captain wrote: ↑
Sat Feb 03, 2018 11:40 am
Does the seat have a hole in the center of it. The hole is supposed to stop it from extruding. It's possible some valves were rebuilt with the incorrect seat.
Yes, there is a hole in it. This is actually the correct seat specified for the J-valves.
I remember hearing the same story about the hole preventing extrusion, but it really doesn't make sense to me. Because these were only used on the J-Valves (no hole in the K-valve seat) it leads me to believe the problem they were trying to solve was being cause in some way by the reserve system. I would like to know more facts about the reason for the hole.
Really look at the actual path of air pressure coming from a fill hose with the tank valve closed. It enters the hole, potentially letting pressure get between the seat and the carrier. When the tank valve is then opened the air flow from the fill hose exerts pressure behind the soft set. It is not all that unusual for that pressure to push the soft seat outward from its normal position, holding it against the orifice. I think it's possible the soft material shrinks a little with age and gets just loose enough in the carrier to dislodge. I have seen it a number of times.
Same thing can happen with line valves that are subjected at times to air flow from the "wrong" direction. We see hundreds of Sherwood type line valves when dealing with fill systems from fire departments, dive shops, etc. Commonly see a few each year that are installed contrary to correct air flow because of convenience in positioning of the male and female threads on the valves. With time and a lot of use they can exhibit very similar issues with extrusion, and there are no holes in them. The air pressure from reverse flow is able to get around behind the seat and result in partial extrusion. Only see one or two a year.