O-ring leak in shallow water


Hi. We have just done a test on the E-tube. The O-ring, however, leaked in shallow depth. We put it in a the sink with both endcaps on and the water went into the tube. We also test it with one cap on, and put the water inside the tube, and the water leak to outside. The situation is shown in the pictures.



Sorry to hear that you have had an O-ring leak. The o-rings can leak for a few reasons:

  1. There is dirt, silt or some other small particle on the O-ring or O-ring Channel. Even the smallest dust particle can cause the seal to fail. Be sure to thoroughly clean the O-ring, as well as the channel on the end cap that it sits on, as well as the inner diameter of your acrylic tube. Be sure to use an o-ring that is free of imperfections, use a very small layer of lubrication, and make sure it slides in entirely and doesn’t get caught on the corner of the tube. If it does, you will need to chamfer the edge some more.
  2. There could be a scratch on the tube. Even the smallest vertical scratch will create a channel for water to flow through. When this happens it usually occurs during the chamfering step of the build. If this is the case you will need to replace your e-tube.
  3. The o-ring could be sized improperly- But based on the size of the seal from the pictures you provided, it looks like your seal is the right size, I would say it is safe to rule this one out.

Let me know if you need more help! Hope you are able to resolve this issue.


Nima Torabi
OpenROV Support


I found that some people use teflon tape, SILICONE and even ballon to strenthen the seal, which method may be more effective ?



We don’t recommend any of those methods for reinforcing an o-ring seal. The best seal is a simple one, where everything is exceptionally clean. The mechanics of the o-ring seal work best with nothing sitting between the o-ring and its sealing surface. Under pressure, the o-ring compresses and creates a stronger seal. That is why if there is dust or a scratch on a the seal surface, then under pressure water will find its way in anyway. Please look at this diagram to see what I mean.

You should have received extra o-rings with your kit, replace them if necessary. And if you have any scratches on the edge of your acrylic tube you will want to replace it, as it is never going to be fully water tight again.


What acrylic cement are you using to connect each layer of the endcaps? Did you make sure to fully cement each layer together? This looks like a lot of water for a scratch or some dirt… Maybe there’s a much larger problem such as each of the caps not making a full seal together or the syringe not being cemented or epoxied in place.



Especially examine the bottom of the O ring groove. At low pressures an O ring preforms basically as a gasket so surfaces need to be smooth. If you find roughness often a coat or two of lacquer like fingernail polish will help, once all grease is removed.