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Old 27th August 2016, 12:13 PM
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RobF RobF is offline
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Join Date: Mar 2010
Member of: Southampton Buccaneers, Parkstone, South Dorset
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Posts: 10,170

Originally Posted by Nomads HFT View Post
Today I tested one of my piston seals for friction at 20C and 46C.

At 20C, the static friction was 6.07N (Newtons), the kinetic (sliding) friction 4.38N

At 46C, the static friction was 10.6N, the kinetic friction 7.35N

I had a second seal in my TX cooking in the greenhouse, and when acclimatised to 46C, the muzzle velocity was the same as at 20C.

For comparison, Rob's unsized seal was nearer 23N at 40C (much higher), down to under 5N when sized.

Worth bearing in mind that the kinetic friction figures quoted exist only for a very short period of time at the very start of the stroke; when the cylinder air pressure increases, they rocket.
very interesting. The new rig is on long term test. It's not getting touched for a good while to see its temp sensitivity with the sized seal.

Steve pope told me before the comp that it sounds like seal fit issues.
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