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HAWK21M
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Steering Bypass Valve B737 Reliability.

Tue Mar 22, 2011 10:36 am

How Reliable are the Steering Disconnect valve [near the NLG] for the B737s out of experience.
How is it on the later B732s that had them installed.
Heard they were unreliable & caused Hyd pr to leak past hence Pushback & startup was an option discontinued on the B732s.
regds
MEL.
I may not win often, but I damn well never lose!!! ;)
 
AA737-823
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RE: Steering Bypass Valve B737 Reliability.

Thu Mar 24, 2011 9:48 pm

Quoting HAWK21M (Thread starter):
How Reliable are the Steering Disconnect valve [near the NLG] for the B737s out of experience.
How is it on the later B732s that had them installed.
Heard they were unreliable & caused Hyd pr to leak past hence Pushback & startup was an option discontinued on the B732s.

I've never experienced any problem of the ones you've listed. Lots of things leak on 737-200s; the steering bypass valve is one thing that I have NEVER seen leak, either internally or externally.

I do know that the design changed COMPLETELY from the classic to the NG; perhaps this is related to the information you've come across.

But I've never even had to touch one, except during nose gear work.

The parking brake valve, on the other hand............
 
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HAWK21M
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RE: Steering Bypass Valve B737 Reliability.

Fri Mar 25, 2011 10:29 pm

Quoting AA737-823 (Reply 1):
Lots of things leak on 737-200s; the steering bypass valve is one thing that I have NEVER seen leak, either internally or externally.

The reason I heard was since the Steering Disconnect valve was unreliable & leaked System A Pressure to the gears it was not advisable to run the Engines during pushback.
regds
MEL.
I may not win often, but I damn well never lose!!! ;)
 
AA737-823
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RE: Steering Bypass Valve B737 Reliability.

Tue Mar 29, 2011 11:32 pm

Quoting HAWK21M (Reply 2):
The reason I heard was since the Steering Disconnect valve was unreliable & leaked System A Pressure to the gears it was not advisable to run the Engines during pushback.
regds

Wow, well, I've never come across that, either in published paper or in tribal knowledge....
It's interesting, though... Maybe I'll ask around and see if any of the old-timers have any such experience!
 
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CALTECH
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RE: Steering Bypass Valve B737 Reliability.

Wed Apr 06, 2011 2:42 am

Quoting HAWK21M (Thread starter):
Heard they were unreliable & caused Hyd pr to leak past hence Pushback & startup was an option discontinued on the B732s.

Not unreliable. The thing on the old 737-200s was that the engine pumps provided 'A' system pressure, the electric pumps provided 'B' system pressure. Same thing on the 727s which only two of their engines had hydraulic pumps, and the 727s had a gizmo called a 'ground interconnect' for the hydraulics, nasty trouble if one wasn't careful.

Back to the 737-200. You push back and the 'B' system electric pumps were running, which supplied brake pressure if I remember correctly. Then the flightdeck starts up a engine or both, which gave one 'A' system press. 'A' system pressure provided nose wheel steering. Now, the pushback crew wasn't careful and did not line up the towbar exactly straight when disconnecting the tug from the towbar, the poor person who went and pulled out the steering bypass valve pin, now had the towbar swing towards neutral and take your lower legs out.

The flightdeck never really shut the engine driven pumps to off, for the pump shutoff solenoids were powered to off and would burn up after a while. So the engine driven pump switches were always on. A bit dangerous if one wasn't careful.

Quoting AA737-823 (Reply 1):
I've never experienced any problem of the ones you've listed. Lots of things leak on 737-200s; the steering bypass valve is one thing that I have NEVER seen leak, either internally or externally.

I do know that the design changed COMPLETELY from the classic to the NG; perhaps this is related to the information you've come across.

But I've never even had to touch one, except during nose gear work.

The parking brake valve, on the other hand............

The design changed with the 737-300/-500, which is also on the 737 NGs. One 'A' system engine driven and one 'A' system electrical pump, same for 'B' system.

Quoting HAWK21M (Reply 2):
The reason I heard was since the Steering Disconnect valve was unreliable & leaked System A Pressure to the gears it was not advisable to run the Engines during pushback.

To be extra safe, it is advisable to disconnect completely from the aircraft before engine start. The unreliability was people forgetting how the system worked. Same here, never heard of the Steering Disconnect valve leaking. Have seen and heard of people using bypass pins that were too small, and memory serves, this too would allow pressure to still flow to the steering.

Quoting AA737-823 (Reply 3):
Wow, well, I've never come across that, either in published paper or in tribal knowledge....
It's interesting, though... Maybe I'll ask around and see if any of the old-timers have any such experience!

Old-timers, damn, didn't think I was that old.
UNITED Would Be Nice
 
AA737-823
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RE: Steering Bypass Valve B737 Reliability.

Thu Apr 07, 2011 11:13 am

Quoting CALTECH (Reply 4):
The design changed with the 737-300/-500, which is also on the 737 NGs. One 'A' system engine driven and one 'A' system electrical pump, same for 'B' system.

