Hydraulics

[northloughshore]

Could repeated running of a hydraulic system cause overheating of hydraulic fluid? if so what would be the possible implications of this?

[A321COBI]

yes it could, imps/consequences: loss of cabin pressure/oxygen, engine explosion/ overheating and failure

[bearfoil]

Good question, however as hot as carbon ablative brakes get, I do not think the fluid even boils, let alone ignites (without ignition source).

[northloughshore]

hm I was wondering more about perpetual running of a service say gear that keeps cycling up and down continually. I expect like any fluid there would be expansion and like you said heat generated. Would heat alter the properties of the fluid?

[A321COBI]

evaporation of the fluid is a common problems on aircraft and one I have had to deal with

[mad_jock]

Aye it can and does.

This from a hydralic ram side of things with earth movers and diggers.

If its old fluid it will have a fair bit of water in it which will boil and cause cavitation in the pumps. which knackars them pretty quickly. If it really gets hot you will start melting seals.

Hydralic fluid is dangeous stuff when hot it sticks to you like nepalm and has quite a large heat capacity. I was never brave enough to do the last couple of threads of the tank plug with my fingers and try and snatch the plug from dropping in the 50 gallon drum.

From a flying side of things I have had a pump explode in the hot section dumping the entire lot in there and thankfully it didn't go on fire. Produced vast quantities of smoke though.

[A321COBI]

From a flying side of things I have had a pump explode in the hot section dumping the entire lot in there and thankfully it didn't go on fire. Produced vast quantities of smoke though

what kind of aircraft was this on mad jock

[mad_jock]

to answer you second post it would be fine. You have diggers working 24h shifting max operating weights. The only time they start over heating is if something goes wrong or the cooler gets bunged up.

[northloughshore]

gotcha, I Like the parable of the digger! I wouldn't expect maintenance schedules would allow too much water in hydraulic systems on an aircraft but then again you never know. Thanks

[fantom]

A320. Let us imagine, after landing, Y sys runs the aft cargo door opening and fails to shut off. It takes about forty minutes to overheat and pop the cb. You are about to call for engine start...

You then have to wait an hour or so for the sys to reset.

Buggah.

[hetfield]

Could repeated running of a hydraulic system cause overheating of hydraulic fluid?

Yes, that's why aeroplanes have hyd overheat warnings.

[mad_jock]

Sorry fantom I am not familar with the A320.

Is it the actual fluid temp which is causing the problem or is it an electric pump which is over heating and popping the CB?

[bumpyflight]

electric pump heating

[Mr @ Spotty M]

A number of aircraft have what you could call heat exchanges in the fuel tanks.
The hydraulic fluid passes through the matrix/heat exchanger which cools the fluid down.
Not uncommon for a minimum fuel quantity to be required inside fuel tanks, to allow hydraulics to be operated.

[mad_jock]

How much Hyd fluid do the jets carry?

Say A320, 737, A330, 767, A340, 747

[bumpyflight]

not a fixed amount, depends on flight time, height and so on, like fuel

[mad_jock]

Ruff guess then. So i take its consumable?

Sorry I fly a BAe heap of a turbo prop which if they need to top up any of the vital fluids between checks its cause for concern.

[Right Way Up]

bumpyflight,
What is your background?

[muduckace]

Could repeated running of a hydraulic system cause overheating of hydraulic fluid? if so what would be the possible implications of this?

As long as the design of the aircraft is respected on the ground not common at all, in flight not a chance given a properly working aircraft. As said above some aircraft have heat exchangers in the fuel tanks requiring a minimum amount of fuel for cooling most just rely on the hyd lines expelling heat and at altitude it is cold enough out where even the aircraft with fuel heat exchangers do not really need them.

Now the most common cause of an overheat is due to an actuator failure where fluid that is normally contained on either side of a piston slips by at super high speeds thus friction thus heat.

All aircraft I know of have a means of monotoring hyd temp, if you are concerned about long term usage on the ground just keep an eye on the temperature and give her a break if need be.


Implications.

The pumps and seals take the highest toll soo pump failure, component failure or leakage is possible.

[Right Way Up]

Was there not an Air France A340 that burnt out because of continuous running of an hydraulic pump on the ground.

Edited to add: ASN Aircraft accident Airbus A340-211 F-GNIA Paris-Charles de Gaulle Airport (CDG)