How is bleed air taken from a twin spool axial flow gas turbine engine compressor at high and low engine speed

Question

How is bleed air taken from a twin spool axial flow gas turbine engine compressor at high and low engine speed

Answer 1

Bleed air is taken from two bleed ports say the engine is CFM56B1 for B737-300, there is low stage bleed port on the 9th compressor stage and a high stage on the 14th stage compressor. during low speed or throttle lever at idle the engine bleed from the low stage is not enough to supply the users so high stage valve opens up the 14th stage to supply the aircraft user's need. The high pressure will push the low stage (9th) valve to close. At cruise or high power setting the bleed coming from the low stage (9th) is enough to supply the aircraft users so the High stage valve will stay close the 14th stage bleed port.

Answer 2

From CFM 56 engines the bleed air valve is located at the 9th & 13th stage of compression.

Some engines like the JT-8 will take air from from the 5th as well.