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Hydraulic seals help
JeffHs - 8/6/15 at 04:05 PM

Does anyone know the correct name for the lipped seals usually found in master and slave cylinders? I'm trying to source some for an odd application and can't find them online - it doesn't help that I don't know what they're called!

Dingz - 8/6/15 at 06:22 PM

Usually just called lip seals, for piston or rod use, or equi-lipped which will do both. Usually the dynamic lip is shorter than the static. Assuming you are using std brake fluid you will need them to be in EPDM material.
Although having once bought an expensive Wilwood cylinder I was suprised to discover that they just use cheap and cheerful O rings which will always weep in that application!

JeffHs - 8/6/15 at 07:02 PM

Thanks for reply. It's for an aircraft application using OM15 a superfine mineral oil so the seals will be nitrile. It begs another question though. Why did the automotive industry use brake fluid instead of mineral oil? The old bits (60s) I'm using have no corrosion or wear unlike anything you would find on a similar aged car.

Dingz - 8/6/15 at 07:27 PM

Citroen of course until recently always used mineral oils for brakes and suspension systems. I don't really know why automotive went for the Glycol based Dot fluids, they absorb water, attack paint need different materials for seals and hoses, needs to be changed regularly. It has a higher temperature range though than the older mineral oils and probably the Americans said it must be used.
Commercial Aircraft use Skydrols which are even nastier but don't burn. I believe military planes use mineral oils though.

britishtrident - 8/6/15 at 07:32 PM

quote:
Originally posted by JeffHs
Thanks for reply. It's for an aircraft application using OM15 a superfine mineral oil so the seals will be nitrile. It begs another question though. Why did the automotive industry use brake fluid instead of mineral oil? The old bits (60s) I'm using have no corrosion or wear unlike anything you would find on a similar aged car.


This link is interesting but doesn't say why
http://www.carhistory4u.com/the-last-100-years/parts-of-the-car/brakes

v8kid - 8/6/15 at 09:24 PM

quote:
Originally posted by britishtrident
quote:
Originally posted by JeffHs
Thanks for reply. It's for an aircraft application using OM15 a superfine mineral oil so the seals will be nitrile. It begs another question though. Why did the automotive industry use brake fluid instead of mineral oil? The old bits (60s) I'm using have no corrosion or wear unlike anything you would find on a similar aged car.


This link is interesting but doesn't say why
http://www.carhistory4u.com/the-last-100-years/parts-of-the-car/brakes


I vaguely remember it has to do with water absorption. You can't stop condensation and glycol absorbs water up to a point and won't let it freeze into a solid lump blocking the brake pipes. Also although glycol does lower its boiling point with water it is still higher than a water globule in a pipe.

Up to a point is the critical bit.

Would like to know the proper story though.

Cheers