Creating an Airtight Tank: Tips and Techniques for a Successful Design

[Loochia]

Summary: Help!

For my freshman engineering in design class, my group is trying to make an airtight tank that can withstand some pressure that is pumped in. For our prototype, we built a tank out of acrylic sheets and glued it together with epoxy glue, but it popped the second we pumped a little air inside. Does anyone have any suggestions as to other methods of created an airtight tank? Different materials, glues, etc?

 

[berkeman]

(thread moved to the schoolwork forums)

Welcome to the PF.

Well, making a pressure vessel with flat sides seems to be the first problem. Can you say why?

Once you fix that problem, what kinds of joints do you think you should use to improve the strength of the seals? Do you have access to a CNC milling machine or a 3-D printer?

 

[Loochia]

How would we make a pressure vessel without flat sides? Like a cylinder?

We were thinking of switching our glue to acryilc cement and/or using hot melt adhesives. What do you think about these changes?

We have access to a 3-D printer and I believe there is a CNC milling machine in the workshop.

 

[berkeman]

Like a cylinder?

Yes. Starting with a tubing-like material gets you the rounded sides, but the top and bottom are still problematic. Can you mate hemispheres with the tubing to make a more traditional pressure vessel shape? Can you add bracing members outside of the structure? What are the rules/guidelines for this project?

 

[MCTachyon]

A cylindrical vessel with hemispherical or 'dished' heads (like those shown above) is close to the best shape you can use for a pressure vessel (theoretically, a sphere would be best).

Usually you want what is holding the vessel together (the glue in this case) to be of similar, or close, strength properties of the material being used. Notice in the Google image results above this is typically a full penetration weld or rivets when steel is the case.

If the cylinder can be seamless with just the heads fitted on, this would be as perfect as you can get.

Hope this helps.

 

[russ_watters]

For my freshman engineering in design class, my group is trying to make an airtight tank that can withstand some pressure...

How much pressure? What is this device going to be used for? Do you have aa professor advising/supervising on this project?

 

[Filip Larsen]

If you continue to use angled joins (i.e. a box) you may want to absorb some of the pressure using tension bands tightened around the sides, like near the edges and perhaps also at center. This assumes the material of the sides are capable of some plastic/elastic deformation without rupturing.

If you get into the problem where the box can structurally hold the pressure but the seams leak you may want to consider using an internal balloon that gets inflated inside the box.

For safe pressure testing you really should consider using water instead of air, as the energy release in case of failure is much less for water. If you only have an air pump you can fill the box with water so only a tiny fraction at top is air and then use the pump to pressurize a very small volume only.

No matter what you do be mindful of safety at all times when pressurized. Use goggles and safety distance (like use a water hose filled with water right up to the pump to keep persons at safe distance while pressurizing).

Edit: corrected that my fingers spelled goggles with double o instead of g

 

[256bits]

Summary: Help!

For my freshman engineering in design class, my group is trying to make an airtight tank that can withstand some pressure that is pumped in. For our prototype, we built a tank out of acrylic sheets and glued it together with epoxy glue, but it popped the second we pumped a little air inside. Does anyone have any suggestions as to other methods of created an airtight tank? Different materials, glues, etc?
View attachment 253053 View attachment 253054

Great learning experience, as to why some things are made the way they are made ( for optimization of what you want to optimize - which might be material cost, fabrication, durability, maintenance, ease of use, safety( ie rupture, leakage), volume and/pressure in this case. )

Square box is OK if there is no other criteria, such as who can make a vessel to hold the most pressure.
You just have to figure out a way to stop leakage ( rubber seals at the joints ( corner problematic ), or some silicon sealing ), gaskets, etc ).
Holding the box together- banding as mentioned by @Flip Larsen., clamps on the parallel faces, welding, etc.

I think you have found out that glue is limited in its ability.
I wouldn't consider that a failure, but as one of the steps in the design procedure towards an end result.