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'O' Ring Groove Sizing

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Colin Heseltine	26/08/2023 19:55:01
744 forum posts 375 photos	I have a hand pump on a Stuart 504 boiler. The pump does not seal over well. It used to have graphite yarn as a seal but this had dried and gone brittle so replaced with an 'O' ring. Still not a very good seal. I am thinking of putting an 'O' ring on the piston itself. The piston is 0.624" dia. and the bore is nominally .625". I have silicone 'O' ring which is .625" OD and .4375 ID. Is this a good idea and if so what groove dimensions should I use (width and depth). Many Thanks, Colin
JasonB	26/08/2023 20:30:31
25215 forum posts 3105 photos 1 articles	Is that actual size or nominal size? My thought s are that it is a nominal 3/32" ring with actual cross section of approx 0.103. Typical size for model use from Model Engineers Handbook would be groove width of 0.125" and depth from cylinder 0.098" which is approx 5% compression
Colin Heseltine	26/08/2023 21:36:53
744 forum posts 375 photos	'O' ring is 5/8" OD and 7/16" ID Macc Models no. 111. Colin
Huub	26/08/2023 22:13:16
220 forum posts 20 photos	I use the this PDF/handbook for o-ring & groove dimensions Parker O-ring dimensions
JasonB	27/08/2023 06:50:29
25215 forum posts 3105 photos 1 articles	That's the nominal sizes then and nominal 3/32" section So my sizes will be OK of model use. The thing with many makers/suppliers charts is they are for much higher pressure use which results in far too much friction for our use in things like model engine cylinders and feed feed pumps. The figures I gave are based on tests done by Arnold Throp (Fleet Coreliss fame)

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