Changing the tank thread

[pisauron]

Hello,

I recently found some strange tanks. On first glance it seems to be a cheap Chinese composite tank. We have 3 of them.

But once you try to fit it with a valve you run into problems. And we failed to find a valve for it. It's seems the manufacturer made a mistake.

The tank sticker says M18x1.5? So what! It's sure ain't that. Try M25? Nope. Try 3/4? Nope.

I took it to a shop specialized in bolts and they think it's might be M24...but don't have this in stock.

Suppose it is M24 - is there a valve for it? Never seen one yet. Do you know of any?

But what of I strip the threads and tap a new thread? The closest one seems to be M25x2... Will this make the tank dangerous for use? Do people do that?

Will love to find a solution with your help.

Thanks

 

[Tanks A Lot]

This is indeed a Chinese cylinder, from Acecare.

You are also correct that this is definetly not an M18x1.5, because its female thread would have a minimum minor diameter of around 16.68mm. Your measurement of 21.81 fits well within the range of the M24x2 minor minimum diameter, which should be around 21.84mm. However, only thread gauging can accurately very this. A caliper is not up to the task and me from a keyboard far away is certainly no better.

It is disappointing seeing a high pressure piece of equipment so carelessly labeled.

Re-tapping is not a wise choice. I'm not comfortable doing it on "normal" aluminium cylinders and I would never attempt doing it on a composite cylinder. A composite cylinder already has a very thin liner to start with, taking any material off it is not a wise choice.

From a purely engineering standpoint, I'd wager that re-tapping it would be just fine, as the carbon fibers are what give the most strength, not the aluminium itself. However, your biggest problem will be machining a proper O-ring gland into your newly tapped thread. This isn't a straightforward process, as a very slight taper of usually 5° is employed.

I have never seen a cylinder valve with a M24x2 stem. Dräger does use the M24x2 thread for the cylinder to regulator connection, but that won't be of any help.

Pictures are deceiving, but it looks to me like someone already seriously messed up the threads.

If you want my advice, call it a day and throw this one out. Whatever you might able to achieve is not worth the considerable risk you are exposing yourself and others to.

 

[pisauron]

This is indeed a Chinese cylinder, from Acecare.

You are also correct that this is definetly not an M18x1.5, because its female thread would have a minimum minor diameter of around 16.68mm. Your measurement of 21.81 fits well within the range of the M24x2 minor minimum diameter, which should be around 21.84mm. However, only thread gauging can accurately very this. A caliper is not up to the task and me from a keyboard far away is certainly no better.

It is disappointing seeing a high pressure piece of equipment so carelessly labeled.

Re-tapping is not a wise choice. I'm not comfortable doing it on "normal" aluminium cylinders and I would never attempt doing it on a composite cylinder. A composite cylinder already has a very thin liner to start with, taking any material off it is not a wise choice.

From a purely engineering standpoint, I'd wager that re-tapping it would be just fine, as the carbon fibers are what give the most strength, not the aluminium itself. However, your biggest problem will be machining a proper O-ring gland into your newly tapped thread. This isn't a straightforward process, as a very slight taper of usually 5° is employed.

I have never seen a cylinder valve with a M24x2 stem. Dräger does use the M24x2 thread for the cylinder to regulator connection, but that won't be of any help.

Pictures are deceiving, but it looks to me like someone already seriously messed up the threads.

View attachment 889615

If you want my advice, call it a day and throw this one out. Whatever you might able to achieve is not worth the considerable risk you are exposing yourself and others to.

Thank you very much for the advice!

I am also not comfortable with re-tapping the thread. The aluminum layer will lose half it's size by my eatimate and I don't see the black carbon layer on the neck, only aluminum+glass fiber. It will be sketchy. At 300 bar it will be a bomb

On the other hand the tank should go into hydro anyway so the structure could be tested. But still scary. These chinese tanks don't give me much confidence even before messing with them. I have seen one loose the at the buttom once.

I have found some mention on google for a M24x1.5 thread for tanks, but couldn't find a valve. Maybe a medical oxygen valve? There must be a reason for 3 tanks like this to exist...

As for the threads I don't see anything strange but I am not good at this yet. It's a bit of dirt on the first threads.

Well to the garbage it goes...

 

[pisauron]

@Tanks A Lot

I wonder would it be possible to use a thread adaptor?

 

[Scared Silly]

It is disappointing seeing a high pressure piece of equipment so carelessly labeled.

It is not mislabeled. The cylinder has already been tapped to have larger diameter.

Here is what the opening should look like on the same 2l Acecare cylinder. Note: the groove for the o-ring.

For the OP, you are dealing with a high pressure cylinder that has been already modified. IMHO it is garbage.

 

[pisauron]

It is not mislabeled. The cylinder has already been tapped to have larger diameter.

For the OP, you are dealing with a high pressure cylinder that has been already modified. IMHO it is garbage.

That's interesting I haven't thought about that.
It is defently a possibility. Why M24 we will never know...

Thanks

 

[Capt Jim Wyatt]

I would strongly consider taking these to a scrapyard or making a bell or a flower planter out of them.

 

[pisauron]

I would strongly consider taking these to a scrapyard or making a bell or a flower planter out of them.

Great idea. But i think cutting it with the glass fibers will not end well.
Tommorow they go to the garbage or some fun project for sure.

 

[rjack321]

Hello,

I recently found some strange tanks. On first glance it seems to be a cheap Chinese composite tank. We have 3 of them.

But once you try to fit it with a valve you run into problems. And we failed to find a valve for it. It's seems the manufacturer made a mistake.

The tank sticker says M18x1.5? So what! It's sure ain't that. Try M25? Nope. Try 3/4? Nope.

I took it to a shop specialized in bolts and they think it's might be M24...but don't have this in stock.

Suppose it is M24 - is there a valve for it? Never seen one yet. Do you know of any?

But what of I strip the threads and tap a new thread? The closest one seems to be M25x2... Will this make the tank dangerous for use? Do people do that?

Will love to find a solution with your help.

Thanks

I have 5 of them and these are indeed made in M18x1.5

As noted by others, the threads were already modified in a dangerous way. The aluminum is a key part of their design and these are scrap now. Drill a hole in them to be on the safe side and off to the landfill.

 

[pisauron]

I have 5 of them and these are indeed made in M18x1.5

As noted by others, the threads were already modified in a dangerous way. The aluminum is a key part of their design and these are scrap now. Drill a hole in them to be on the safe side and off to the landfill.

Are you happy with your 5? do they hold well?

I think i will order me a new one with the correct thread.