[solved] Vacuum Pump Leaking

water-proofing
solved

#1

Hello, recently I tested my seal for the end-caps with a hand vacuum pump. At first it seemed to be airtight, however after a minute or so I could tell that the dial had moved down very slightly and continued to fall very slowly. I want to emphasize that it was a very slow decrease but was noticeable after a few seconds of staring at the dial. I wanted to know if this loss of negative pressure equates to a leak or if it will still be watertight since the pressure loss was extremely gradual and slow. Also I want to add that my seal is similar to previous times when no water leaked in.

Thanks
-Sam


#2

It depends on what vacuum pressure you are testing at and what depth you intend on sending the ROV. A seal that doesn’t leak at 5m depth may very well leak at 50 or 100m. Here’s a neat calculator to help you decide what pressure to test: http://www.calctool.org/CALC/other/games/depth_press

Another possibility is that the seal between the vacuum pump and housing has a leak, so be sure it is sealed properly.


#3

We ran in to a lot of false leak indicators because we were using the suction cup adapter that fit over a wider area rather than a pen tip adapter that would go directly in to the syringe hole. Turns out that the top layer of the endcap if not well sealed can have micro paths for air to come in from the outer edge.

@Walt_Holm suggested that the issue can often be fixed by applying the vacuum and then applying a little bit of acrylic cement along the outer seem of the end cap so that the vacuum would pull it in and effectively seal those air channels.


#4

Thanks that did the trick @badevguru


#5