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26-11-2006, 12:40 AM #16
Re: Replacement fo CO2 Bulk Tank refrigeration unit
Hi NH3LVR,
Yep, I survived. It was a good day. I hope yours was also.
My best answer on the relief valve weeping is that the valves are manufacturered with a tolerance. Some of the rupture discs (the industrial ones, not the ones by Hansen, Henry, etc.) can be purchased with different tolerances.
If you order an industrial /process rupture disc you can get them with I believe a 2%, 5%, or 10% tolerance. The higher tolerance (2%) means the disc will not rupture until the disc is exposed to 98% of the design pressure. They are very tight.
The lower tolerance disc (10%, if I remember my numbers properly) means the rupture pressure is 90% of the disc rating.
Mechanical relief valves are similar (although I don't remember the exact numbers right now . but I think the tolerance for a relief valve is 10%). When the operating pressure gets to within the tolerance of the valve it starts to simmer. Essentially, the way I read this is the disc in the valve floats a little, which causes the valve to weep some vapor.
Originally Posted by NH3LVR
I'm assuming you are talking about the Rego valves for the underlined text?
Rupture discs are a good idea, but you have to de-rate the relief valve capacity if a rupture disc is used upstream.