Boeing (767) brake accumulator pressure gauge explanation and other brake questions

[RandomPerson8008]

Hi,

I have a quick question about the 767 accumulator pressure gauge.

Does this gauge actually measure pressure of the inert gas pressure in the accumulator instead of of hydraulic pressure itself?

I understand that the accumulator will normally indicate about 3000 psi when the normal or alternate brakes (R&C hydraulics) are operative and the accumulator contains inert gas, as normal. In the absence of R or C hydraulic pressure, it will indicate accumulator inert gas pressure.

Is it true to say: If there is a problem and the accumulator leaks its gas, the accumulator gauge could read 0 yet the normal or alternate brakes are still functioning normally? When might it read 0? Only during brake application, or would it read 0 continuously if the accumulator leaked its gas?

Also, it's my understanding that anti-skid is only available for normal and alternate brakes. Is this correct? It would seem that reserve and accumulator breaking would be using the same brake lines, and might still have anti-skid, but the manual says otherwise.

Thanks.

[Capt Quentin McHale]

Random,


"Does this gauge actually measure pressure of the inert gas pressure in the accumulator instead of of hydraulic pressure itself?"


From my interpretation,(engineers please correct me) it actually reads both. With hyd's pressurised, it is reading system press, approx 3000psi. With hyd's depressurised, the pressure indication will gradually bleed down over time (a long time) to read the accumulator gas precharge pressure, approx 1000psi. I believe a quicker way to read the accumulator gas pressure is to pump the brake pedals about 10 - 12 times, with hyd's off, to bleed system pressure down to accumulator gas precharge pressure (brake pedals go flat ie. no resistance).


Rgds McHale. :)

[RandomPerson8008]

Thank you Captain McHale. Subsequent to my initial post, I discussed this with an engineer and he explained it the same as you have. As I now understand it , the lowest the gauge should ever read is ~1000 psi unless there is a problem with the accumulator. However, if there is a problem that causes the gauge to read 0, this reading has no impact on brake operation as long as C or R hydraulic system pressure is still available.

My only remaining question is whether or not accumulator brake application provides anti-skid through the alternate brake system, it appears that reserve braking would since it is functionally the same as alternate braking.

[flite idol]

Anti skid works for all brake sources. (Unless switched off if switch installed or a fault.) In normal it works on individual wheels, in all other modes it acts on lateral wheel pairs together.(axle pairs.)

[RandomPerson8008]

Thank you flite idol.

[flite idol]

You are welcome Random, you had it figured out your self anyhoo!