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.

Quote Originally Posted by NH3LVR
I believe we are only coming to notice this problem using NH3 now that we have alarms on the relief valve lines. The cheap aluminum valves used on some compressor packages have always been a problem.
I think you are right. Before (back in the good ole days ) the relief valves were essentially forgotten until they let go.

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.