transient bleed valve
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Joined: Oct 2008
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From: usa
transient bleed valve
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!
Thanks in advance!
Last edited by sama_RA; 3rd November 2009 at 17:28.
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From: USA
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.
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.
Joined: Aug 2007
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From: East England
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......
Joined: Mar 2009
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From: Middle East
Any possibility of the stuck closed valve causing compressor to stall as a result of insufficient pressure supply?
