View Full Version : transient bleed valve
sama_RA
3rd Nov 2009, 15:40
On CFM56-5B/7B engines, how it would affect engine performance if the high stage bleed air valve (9th stage) is irresponsive (stuck closed, or open) provided the 5th stage bleed supply is adequate.
Thanks in advance!
muduckace
3rd Nov 2009, 15:56
Not a ton of cfm56 experience but I believe it is set up similar to a GE or Pratt as opposed to RR.
Stuck open could generate over pressure over temp bleed, 5th stage should still regulate it but there is usually a secondary valve to isolate the engine from the manifold if stuck wide open after giving a high press/temp bleed indication.
Stuck closed you would have little air at ground idle and slightly more at flight idle. Often these stuck closed discrepancies are found at top of descent as the engine transitions from cruise to flt idle (bleed air off/low etc.).
As far as engine performance stuck closed no issue, stuck open a slight decrease in thrust/efficiency unless a secondary protection S/O valve isolates the engine then no issue just less bleed air to operate packs/trim air etc..
Like I said this is general systems knowledge, someone with more time on this engine and the wing it hangs off (737/A340/Dc-8?) of may validate or negate some of the details of my post.
spannersatKL
3rd Nov 2009, 16:14
If high stage valve (or what ever each manufacturer calls it) is stuck open at high thrust it will cause relief valve to open and dump surplus air, also pressure regulating / shut off valve will move to close due to over heat of the air flow. If stuck closed then as stated by mudukace then no real effect except on the ground at idle......pack flow low etc. and of course at top of descent when lack of flow / pressure will show as possible difficulty in maintaining cabin altitude and on some types as you continue descent possible lack of thermal anti icing......
sama_RA
3rd Nov 2009, 17:27
Thank you! This helps a lot.
Any possibility of the stuck closed valve causing compressor to stall as a result of insufficient pressure supply?
Any possibility of the stuck closed valve causing compressor to stall as a result of insufficient pressure supply?
Normally not. The HP Bleed VLV is normally closed during cruise and only opening at low power, when pressure and flow from 5th stage is not sufficient.
spannersatcx
4th Nov 2009, 16:58
Any possibility of the stuck closed valve causing compressor to stall as a result of insufficient pressure supply?
As you can dispatch with HP valves locked closed, then no.