
Pratt & Whitney Rzeszów S.A.
MAINTENANCE MANUAL
PZL-10W ENGINE
1992.08.28
75-32-00
Page 3
Export Control Classification: PL/UE 9E999
2.
The signal from the electronic limiter unit to BV closing is supplied at
reduced N1 changing in
same range depending from the speed N1 increase. When the speed N1 increases fast
(acceleration) the closing speed is higher. When the speed N1 increases slowly (sweep) the
closing speed is lower.
B. The air bleed from beyond the compressor (CC BV).
Two bleed mushroom valve (see Dwg 3), symmetrical positioned on the combustion chamber case ensure the air bleed from
behind the compressor during . the engine starting.
The valve consists of the case (3), the mushroom head (1), the spring (2) and situating nut (4). The air pressure from behind
the compressor acts on the mushroom head on one side, while the spring resistance acts on second side. When the engine is
not running, the mushroom head ( 1 ) protrudes from the case (3) due to the spring (2) acting, and the valve is open. During
the first stage of the starting, the valve is still open and the air flows from the combustion chamber to the atmosphere trough the
ring gap and the openings is the valve case. At the next starting stage, after the air pressure behind compressor reaches the
value overcoming the spring (2) counteraction, the valve will be closed and remains at that state on all operating ratings up to
the engine shutdown, when is open again.
Earlier or later valve closing during the starting process depends on the spring (2) rigidity and has influence on the starting
quality at different ambient temperatures.
The valves with designations printed by an electrography on the front valve wall as follows may be installed on the engines:
(1)
19.31.0460
-
The valves which the spring force at closed valve arises 118 N ÷ 127 N (12 kG ÷ 13 kG,
26 lbs ÷ 29 lbs).
(2)
19.31.0370
-
The valves which the spring force at closed valve arises 176 N ÷ 196 N (18 kG ÷ 20 kG,
40 lbs ÷ 44 lbs).
Each from a/m valves may be used on the engine in whole range of the operation ambient temperatures.
At the extreme high or extreme low ambient temperatures may appear the causes of the engine starting difficulties.
At the extreme high ambient temperature may occur*the "hot suspension" (lack increase) of the compressor turbine rotational
speed during the starting. At that case at least one valve with the spring of high rigidity (designed as in subitem (2)) shall be
replaced for the valve with the spring of the low rigidity (designed as in subitem (1 )),