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Master Cylinder Seals and Design

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Arthur Beloso View Drop Down
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Joined: May/27/2018
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    Posted: May/27/2018 at 6:28pm
Hello everyone. I am having some problems on the design of our new master cylinder. In the last prototype we used EPDM o’rings to seal the brake fluid. But the lifetime of the o’ring is way too low, like 4h in the maximum. I though in use some U-ring’s but I don’t have sure if this change can improve the lifetime. I saw that commercial master cylinders use piston cup and some kind of u-ring.
Usually the pressure it is around 8 Mpa (1160 Psi), but it can be higher since it is used in racing . We use an 11.5mm bore diameter, but it is changeable to any size avaible of seal. The master cylinder is made of aluminum.
There is any better type of seal that I can use? Do you now any book that can give me more information about it?
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Nick914 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nick914 Quote  Post ReplyReply Direct Link To This Post Posted: May/29/2018 at 8:12am
I'd guess surface finish is the culprit for your lifetime issue. The shape of the seal won't resolve it.
Cup seals is the way to go on the front side of the cylinder, O-ring on the back. Makes a one-way valve, easier bleeding.
Nicholas Lefebvre

Universite Laval
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Arthur Beloso View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Arthur Beloso Quote  Post ReplyReply Direct Link To This Post Posted: May/30/2018 at 9:48am
Thanks for the help ! I will do a study of the rugosity inside my master cylinder body ( and piston as well ) to see if it is inside the recommended.
But, by Cup seal you mean one like this ? ( I'm having some troubles in the translation to Portuguese to find the equivalent one of U-Cups/ Cup seals / Piston Cups)

http://forums.bajasae.net/forum/uploads/4743/2.png



Edited by Arthur Beloso - May/30/2018 at 9:52am
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Nick914 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nick914 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/08/2018 at 7:46am
That would be it, yes
Nicholas Lefebvre

Universite Laval
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