The variable bleed valves on a engine at start up is
- open
- closed
- modulating
Explanation from PART66Online
Variable bleed valves are held open during start and at low power to spill surplus compressor air, preventing the front stages from stalling or surging while the compressor is unmatched. As the engine accelerates to higher speeds the valves close. They are therefore open, not closed or modulating, at start-up.
S
sasna asked · 16 Aug 2013
bleed valve of the engine remain open during the starting of the engine???????????????????
Community Comments (4)
P
PART66Online
17 Aug 2013
Hello.
Bleed valve are fitted to extend the range of smooth operation over lower engine speeds. In the lower speed range the bleed valve opens to allow some of the air to escape from the rear stages of the compressor, thus restricting the mass air flow through the later stages and preventing an unstable flow pattern. I think you are confused with bleed valves what are used for air conditioning and so on... :)
Bleed valve are fitted to extend the range of smooth operation over lower engine speeds. In the lower speed range the bleed valve opens to allow some of the air to escape from the rear stages of the compressor, thus restricting the mass air flow through the later stages and preventing an unstable flow pattern. I think you are confused with bleed valves what are used for air conditioning and so on... :)
S
sasna
17 Aug 2013
ok.... you are referring to VBV.
P
PART66Online
17 Aug 2013
Uhu, question is about VBV, I'll correct this question to avoid misunderstandings in future. :)
A
ademceven
19 Feb 2020
yes its open in order to enable more easy startup, if you close vbvs it would be far too hard to crank the engine since pressure feedback would force compressors to slow
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