View Full Version : B737 Hydraulics Queries

Callsign Kilo
25th Mar 2010, 13:32
My Q's relate to the NG, however I don't think there is a lot of differentiation between that and the classics?

First of all I have read that a number of hydraulic fuses are installed within particular hydraulic lines in order to preserve fluid for other components should a leak develop. Are these restricted to the braking system (normal and alternate) LE flaps and slats, nose gear and thrust reversers? If so, why is this? Is the chance of fluid escape rate greater?

Secondly, the PTU operates when a drop in pressure output from the B system EDP is sensed (among other factors). Is the PTU just additional redundancy for autoslat operation i.e in a stall scenario?

Thanks guys for you input

25th Mar 2010, 18:49

I will answer your first question as a general one, because most aircraft I have been involved with, not the B737, have hydraulic line fuses built into the brake systems. One aircraft also has a fuse in the oleo.

The chance of a tyre failure tread shedding could well wipe out the brake flexible lines and also on a B747 the oleo strut pressure gauge.

Right after take-off, highest odds, with a brake pipe failure, there would be a total loss of that systems hydraulic oil. With the line fuse, perhaps fitted into the antiskid unit, would be closed after detecting the downstream pressure drop thus restricting total oil loss to that system. Applicable brake(s) would now be inop.

The B747 main oleos have a pressure gauge that could also be damaged if a tyre again was to fail, in this case the oleo strut pressure would be lost collapsing that leg, so an internal fuse is built into the strut to maintain the pressure after gauge lost.

I am not qualified to answer your second question on the PTU but it does sound close to the mark, B737 people to quote exact details for this please.


Spendid Cruiser
26th Mar 2010, 05:14
Da daaaaa (http://www.b737.org.uk/hydraulics.htm#Fuses) :)