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? :confused:

[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) (http://aviation-safety.net/database/record.php?id=19940120-0)

[Admiral346]

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

Complete bull!

It gets serviced, refilled to a limit and so on. It is not dependent on the variables above and in no way like fuel...

Nic

[Right Way Up]

Admiral,

If you look at bumpys posts (all made today) there is not a lot of sense being made! :rolleyes:

[Admiral346]

How much Hyd fluid do the jets carry?

I don't know exactly, but I have been told it's not a whole lot. Force is crosssection by pressure, and those 3000psi are doing the job - saves weight!

Nic

[Right Way Up]

Max fill for an A319.

Green 14.5L, Yellow 12.5L & Blue 6.5L.

Amount reflects the amount of users each system has. Green sys powers landing gear retraction for example.

[muduckace]

Amount reflects the amount of users each system has.

It only reflects the amount in the resevoir, the system contains alot more.

[glhcarl]

Max fill for an A319.

Green 14.5L, Yellow 12.5L & Blue 6.5L.



It only reflects the amount in the resevoir, the system contains alot more.

The A320 series (318-319-320-321) hydraulic systems hold 235 Liters (62 Gallons) of fluid:

100 liters (26 gallons) in the Green system.

75 liters (20 gallons) in the Yellow system.

60 liters (16 gallons) in the Blue system.

[Right Way Up]

Glhcarl & Muduckace,

Thanks for the info. You learn something new every day!!:ok:

[freespinner]

Fluid cooling by fuel heat exchanger is a Boeing concept. Airbus uses fluid cooling by flow thru metal tubing exposed to outside air.

[mad_jock]

Thanks for that I did wonder about hyd fluid as a consumable.

Thanks for the data. Do Boeing types use more of the stuff for a similar sized aircraft?

And for the orginal OP on my type the hyd temp warning comes on at 90 deg C.

And large earnthmovers/diggers the operators have been known to cook chickens on the hyd tanks.

[411A]

Complete bull!

It gets serviced, refilled to a limit and so on. It is not dependent on the variables above and in no way like fuel...
Second the motion on the complete bull...wonder where some guys get these ideas?
As for total quantity, seem to remember 48 USGallons total hydraulic fluid capacity on the L1011.

[Spanner Turner]

From the 747 Maintenance Manual;


CAUTION:
DURING OPERATIONS INVOLVING HYDRAULIC SYSTEMS PRESSURIZATION, RELATED INSTRUMENTS AND INDICATING LIGHTS IN THE FLIGHT COMPARTMENT SHOULD BE CLOSELY MONITORED TO ASSURE SATISFACTORY OPERATION OF SYSTEM. IF HYDRAULIC FLUID OVERHEAT CONDITION OCCURS, SYSTEM OPERATION SHOULD BE DISCONTINUED.
DO NOT OPERATE TRAILING EDGE FLAPS MORE THAN TWO CYCLES IN A 15 MINUTE PERIOD. SYSTEM LOADING CONDITIONS CAN OVERHEAT HYDRAULIC FLUID.

Check for a minimum of 300 gallons (2000 pounds; 900 kilograms) of fuel in each No. 1 and 4 main fuel tanks, and 805 gallons (5400 pounds, 2450 kilograms) in each No. 2 and 3 main fuel tanks.
NOTE: If the applicable tank has the minimum amount of fuel, there is no time limit on the operation of the hydraulic pump. If there is less fuel than the minimum amount, the hydraulic pump operation is limited to 15 minutes.

CAUTION: TO PREVENT HYDRAULIC FLUID OVERHEAT, DO NOT OPERATE PUMPS AFTER OVERHEAT LIGHT COMES ON OR LONGER THAN 15 MINUTES WITHOUT MINIMUM QUANTITIES OF FUEL IN TANKS. ALLOW 20-MINUTE COOLING PERIOD AFTER 15-MINUTE OPERATION OR AFTER OVERHEAT LIGHT GOES OUT. WHEN AMBIENT TEMPERATURE EXCEEDS 100¡F, OPEN NACELLE STRUT FAIRING DOORS. EXTREME TEMPERATURES AND LOAD CONDITIONS CAN OVERHEAT HYDRAULIC FLUID.


The above outlines operations in the Maintenance environment and it would be extremely unlikely to encounter a hydraulic overheat and near to impossible in a "Flight" condition. But like anything in aviation, "It's possible"

:ok:
.

[Jetdoc]

some aircraft have heat exchangers in the fuel tanks requiring a minimum amount of fuel for cooling

Not all of the hydraulic fluid passes through the heat exchangers. Only the portion of the hydraulic fluid that circulates through the pumps for cooling and lubrication is passed through the heat exchangers.

[Flash2001]

Read "Fate is the Hunter" , "A hole" and Gann's memory of Ross and the matches.

After an excellent landing etc...

[BOAC]

In my considered and learned opinion, bumpyflight is yet another in the outbreak of pests we have seen lately. Must be the warm weather. Best ignored?.

[heavy.airbourne]

As I recall, AF recycled an A340 this way: Forgot to switch off the pump, towed her around CDG, overheat condition led to a/c fire which was damaged beyond repair and written off.

[glhcarl]

Not all of the hydraulic fluid passes through the heat exchangers. Only the portion of the hydraulic fluid that circulates through the pumps for cooling and lubrication is passed through the heat exchangers.

Doesn't all the hydraulic fluid pass through the pump sooner or later?

[no-hoper]

5080 psi system on A380 requires more cooling.There are 2 double air-oil
heatexchangers with hyd motors driven fans (ground & low speed).As a
backup 2 fuel-oil heatexchangers are installed.

[Jetdoc]

Doesn't all the hydraulic fluid pass through the pump sooner or later?

Yes of course it does, however, within the pump, a small portion of the fluid is diverted to circulate around the pump for cooling and lubrication. If you happen to be standing around any Boeing and the engine cowlings are open, look at the hydraulic pump. You will see 3 lines. One is supply, one is pressure and the last one is marked case drain. This is the cooling and lubrication drain. That fluid is routed through the fuel tank heat exchanger before returning to the reservoir. The hydraulic fluid used to do the actual work returns directly to the reservoir and is cooled as it passes through the return lines.

[mad_jock]

It was that drain return which caused the incident I had with the base plate seperating from the pump body pulling the studs from the casting. A none return valve packed in and became a valve in the closed position q a whore of a lot of noise a big bang and tons of smoke. Our ginger was in the back as well when it blew. It was the most emotional and expressive I have ever seen him with a tech problem.