PART 1-DESCRIPTIVE
(c) After a period of 30-40 seconds the time switch cuts
off the starting circuit and the engine accelerates under
its own power to idling r.p.m. 3,000±200.
12. Engine relighting system
A pushbutton (4) is incorporated in the end of the H.P.
cock lever. It should be pressed to energise the igniter
plugs when relighting in flight. It may also be used as
an audible check that the H.E. ignition is functioning.
The relight system will operate irrespective of the engine
starter master switch.
13. H.P. pump isolating valve
(a) The output of the H.P. pump is monitored by the B.P.C.
through the pump servo system. A solenoid-operated
isolating valve is fitted to enable the pump to be isolated
from the servo system. When the FUEL PUMP
ISOLATING SWITCH (48) adjacent to the booster
pump switch is on, the valve isolates the H.P. pump from
the servo system and the pump then moves to full stroke
and is controlled by the pump overspeed governor
and by the throttle position.
(b) The isolating valve is primarily intended as a means of
restoring power in flight if failure of the servo system
causes a sudden drop in engine r.p.m. It may also be
used as a safeguard against failure of the system during
take-off, if desired. It must be switched OFF as soon as
a safe height is reached, otherwise overfuelling will occur,
resulting in rising j.p.t. and increasing r.p.m. as height
is gained.
NOTE:-If failure of the servo system occurs whilst
isolated there is a probability of fuel starvation
leading to flame-out when the switch is returned
to OFF.
14. Engine fire-extinguisher
(a) The combined fire-extinguisher pushbutton (29) and
engine FIRE warning light is on the right of the upper
panel above the flap position indicator. When Mod.
3471 is incorporated a second red light (28) is positioned
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