Skydrol contamination in Fuel

[ross_M]

I saw this quote in a FAQ on the Skydrol website. I was wondering how do they figure that 5% contamination is a worst case scenario?

Skydrol.com - Frequently Asked Questions

Q: What happens when fuel is contaminated by hydraulic fluid?

A: In laboratory tests, concentrations of up to 5% Skydrol in jet fuel were cooled to -30oF. No gel formation or any other effect was observed. 5% is the maximum concentration possible in the worst case of a leak in a fuel tank heat exchanger.

[sb_sfo]

You're going to have a minimum fuel amount in the tanks for hyd. cooling, and a maximum quantity of hyd. fluid in the system that is being cooled in that tank. Assuming that it all gets pumped into the fuel tank, which it probably won't, from there it's just simple math, no?

[ross_M]

Duh! Stupid me.

That's how they get that number. Interesting. Order of magnitude does 5% make sense though? I know it'll vary between aircraft but is the ratio of total hydraulic fluid inventory to minimum fuel amount close to 5%?

Thanks!

[safelife]

Most hydraulic systems found on aircraft have a total volume between one and three gallons.
Anything higher than 5% won't last for more than a couple of seconds really...

[munster]

The 737NG A system Contains about 22 litres of Skydrol! You'd have to get the left wing tank below 350kg to achieve a 5% mix.

[ross_M]

Gotcha! So 5% is an overly conservative estimate. It'd be hard or well almost impossible to approach that ratio in any reasonable scenario.

Thanks!

[rmm]

Bear in mind that it's usually just the pump case drain line that is routed thru the heat exchanger not the main supply or return lines. At least on Boeing's anyway.