I was referring to the bypass valve itself; I'm a mechanic for -200s and -NG's, but haven't worked the -3/4/5.
So are you telling me that the BYPASS VALVE itself changed on the -300? Or just the layout of the hydraulic system? I'm familiar with those changes, ad nauseam! Thank you, Alteon Gen-Fam...

Quoting CALTECH (Reply 4):
Old-timers, damn, didn't think I was that old.

Hah, well.... if you've been around LOTS of -200s, I'm gonna say you're at least... seasoned.
 
 
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CALTECH
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RE: Steering Bypass Valve B737 Reliability.

Thu Apr 07, 2011 3:19 pm

Quoting AA737-823 (Reply 5):
I was referring to the bypass valve itself; I'm a mechanic for -200s and -NG's, but haven't worked the -3/4/5.
So are you telling me that the BYPASS VALVE itself changed on the -300? Or just the layout of the hydraulic system? I'm familiar with those changes, ad nauseam! Thank you, Alteon Gen-Fam...

The -100/-200 days were so long ago but I do think the bypass valve itself was changed, but the layout of the hydraulic system changed completely. -100/-200 engine pumps ran 'A' System, electric pumps ran 'B' Sytem.

-100/-200

-300 and onwards
UNITED Would Be Nice
 
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CALTECH
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RE: Steering Bypass Valve B737 Reliability.

Thu Apr 07, 2011 5:14 pm

Quoting AA737-823 (Reply 5):
Hah, well.... if you've been around LOTS of -200s, I'm gonna say you're at least... seasoned.

Sssshhhhh, even worked on 737-100s. With aircraft airstairs FWD and AFT installed. Those were dinosaurs.
UNITED Would Be Nice
 
AA737-823
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RE: Steering Bypass Valve B737 Reliability.

Fri Apr 08, 2011 11:05 am

Quoting CALTECH (Reply 6):
-100/-200 engine pumps ran 'A' System, electric pumps ran 'B' Sytem.

Lol, as I said, I am COMPLETELY acquainted with the hydraulic system of the -200s, as I work on them every day.
I simply didn't (and still don't, thanks to you!) know WHICH series got the new bypass valve design. I'm assuming that it was an NG thing, because the gear is all new.

Quoting CALTECH (Reply 7):
Sssshhhhh, even worked on 737-100s. With aircraft airstairs FWD and AFT installed. Those were dinosaurs.

Okay, seriously, you're ancient. How's that 401(k) working out??
You must be talking about the PeoplExpress birds....... shudder.

I bet you never touched one with a gravel runway kit, though! Got ya beat there!
 
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HAWK21M
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RE: Steering Bypass Valve B737 Reliability.

Sat Apr 09, 2011 3:33 pm

Quoting CALTECH (Reply 4):

Educational & True.

Quoting CALTECH (Reply 7):

Sssshhhhh, even worked on 737-100s. With aircraft airstairs FWD and AFT installed. Those were dinosaurs.

The Aft Airstair was weird,housed with the LH Aft Entry Door.

regds
MEL.
I may not win often, but I damn well never lose!!! ;)
 
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CALTECH
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RE: Steering Bypass Valve B737 Reliability.

Sat Apr 09, 2011 4:59 pm

Quoting AA737-823 (Reply 8):
Lol, as I said, I am COMPLETELY acquainted with the hydraulic system of the -200s, as I work on them every day.
I simply didn't (and still don't, thanks to you!) know WHICH series got the new bypass valve design. I'm assuming that it was an NG thing, because the gear is all new.

The early 737-100/-200 IIRC had a retrofit, can't remember if it had a lever or pushbutton. The 737-300/-500 bypass valve has a push button that was depressed and a pin inserted into that button to keep it depressed and I believe it was different than the -100/-200 valve. The 737 NGs have a lever that gets pinned, like a rig pin. Know that they are different between the -300/-500 and the NGs.

Quoting AA737-823 (Reply 8):
Okay, seriously, you're ancient. How's that 401(k) working out??
You must be talking about the PeoplExpress birds....... shudder.

401(k) is doing quite well. Hope to be a multi-millionaire in 40 or 50 years, he he he.
Yes, PEOPLExpress had some old -100s. They were so small.

Quoting AA737-823 (Reply 8):
I bet you never touched one with a gravel runway kit, though! Got ya beat there!

Worked on Canadian International here in MCO. A few times, some of their 737s came in and had the gravel deflectors and vortex dissipators installed.

Quoting HAWK21M (Reply 9):
The Aft Airstair was weird,housed with the LH Aft Entry Door.

That was some monkey motion, that aft door and stairs. But it worked. Really liked that you could board those old planes from the ground.
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HAWK21M
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RE: Steering Bypass Valve B737 Reliability.

Tue Apr 12, 2011 10:25 am

Quoting CALTECH (Reply 10):

That was some monkey motion, that aft door and stairs. But it worked. Really liked that you could board those old planes from the ground.

Somehow the Airstairs on the B737.....Especially the Fwd ones were snag prone due to the limit switches sequencing Involved.
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