Pressure testing shows slight pressure loss


#1

After completing assembly I did the pressure test to 15 mmHg and within 2-3 min. it dropped to 14mm
I submerged the tube and while under vacuum I noticed a little water around the O ring. What should
I do, if anything?


#2

Can you post pictures of the o-ring and where the water is. Also how were you conducting the vacuum test?


#3

I don’t think I can get a good picture of this, the O ring has a tight seal just as shown in your instructions and I used the vacuum tester just like it shows in your instructions. After I submerged it for about 30 min. I noticed a small drop inside the tube and noticed that 1 endcap shows water around the O ring. Both O rings show a 1 mm pressure seal against the main tube.


#4

Off the top of my head I can think of two possible reasons for the drop in pressure.

First, I am not sure which version of OpenROV you have but there was a small imperfection in the laser cutting process on some units a while ago. Check out this other forum post and check to make sure that this is not leading to the issue.

Second, the way the vacuum test is being conducted it is possible to have a small drop in pressure even if there is no drop in pressure in the tube. If the outside 1.5mm white acrylic piece and the larger 6mm clear piece do not have a cementing job that covers the entire surface, air can travel between these layers and thus have the decrease in pressure.


From an operational standpoint there is no issue if this is the cause of the decrease in pressure.

The test of the electronics is a very good way to see if water is getting into the tube.

One last comment would be that when you open and close the tube water can sit on the inside of the tube and it can appear that there is a drop of water on the inside but it is left over from opening the tube.


#5

Thank you so much for all your help. Since I actually found water drops inside the main tube before
opening it, I was certain that I have a small leak. I found that the cable feed through is the problem
because I wrapped some soft paper around the cables to absorb any possible water and then
submerged it with a 15 mmHg vacuum making sure the cable feed through is on the top and would
not absorb any water from any other possible leaks. After about 15 minutes I checked it and now
I had no water drops inside, but the paper was completely wet. I know I sealed the cable very well
even using a small pinpoint heatgun to heat the epoxy giving it a better flow and to eliminate any
possible air pockets and moving the wires around while potting it and then heating it.How can I fix
this leak? I thought about cutting a part of a larger syringe and building a 3/4" tall collar around the
cables and the filling it with epoxy. Is this a workable solution or can you make any other recommendations.