yakbird
Joined: 17 Mar 2006
Posts: 2
Location: Warwickshire UK
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 Posted: Fri Mar 17, 2006 8:05 am Post subject: Yak-18T air regulation |
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On my '52 the air system pressure was crudely regulated. The compressor keeps on pumping till the system pressure overcame a 'blow-off valve' a simple affair with a spring-loaded piston pressing a rubber seal against a seat. A big puff of air, lot of noise (not normally heard in flight) and pressure dropped back until valve spring pressure reseated. Easy to adjust to ensure you always had sufficient pressure in the system.
On the 18T it is a bit more refined (apparently) with the pressure detection valve operating in a 'flip-flop' manner. When it reaches pre-set maximum system pressure the unit 'vents' the output from the compressor which now 'freewheels'. As the system pressure drops slowly (through small leakage) there comes a point when the valve 'switches' the compressor output back on line.
Problem is that the hysteresis and set points are too wide. Pressure builds up to about 55 kg/cm, valve triggers and system has to drop to around 25 kg/cm before it comes on line again.
Guess at which point in this cycle I tend to be landing, needing flaps, U/C and brakes??
Do any of you have any experience with this valve/sensor and its adjustment. Its safe to tell me, I am an engineer...honestly 
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