starting circuit and should remain made at all times
when the engine is running. Test pushbuttons (24) and an
ammeter socket (21) are provided for testing the pump
output.
(b) L.P. cock levers
The L.P. cock levers are at the rear of each cockpit, one on
either side of the seat. In the front cockpit the levers (1,80)
are the inner ones of the pair on each side of the seat; in
the rear cockpit the levers (87, 124) are the rear ones of11
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