Leakage detection


#1

How to do leakage detection?
In spite of doing a vacuum test which turned out really good, showing no leakage at all, i got some water inside the main tube today, causing a blackout and maybe damages.
How to detect weak points with leakage in the main tube? Any ideas? Soapwater and vacuumpump?
This is what happened:
Had a really nice dive today down to about 15m. Took it up and noticed some fog on the inside, i thought it might be ok with a second dive. I should have put in some dessiccant, but have not been able to get hold of any. Anyway, second dive went really well, we had the anchor exactly on a wreck site and descended with a loose plastic band around the anchor line as vertical guidance. When we have reached the bottom, i put in full speed back and succeded in ripping the plastic band to get free from the anchor line, just as planned. Then suddenly the screen went black, we tried restarting both browser and rov, to no avail. Back at the surface i noticed there was about 20ml seawater in the main tube, possibly damaged the electronics and caused the blackout. It might of course have been the batteries that have moved or whatever. I decided to go back home, disassemble all contacts and cards, rinse with alcohol, blow with air and set to dry. Hopefully i will get it back running.


#2

@marcus2,
Sorry to hear about your accident. Make sure that you use 92% or better isopropyl alcohol. I got mine at Walmart.
I have vacuum tested my OpenROV WTC to better than 15 inches of Hg over greater than 15 minutes so far.
Regards,
TCIII AVD


#3

Thx for your sympathies @TCIII !
Yeah, i know about the iso… But i only had denatured alcohol available at home (Sunday here in Sweden and nowhere near to get iso today), i rinsed all components and connectors thoroughly with that and then blew it dry with the compressor. Now parts are left separated. Maybe i should have put them in the oven too, but i keep my fingers crossed that it may be revived anyway. I am even not sure that it died because of the leakage, it could also have been the batteries or the caps that may have gotten out of position and lost connection. I have the somewhat badly designed battery tubes for the 2.7. The endplugs have a tendency to pop out… No signs of leakage there , though. I have bought 2.8 tubes which i will swap to before next dive. I am thinking of vacuum test the main tube (wo electronics) in the sink might be a good idea for trying to get a grip where it could be a leak or a weak point.


#4

@marcus2 sorry to hear about the leak.

Soap water and a vacuum pump does work well to find a leak. You can also do a visual inspection of all the o-rings and make sure you have a strong seal. If you can narrow down the problem to the caps with o-rings or the epoxy that would help determine the next course of action.

You did the right thing drying out the electronics and fingers crossed that things will work. If things are not working as whole you can test the individual components to narrow down the damage.

Good luck and let us know how it goes.


#5

Yeah, @Brian_Grau is right, soap and water goes a long way. I remember we tested about 50 tubes by putting one end in a tupperware with water (that covered the endcap) at a time. We could then narrow it down to which endcap. Then we could watch carefully and see if was the main o-ring or the epoxy pass through, or even the laminates…tough to catch.

Often times there is water in the tube after a deep dive in cold water that is actually condensation from the humidity in the environment. For that we recommend a fresh desiccant pouch with each dive. Gotta be fresh otherwise it might release moisture.

Lastly I might recommend checking the o-ring gland for any dips or cracks that might have been caused by the gluing process. Tiny cracks or “crazing” usually doesn’t leak water but a divot from the laser cutting process, although rare, can be the culprit.

Z


#6

Desiccant works for condensation and very small leaks. But when you get 20ml the desiccant is going to be overwhelmed and the water will move around as you recover the ROV. In that case some silica gel such as a feminine napkin or small diaper will grab the water and stop it from moving and doing more damage.


#7

Yay!

Positive update here; after reassembling all electronics (no visible corrosion or oxidation anywhere, at least what i could see) everything is back on track and works as expected, the only thing i notice is that i have seem to lost the simple theme plugin, but i believe that i only have to reinstall it again.
Will update here when i have performed leakage detection.