71.當加速到較高的壓力比P4／P1時，油門控制孔增大。減小了的壓力允許壓力比控制膜盒收縮，因
Fuel system

increases and the capsule moves the metering altitude is increased. This maintains the thrust 72．飛機高度的變化要求燃油流量發生變化，以滿足發動機推力和飛機爬升的要求。正常情況下，高度增加會降低壓力P1和P4，因此會打開壓力比控制活門并使燃油流量調節器膜盒膨脹，以減小可調節流孔的面積，進而減少供油。但是，為了滿足發動機推力和飛機爬升的要求，需要隨著高度的增加增大P4／P1。這個功能是由微調活門和一個感受壓力P1的膜盒來實現。當壓力P1減小時，微調活門移過P1控制孔，以減小控制壓力。該壓力由控制膜盒感測，靠作用在壓力比控制活門上的壓力，控制膜盒能隨著高度的增加延緩可調節流孔的關閉過程。這樣在保持油門處于固定位置的情況下，滿足了推力的要求。
sleeve to increase the V.M.O. area. The effect of requirement with the throttle at a fixed position.
opening the V.M.O. is to reduce the pressure difference and this is sensed by the pressure drop governor, which opens the pressure drop control orifice. The reduced system pressure difference is immediately sensed by the pressure drop spill valve, which moves towards the closed position and conse-quently increases the fuel output. The increased fuel flow accelerates the engine with a subsequent increase in pressure ratio (P4/P1). When the required pressure ratio is reached, the pressure ratio control valve opens and the F.F.R. capsule chamber pressure reduces. The capsule assembly expands, moving the V.M.O. sleeve to reduce the orifice area. The resultant increased pressure difference is sensed by the pressure drop control governor, which adjusts the pressure drop control orifice to a point at which the pressure drop spill valve gives a fuel output consistent with steady running requirements.
70.
During a rapid acceleration, the degree of overselling is mechanically controlled by the acceler-ation stop, which limits the movement of the pressure ratio control valve. A similar stop prevents the fuel supply from being completely cut off during a rapid deceleration.

71.
When accelerating to a higher P4/P1 ratio, the throttle control orifice is increased. The reduced pressure allows the pressure ratio control capsule to contract so that the valve contacts the acceleration stop. F.F.R. capsule chamber pressure increases and the capsule moves to increase the V.M.O. area. This action continues until the required P4/P1 ratio is reached. The increased P4 pressure allows the pressure ratio control capsule to re-expand and the valve to return to the steady running position.

72.
A change in altitude of the aircraft requires a variation in fuel flow to match the engine thrust and aircraft climb requirement. The normal effect of an altitude increase is to decrease the P1 and P4 pressures, thus opening the pressure ratio control valve and allowing the F.F.R. capsule to expand to reduce the V.M.O. area and, in consequence, the fuel flow. However, to match the engine thrust and aircraft climb requirement it is necessary to increase the P4/P1 ratio with increasing altitude. This is done by a trimmer valve and a capsule that is subjected to P1 pressure. As P1 pressure decreases, the trimmer valve moves across the P1 controlled orifice to reduce the control pressure. This is sensed by the control capsule, which, by acting on the pressure ratio control valve, slows the closure of the V.M.O. as

73.
To prevent the maximum L.P. compressor r.p.m. and engine gas temperature from being exceeded, a valve, known as the auxiliary throttling valve, is fitted in the outlet from the fuel pump, Under steady running conditions, the valve is held open by spring force, When limiting conditions are reached, the fuel flow is reduced in response to speed and temperature signals from the engine. The signals are amplified and passed to a rotary actuator that reduces the area of a variable restrictor. The effect of this is to increase the fuel pressure, which partially closes the throttling valve. H.P. fuel pressure acting on the face of the pressure drop spill valve is increased and the spill valve opens to reduce the fuel flow to the spray nozzles.

74.
H.P. shaft speed is also governed by the auxiliary throttling valve. Should other controlling devices fail and pump speed increases, the fuel pressure closes the throttling valve and opens the pressure drop spill valve to reduce the fuel flow.

75.
With the throttle closed, idling condition is determined by controlling the amount of air being vented through the idling adjuster and the ground idling solenoid valve, With both bleeds in operation, satisfactory flight idling for the air off-takes is ensured. By closing the solenoid valve a lower power condition for ground idling is obtained.

76.
This fuel system, like the combined acceleration and speed control system, has no pressurizing valve to divide the flow from the fuel pump into main and primary flows.
　
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