Originally Posted by chewy
No need for pressure relief valves if your auto inflation system cuts off at the correct pressure.
Why is it "proper" to fit them on tubes.
Well Chewy, this is where you and I will have a serious disagreement. On quality mil spec or commercial boats here (N. America) and there (Europe) over pressure relief valves are not unusual. This goes back to the quality of the boat you own. Some manufacturers omit this due to additional cost, I imagine the better ones don't. Most of the "recreational" boats i've seen don't have them but then, I haven't been everywhere. Consider this: Perhaps your boat is in the water on a cool day and you top off the tubes because they have gone soft. A common occurrence. Next day you pull it out and put it on the trailer, sits a few days and perhaps you get a hot day in the middle of the week. If you have dark tubes and it gets hot enough, not having pop off valves could be a real problem. The pressure will continue to increase as long as it keeps getting warmer. Now this does depend on your climate, maybe it doesn't get very warm over in the U.K. but here in the States and elsewhere it can get very warm.
My boat has nine pressure relief valves preset at 3 1/2 pounds, one advantage of having them is while inflating them you never have to worry about over-inflating them, no matter what your auto inflation system does.
I do not regret having this feature as a new set of sponsons (tubes) is quite pricey... I do believe pop off valves extend the life of the sponsons as well although I don't have any hard data, just my opinion, everybody has one.
After checking the average high/low temperatures the U.K. receives, it appears overpressure due to heat would never be a problem, not much variance. Or warm for that matter, how do you guys deal with that?