Making a leak free pvc storage canister to attach to my back plate

[elmer fudd]

I guess what I just don't understand is why you want it to be waterproof. From reading your comments, it sounds like you intend it to be a storage container that you will likely open up underwater. In that event, everything inside will become wet the instant you open it.

Now, I think you could easily seal it up with some o-rings and grease, but consider opening it up at 66'. Water pressure at that depth will be approximately 30 psi above the inside pressure of the container. Figure a 2" pipe cap has approximately 3 square inches of surface area, and you can see that it will take 90 pounds of force to pry that thing off of there in addition to overcoming the friction of the seal. An easy way to overcome this force would be to attach a male quick connect to it. When it comes time to open it, just disconnect your BC inflator, hook it to your container for a second or two and let the air pressure open it for you.

 

[UnderSeaBumbleBee]

No, I don't plan to open it up underwater. Where did you get that idea? Several emergency strobes on the market are notorious for flooding. If I make the effort to take one along, I would like for it not to be flooded. Also the elements in several of them are fragile so I would like to protect it to some degree. If you got the idea from the vacuum pressure comment that I made reference to after someone else brought it up, I was referring to any residual pressure after the container had been exposed to depth and returned to the surface.

For whatever reason and there are many, I would like to make a leak free storage container to carry items that I want to keep dry and or protected.

And sometimes people build things just because they can like this guy who made a robtic spider YouTube - Robot Spider I have been watching them for a while and it is pretty cool story. Anyway, I think my dry tube is a bit less ambitious and more practical. Although, if someone offered to let me drive the spider, I would not turn it down.

 

[elmer fudd]

I think it was just the fact that you were concerned about the difficulty of opening it. For some reason I interpreted that to mean opening it underwater.

Since you're only planning on opening it on the surface, I'd just try turning a piece of 2" pvc on a lathe and making one or two grooves for o-rings.

Another very easy option would be to take a 2" coupler, cut it in half, and then slide it up the pipe and glue it within an inch or so of the end. Simply put your cap on so it butts up flush with the coupler and wrap it once or twice with electrical tape.

 

[Hallmac]

There is an easier solution.

Glue the cap like you planned. On the same Isle as all the other fitting is an item made by Oatey

It is a pressure testing fitting.

2" GRIPPER [OAT 33401] - KSCDirect: MRO SuperStore

I have tested them to 250 psi.

Works well for making a cheap canister light too.

 

[UnderSeaBumbleBee]

Hallmac, that looks very promising! I looked on Home Depots website and they have a plastic version of that. I wonder if that would work? What do you think? If not I can always go to the plumbing supply house. I wonder how the galvanized material would stand up to salt water? I suppose ok as many tanks are hot dipped galvanized too.

I like the plug idea as it is easy and cheap and easily for others to duplicate.

 

[DIWdiver]

Since you played the chick card yourself, I was going to suggest you get some manly man to turn you a plug on his lathe. But it sounds like you may be able to do that yourself.

However, I like the idea of cutting the groves into the OD of the tube even better. That way you don't have to machine the inside of the tube to make it round and smooth (which it usually isn't on PVC).

I measured the OD of a 2" sch 40 pipe at about 2.380". If you used a 1/16" cross section o-ring, it would be a -035 size (nominally 2-1/4" ID), and your groove would be 0.105" wide by 2.280 diameter, which is about 0.050" deep. For a 3/32" o-ring, you'd want a -139 size (nominally 2-3/16" ID), but your groove would be 0.146" wide and 2.216" diameter, or about 0.082" deep. A 1/8" o-ring would be a -227 size (nominally 2-1/8" ID), and the groove would be .110" deep and 0.195" wide.

I think the 1/16" o-ring is too thin, and the 1/8 leaves too little material in the wall, which I measured at 0.155". So my recommendation would be the 3/32" one.

Since the pressure is low (for an o-ring) you can get away with a really soft one, like 50 durometer. That might be hard to find, but 70 duro is common. I wouldn't go any higher than that. Many scuba o-rings are 90 duro. I'd put two or three on, in grooves separated by about 0.150"

The cap is slightly tapered, so if you put three o-rings on, the outer one may be useless, unless you adjust the depth of the grooves to acomodate.

 

[DIWdiver]

Hallmac, that looks very promising! I looked on Home Depots website and they have a plastic version of that. I wonder if that would work? What do you think? If not I can always go to the plumbing supply house. I wonder how the galvanized material would stand up to salt water? I suppose ok as many tanks are hot dipped galvanized too.

I like the plug idea as it is easy and cheap and easily for others to duplicate.

I'm not thrilled with the idea of trusting important stuff to a device being used backward at well over 10 times its rated capacity. O-rings are designed for this kind of service. Still, the plug IS simple and easy!

 

[Hallmac]

Hallmac, that looks very promising! I looked on Home Depots website and they have a plastic version of that. I wonder if that would work? What do you think? If not I can always go to the plumbing supply house. I wonder how the galvanized material would stand up to salt water? I suppose ok as many tanks are hot dipped galvanized too.

I like the plug idea as it is easy and cheap and easily for others to duplicate.

The plastic version is what I use and tested. My hardware has held up well, and is easily replaced with stainless if yours does not come with it.

 

[Hallmac]

being used backward at well over 10 times its rated capacity.

Help me understand that because I must be missing something.

Schedule 40 is rated at 260 psi with a burst pressure of 890 psi and a working pressure of 166psi


**** never mind, I see what you were talking about**** the link I provided show a 5 psi test pressure. Thanks for pointing that out. Course, the use it is sold for may be the backwards use and it is 1/10 the strength of what it should be doing.

The lip will seal tighter as external pressure is increased, the seal will tighten as outward pressure squeezes in. In the opposite, the seal is the only thing holding it in place. As the internal pressure increased the cylinder expands since the seal will not expand the cylinder actually becomes bigger than the seal and it simply slips out.

I never saw that on the package when I bought it and as I stated I have tested it to 250 psi.

 

[UnderSeaBumbleBee]

Since you played the chick card yourself, I was going to suggest you get some manly man to turn you a plug on his lathe. But it sounds like you may be able to do that yourself.

If only I could find a manly man to do that for me! Alas, I have resorted to purchasing tools and am well known in the tool department! My Mother once gave me an air compressor for Christmas and it was one of the best presents ever! My married friends do not like me talking tools with their husbands. They say I put too many ideas in their heads. I say hey, if you want a project done, give the boy a new tool/toy. And viola, you project is on the way to being done. Everybody wins!

I played the chick card because I have small hands and was looking for something that I could easily open with cold wet tired hands. Something that might be easy for a guy with larger stronger hands might be too difficult for me so I was hoping that any design suggestions might take into account my lack of brute force. I think my original thought with the pvc screw plug would have been unworkable for that reason alone.

I like the idea of the plug and then a cap slid over the end to make it match the other end as well as to keep the T from snagging on anything.

You guys are the best! Thanks for all the helpful ideas! I am going to assemble a prototype tomorrow using the plug idea and hopefully if my friends have not already closed their pool for the season, test it out this weekend in the deep end! And if for some reason the plug alone did not work, I could always turn some groves into the pipe itself and it would be very much like what they guy did in the clip above.