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B737 electric hydraulic pumps ..... B737 electric hydraulic pumps .....
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Old 08-19-2008, 11:31 AM   #1 (permalink)
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Default B737 electric hydraulic pumps .....
-can someone clarify if the electric hydraulic pumps are turned on or off prior to engine start? Also does anyone have an actual checklist? (this question applies to the Next Generation series.)
Last edited by Brent H : 08-19-2008 at 11:49 AM.
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Old 08-19-2008, 02:24 PM   #2 (permalink)
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It differs by airline. I've been out of the Boeing for a time but I believe we have all pumps on for start at Alaska. This is controversial to some because leaving the A pumps on pressurizes the nose wheel steering during push. Our ground crews must install a by-pass pin to open a by-pass valve so the NWS is not active during push.

You may like this site. http://www.b737.org.uk/ It is full of technical data/diagrams/tests for your reading pleasure.
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Old 08-19-2008, 08:00 PM   #3 (permalink)
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If I remember right the pumps on the 737NG aircraft are turned on at the gate before pushback and left on for the remainder of flight. I'm not aware of any reason to turn them off during engine start.
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Old 08-19-2008, 08:06 PM   #4 (permalink)
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Quote:
Originally Posted by mike734 View Post
It differs by airline. I've been out of the Boeing for a time but I believe we have all pumps on for start at Alaska. This is controversial to some because leaving the A pumps on pressurizes the nose wheel steering during push. Our ground crews must install a by-pass pin to open a by-pass valve so the NWS is not active during push.

You may like this site. The Boeing 737 Technical Site It is full of technical data/diagrams/tests for your reading pleasure.

Mike is right, A pumps pressurize NWS. We turn A (Engine Driven) off for push-back. But other airlines have they're own ops. Hope this helps
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Old 08-20-2008, 01:31 PM   #5 (permalink)
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As long as the NWS lock-out pin is installed, we turn on both Elec pumps prior to push (good time to find if you have a system leak & it will bring up the LEDs if they are drooping). Eng pumps are never turned off (allowing for thermal expansion after shutdown).
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Old 08-21-2008, 06:39 PM   #6 (permalink)
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I know in the 757/767 there is a procedure called Hard Starting which is used at hot and high altitude airports (Bogota comes to mind). In essence you turn off the Eng Driven pumps and Generators to allow the engines to spool up faster. Once you are stabilized at idle you turn them on.
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Old 08-22-2008, 12:02 AM   #7 (permalink)
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We turn off our A pumps for push as well. I thought we were the only ones.
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Old 08-27-2008, 07:37 PM   #8 (permalink)
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Errr...
SGRogue...the engine driven pumps are left ON all the time because that allows the hydraulic pump shutoff solenoid to remain de-energized, and thus doesn't burn out!

DAL4EVER...tell me, how does turning off the generator switches unload the engine during spool-up?

Cheers...E...
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Old 08-28-2008, 12:51 PM   #9 (permalink)
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my bad...different airplane with the Eng Driven pumps left on for thermal expansion. Bulfer does have it listed for the exact reason you stated.
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Old 09-01-2008, 04:57 PM   #10 (permalink)
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Errr...
SGRogue...the engine driven pumps are left ON all the time because that allows the hydraulic pump shutoff solenoid to remain de-energized, and thus doesn't burn out!

DAL4EVER...tell me, how does turning off the generator switches unload the engine during spool-up?

Cheers...E...
Not sure, but that's the description in the supplemental section regarding engine starts when it references Hard Starting. It made me think about it as well as you are not physically disconnecting the generator drive shaft from anything. But that's the description so I thought I'd volunteer it.
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