O-Ring for penstock bulhead (dish-end)
O-Ring for penstock bulhead (dish-end)
(OP)
Hi folks,
I have to provide a 1500mm dia hemispherical bulkhead to close a penstock unit of the same size. I have already designed and fabricated a hemispherical bulhead with flanges. I specified the material of O-ring as NBR/ EPDM/ Delrin/ Peek.
The whole assembly was to be tested in shop with 130MPa of test pressure. AT 105 MPa pressure, the leakage started. On opening we noticed that NBR seal has cold-flown and completely gone out-of-shape.
What material do you suggest for such high pressure application? This was first intercourse with O-Rings and it ended up in a failure. Actually I asked the suppliers and they said NBR will meet the requirement. What am I missing?
I should have asked earlier...but still not too late.
Thanks.
I have to provide a 1500mm dia hemispherical bulkhead to close a penstock unit of the same size. I have already designed and fabricated a hemispherical bulhead with flanges. I specified the material of O-ring as NBR/ EPDM/ Delrin/ Peek.
The whole assembly was to be tested in shop with 130MPa of test pressure. AT 105 MPa pressure, the leakage started. On opening we noticed that NBR seal has cold-flown and completely gone out-of-shape.
What material do you suggest for such high pressure application? This was first intercourse with O-Rings and it ended up in a failure. Actually I asked the suppliers and they said NBR will meet the requirement. What am I missing?
I should have asked earlier...but still not too late.
Thanks.





RE: O-Ring for penstock bulhead (dish-end)
Your problem is most probably related to the gap the O-ring must seal-the higher the pressure, the smaller the gap must be. O-rings will seal thousands of PSI, but the gap must be small or the elastomer will flow. This is elementary O-ring sealing. Get Parker's O-ring manual!
RE: O-Ring for penstock bulhead (dish-end)
RE: O-Ring for penstock bulhead (dish-end)
Yes, I see a gap of around 2mm on 10.5MPa pressure, through which the seal is flowing. Will any workaround like metallic backing strip work?
RE: O-Ring for penstock bulhead (dish-end)
RE: O-Ring for penstock bulhead (dish-end)
http://www.gtweed.com/85256D3C0038D8DA/vwContentByKey/N25PFPN9221ELETEN
The spring energized gasket may also be considered.
http://www.helicoflex.com/products.htm
A square cross section with 2 backup rings may work. Also using backup rings with your existing O-rings may be viable solution. The also have spring energized o-rings.