Watertight Enclosure, Flange Dimensions and O-ring Selection

I am in the process of designing a battery housing for my newly designed rov.

I did a lot of research on the forum and on the internet.

I designed an enclosure according to the battery pack I will produce with the trelloborg program and underpressure program.

I would like to hear your opinions on this subject before we move on to the production phase.
This issue actually scares me a little bit as the enclosure I am designing will have a high capacity package inside.

The maximum depth of the enclosure I designed is 400 meters. Also this casing will have 3 radial o-rings. I will use Buna-N AS568-452 70A o-ring.

You can see the dimensions and output of the flange and housing I designed below.

You can also see the output of your 4" flange and housing in the trelleborg program below.

I also do not plan to use an end cap. I will use a direct flange cap and fix it to the housing with bolts.

In the images below you can see the design and the output of the underpressure program. Since I did not use an end cap, but a flange cap, I entered the plate free diameter value as the inner diameter of the flange. Is this correct in your opinion?

Do you think there is a problem with these dimensions?

When I compare it with the dimensions of the 4" housings you produce, I see that there is no problem, but your opinions are very important. Do you think this housing will leak even if it is produced in the dimensions I want?

I also do not plan to use an end cap. I will use a direct flange cap and fix it to the housing with bolts.

After producing this design, I will pressure test it and share the results with you.

Thank you in advance for your reply.

Best regards,

First problem is the amount of O-Ring races. You are going to create a pressure zone between each of the races and the end flange will not go on. Been there done that on one project.

Hi Harold,

Thanks for the information.

According to what you mentioned it would be more useful to use 2 o-ring slots instead of 3 o-ring slots. do I understand correctly?

When I originally posted I was thinking the flange would be non-vented. As long as you have a vent plug somewhere you should be ok.

There is no real advantage to having a ton of O-ring races. If you want added withstanding pressure you can use what is called a Parbak along with the O-Ring. You would have to change your race model.

Take a look at this link: Sealing Solutions

At the bottom of the page you will see Mobile Inphorm O-ring calculator. I have used this tool in the past many times to design seals for various applications. I have penetrations in all three of our hydrostatic pressure vessels and this program has been used to seal design in for all of our tanks with the highest pressure going to 2100 psi. This tank was proof tested to 2750 psi so I know without a doubt I have had seal designs go to that pressure.

I don’t know where you are located but Parker seals O-rings etc. World wide so again I highly recommend their tool.

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Thank you for your reply, Harold.

I will look into the Mobile Inphorm O-ring calculator.

I actually have a limited amount of time to get this product into production.

Therefore, I would like to continue with a ready-made o-ring.

So I designed the flange and housing according to the o-ring I chose.

I will reduce the 3 o-ring slots to 2 and I plan to start production.

As far as I understand from what you mentioned, you do not see a problem with the dimensions in the flange and watertight enclosure tube design I made.

It will be enough for me for this sealed tube to enter 400 meters.

Considering the o-ring I will use and the dimensions in the design, do you think the watertigh enclosure I designed will leak?

By the way, of course I will use a vent or pressure relief valve on the end cap.

Your opinions are very valuable. Thanks for your help.

When you grease your O-rings, do not do bigger the glob better the job or you will more than likely flood. Have just enough of a film to wet the surface and that should be it.

The only thing I don’t like is the 6061 because it will powdered over time. We use it as a quick and dirty pressure cap alternative in our hydrostatic pressure tanks. You might consider getting the plate and tube anodized.

I would suggest a lead in chamfer on your tube ends so your O-rings will get gently compressed as you put the flanges on and greatly reduce the risk of nicking an O-ring.

Makre sure that they screws that you are using are not going to create cathodic corrosion issues and I would worry about 6061 being a soft material … that your screw threads, without helicoils, are going to get chewed up over time. Can you make a mounting ring on the end … basically increase the tube diameter so you can have room to put in helicoils etc.? Heck for that matter you could put a flange O-ring race in and that would be almost pay dirt for a pirmary seal.

Just a lot of things still bug me and I hate to see you toss some money into the trash once you find out the hard way. If nothing else on the threaded holes for the end consider using anti-seaze or a high pressure grease to coat the threads.

Hi Harold,

I have updated the drawings according to your feedback and the measurements in parker mobile iphorm.

I have given up on the hex nut slots, I will not use nuts to tighten the connectors, I will drill a tapped hole directly into the flange

I was happy with the outputs I saw after making this update. But the O-ring inside diameter scretch value is very low. When I put the o-ring on the flange, there is almost no change in the inner diameter of the o-ring. There is an expansion of 0.08 percent. Do you think this is a problem?

Do you think I should increase the groove diameter to increase the strech value of the o-ring inner diameter? If I do this, the strech value will increase, but the total compression force value increases too much. That’s why I’m afraid of not being able to open the flange after closing it. Or I’m afraid of an explosion when opening it with a vacuum pump.

I will also use the flanges 7075 series and I will directly tap the flanges for the connectors. Then I plan to do a type 3 anodized coating.

Your feedback is very important to me. Thank you in advance for your help.

Also, if you know someone who can produce this flange and tube, I would be very grateful if you direct me to that person.

Outer diameter of tube 325, inner diameter 304,8 length 700mm.