A short history about Skydrol
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Always wondered over the years as to why the RAF's hydraulic fluid of choice, OM-15, was never used in the civil aviation world given it's far more benign towards humans and materials.
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Both good and bad with Skydrol. Significantly reduced the fire hazard from hydraulic fluid leaks. But Skydrol fluids are also hard on the skin of service technicians, and require special seal materials and any paints/coatings that will come into contact with the fluid.
The current approach with aircraft flight control actuation systems is electro-hydrostatic actuators (EHA's). This is a sealed, self contained hydraulic actuation circuit pressurized by an electric motor driven pump. Much less prone to leakage.
The current approach with aircraft flight control actuation systems is electro-hydrostatic actuators (EHA's). This is a sealed, self contained hydraulic actuation circuit pressurized by an electric motor driven pump. Much less prone to leakage.
It certainly will burn under the right conditions. On the only engine fire aftermath I have seen, the skydrol had turned into a dark brown, glutinous treacle like substance.
I also recall the atmosphere in the hydraulic bay on TriStar aircraft was always oppressive with skydrol mist/fumes.
I also recall the atmosphere in the hydraulic bay on TriStar aircraft was always oppressive with skydrol mist/fumes.
Ah Skydrol! First ran into Skydrol 7000 (green juice) in mid-1950's when it was used in cabin superchargers of DC-6 and DC-7 aircraft. It had better lubricity than mineral fluids. When you opened the bottom hatch aft of the #1 and #4 engines to check the cabin superchargers, you had to be careful not to look up at it as sure as anything, a leaked drop would target your eye. Milk was the best thing to neutralize it. And yes, as a techie you spent a lot of time washing your hands BEFORE relieving oneself than in the sanitizing after. One of our customers, I think it was Alitalia, used 7000 in the aircraft hydraulic system. Notably, no Constellations were converted to Skydrol as they would have been unapproachable with their leakage.
The 707 and DC-8 jets brought us Skydrol 500 (purple shade). Private Jet is right in that the Hydraulic Compartment on the L-1011 Tristars could be uninhabitable. I've seen pinhole spraying leaks that left everything in there saturated and dripping. You literally needed respirators.
Worst I ever experienced though was an Eastern Air Lines DC-9-30 at KEWR that had an internal leak through the system relief valve. The fluid badly overheated and turned into a black revolting gunk. The smell was so bad several mechanics actually upchucked from breathing fumes after opening lines. I nearly did too, it was absolutely stomach churning. We changed just about every component in the left hydraulic system and did lots of flushing of the lines. Overheated brakes could also cook the fluid but the quantity being below the lockout deboosters was nothing like a whole system.
Pin-hole leaks are dangerous in any high pressure system, gaseous or fluid. They may be nearly invisible even in a fluid system. Passing a hand or arm through it and can end with an embolism or fluid under your skin and even severing of digits although I am happy never to have seen that. We were specifically warned of that on the Britannia which had the highest system pressure I ever worked on. It of course used mineral fluid.
With regard to the soles of shoes, one fellow techie bought a new pair of ankle-high work bots with corrugated rubber soles. He worked that first night while changing some hydraulic component in the wheel well and consequently continually stepped in a Skydrol puddle. Next day he pulled them out of his locker. The soles had expanded sideways and in thickness. They looked like the shoes of clowns in the circus or could have doubled as snowshoes.
The 707 and DC-8 jets brought us Skydrol 500 (purple shade). Private Jet is right in that the Hydraulic Compartment on the L-1011 Tristars could be uninhabitable. I've seen pinhole spraying leaks that left everything in there saturated and dripping. You literally needed respirators.
Worst I ever experienced though was an Eastern Air Lines DC-9-30 at KEWR that had an internal leak through the system relief valve. The fluid badly overheated and turned into a black revolting gunk. The smell was so bad several mechanics actually upchucked from breathing fumes after opening lines. I nearly did too, it was absolutely stomach churning. We changed just about every component in the left hydraulic system and did lots of flushing of the lines. Overheated brakes could also cook the fluid but the quantity being below the lockout deboosters was nothing like a whole system.
Pin-hole leaks are dangerous in any high pressure system, gaseous or fluid. They may be nearly invisible even in a fluid system. Passing a hand or arm through it and can end with an embolism or fluid under your skin and even severing of digits although I am happy never to have seen that. We were specifically warned of that on the Britannia which had the highest system pressure I ever worked on. It of course used mineral fluid.
With regard to the soles of shoes, one fellow techie bought a new pair of ankle-high work bots with corrugated rubber soles. He worked that first night while changing some hydraulic component in the wheel well and consequently continually stepped in a Skydrol puddle. Next day he pulled them out of his locker. The soles had expanded sideways and in thickness. They looked like the shoes of clowns in the circus or could have doubled as snowshoes.
Last edited by tonytales; 19th Nov 2016 at 22:31.
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Now you know why mechanics wash their hands before going to the toilet. Something may be itching a while otherwise...
Skydrol is very irritating and slippery, but not nearly as unhealthy as engine oils and other greases we use on daily basis.
It can cause serious damage to your body if you are exposed to a stream of 3000PSI, that's the same as a waterjet cutter.
I also ask myself how they dispose of waste hydraulics (it looks like a brown smudge after it's been used).
Skydrol is very irritating and slippery, but not nearly as unhealthy as engine oils and other greases we use on daily basis.
It can cause serious damage to your body if you are exposed to a stream of 3000PSI, that's the same as a waterjet cutter.
I also ask myself how they dispose of waste hydraulics (it looks like a brown smudge after it's been used).
