How much air is my inflatable hot tub losing?
October 16, 2021 3:42 PM   Subscribe

I have an inflatable hot tub that will not stay fully inflated. About everyday, I have to attach the air pump to get it firm from about 70-75% firm. I found a place around the air valve that seems to be where the leak is coming from, but I need some help to be confident this is it.

I soaped up the spot and watched a bubble form while I timed it. In 53 seconds, the bubble grew to about 2 5/8 inches. Granted, half of the bubble couldn't form because it was attached to the side of the hot tub. But since I can't find any other leaks, I wonder how fast is it losing air and is it losing enough air that it would lose 25-30% of its volume in 24 hours?

Also, if I patch it, should I patch it when it is firm and fully inflated? How will that affect the patch when I empty the hot tub to clean it?
posted by CollectiveMind to Science & Nature (4 answers total)
Response by poster: Also, how many cubic feet of air fills a round, inflatable 4 person hot tub?
posted by CollectiveMind at 3:53 PM on October 16, 2021

Leaks can go pretty fast. If you can put your face by where the leak is, you will probably be able to feel the air coming out. (that's how I find a hard-to-find bike tube leak.)

Check the manufacturer's directions for patching. I would assume patch it while it's deflated so the pressure of air escaping doesn't ruin the seal of the patch, but I am not an expert.
posted by blnkfrnk at 4:09 PM on October 16, 2021

Best answer: I don't know anything about hot tubs or patches, but the bubble you found corresponds to around 2 cubic meters of air at standard atmospheric pressure per day. Or half that, if the bubble is a hemisphere. (Using a volume of 4/3 pi radius^3 in 53 seconds.) If the inside of the hot tub is a few cubic meters at a few times atmospheric pressure, losing 25% in a day seems pretty reasonable for that one leak.

If you measure the inside and outside diameters and height of the tub, you can estimate the volume. Guessing the pressure is harder, unless you happen to inflate it with an air pump that has a pressure gauge. A bike tire is usually around 3-4 atmospheres, and I'm guessing a hot tub is squishier than that, so multiply the actual volume by something like 2-3 to get the amount of gas at one atmosphere required to fill the whole thing.
posted by eotvos at 4:10 PM on October 16, 2021

Best answer: Always apply patches when it's deflated. If you do it while it's inflated, a bubble of air will work its way through the adhesive to the edge, creating a path for more air to escape. Press the patch on really firmly all over, and then give it time to cure before reinflating.
posted by pipeski at 4:24 PM on October 16, 2021 [2 favorites]

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