We have an AUV with a 6" inner diameter non-locking enclosure, Blue Robotics flanges and end caps. We recently started pool testing. The flanges start to pop out almost immediately in the sun, even before running the motors. We used a Mittyvac pump to do an indoor test (without any extra heat) and the flanges start to separate at about 2psi. We cleaned all the excess silicone grease from the flanges/enclosure. Then we replaced the orings and used barely any silicone grease. This made no difference. We just ordered a PRV adapter so we can pull vacuum before going in the water next time. Is there anything else we can do?
Hi @Gina -
2 psi can happen from the thermal expansion of air pretty quick! That pressure is just a bit over what a humans lungs can produce, and for the internal 6" face of an endcap, results in a force of over 50 lbs!
The easiest fix is to keep your enclosure out of the sun - a towel over it is sure to help, and hopefully the water you’re testing in isn’t too warm. Making that towel wet would help - water is after all so much more thermally conductive than air!
With that said, to produce 2 psi the temperature in there has increased quite a lot! If you started at ~72F, you’d be reaching about 144F to produce that temperature! 62C may not be too hot for an internal CPU temperature, but perhaps your heat is coming from other internal sources, like a computer with a fan?
A fan would certainly help move air around to help that heat leave - as would using aluminum end cap plates and/or directly coupling your heat sources to them.
The Sun is quite a powerful heat source for a clear enclosure. It probably accounts for half the power helping that air expand, and so if you’re using 30 watts or so this would just keep happening…
Securing the endcap flanges externally (or internally) with fasteners and structure that can take the 100 lbs of expansion force is another solution, assuming your contents can take the heat!
Thanks for your quick reply! One more question: Do we need equipment other than a PRV and backfill adapter to pull vacuum in our enclosure? We got our Mittyvac pump from a Marine Technology Society grant in 2024, and it did not come with the vacuum barb and hose - we purchased those items separately.
Hi @Gina -
You should be set with those parts to pull a vacuum - and that will definitely keep things shut! However, with a lot less air inside, heat will also have a much tougher time moving away from your electronics - vacuum is an incredible insulator! Keep an eye on your CPI temp!