Tanks - aluminium vs steel

[barracuda]

I know there have been a lot of discussions on this topic but I wanted to share the following :

We bought 12 litre aluminium tanks from the authorised dealer (since gone bust) of Sherwood in singapore. First year there were absoulutely no probs. 2nd year the tanks started leaking at the neck and some water went into the tanks. We cleaned the same out, dried the tanks and changed the O rings and the leakage problem reduced considerably but did not vanish completely.

I read somewhere that alimunium tanks should be inspected visually by taking the valves off every 2-3 months. To me this does not make sense as the metal is quite soft and doing this can actaully result in the threads wearing out fast.

I did try contacting sherwood but their australian office just refused to acknowledge the problem. The company was recently bought over by Cramer Decker and upon contacting their technical dept, I was told that I would need to send one tank all the way there for them to do anything about it. This is not a viable option for me due to the various problems assoicated with customs, import/export rules and regulations, etc in India where I live so I just dropped the whole thing.

I have got to a point where I am thinking of just buying steel tanks in the future but would be happy if soemone out there can give me some advise on how to fit new valves on the tanks for the first time (the supplier had precious little info on this!!) as well as how to properly take care of the tanks in the future.

venkat
barracuda diving india

 

[turnerjd]

Originally posted by barracuda
2nd year the tanks started leaking at the neck and some water went into the tanks. We cleaned the same out, dried the tanks and changed the O rings and the leakage problem reduced considerably but did not vanish completely.

I read somewhere that alimunium tanks should be inspected visually by taking the valves off every 2-3 months. To me this does not make sense as the metal is quite soft and doing this can actaully result in the threads wearing out fast.

I suspect that you have a different problem. If there is a problem that allows water past the valve threads - the tanks aren't going to hold pressure are they???????

Now, if you have water in the tank I suggest it has come from one of 3 other sources...

1 the compressor - check your filters very carefully and make sure that no moisture is getting into the tank.

2 You are breathing the tanks empty. Now, if you breath tanks totally empty and are not careful a small ammount of water can then (theoretically) get in.

3 If you fill in a water bath - sloppy procedure such as filling whips falling into the tank will slowly introduce small ammounts of water into the tank - equally, having a wet tank valve will alow small ammounts of water in. - over a year this can soon add up!


I really don't think that if water can get past the threads then the tank would be able to hold full fill pressure. What realy clinches it is that you said that after you changed the o-rings it was better - I suspect that is is just a slow process - a little bit at a time, if you went back to your tanks at the end of the second year you would probably find a similar ammount of water as at the end of the first year.

I have never heard of testing aluminium tanks every 2-3 months. In the UK it is still every 2 years, and tanks from suspect alloys have to have an eddy current test on the neck region.

As for Al vs steel - if you have a moisture problem then going from Al to steel will make things worse. Try and find out exactly where the water is getting in first.

Jon T

 

[greg somers]

The most likely culprit is the compressor filter.
In New Zealand the tanks get their valves removed yearly by law.Once for visual and the next year for the hydro.
There is a problem in the industry when it comes to compressors.My local dive shop owner also is the main agent for new compressors for the entire Australasian region and when I did my compressor and tank filling training,he taught it.Because compressors are expensive equipment and require a regular preventative maintenance schedule,some dive shops are inclined to cut corners.This includes not changing the dive filters as often and also they try to repackage the filters themselves,but there are very few technicians in the world who are capable of doing it properly.Another problem is because the cost of a new compressor can be prohibitive,some outlets go for compressors that are too small for the job and they get worn out quicker and need more maintenance as they get overused according to their specifications.A busy dive outlet should have a compressor that will cost over $100,000 New Zealand or $40,000 US as a minimum with a regular logged maintenance schedule which includes filter replacement.They become clogged with hydrocarbons and water and then don't work anymore.Maybe change where your air gets filled and ask to see the compressor and where the intlet pipe to source clean air is situatted.
Cheers Big Ears,
The Gasman.

 

[Thomas Ivey]

Originally posted by barracuda
I know there have been a lot of discussions on this topic but I wanted to share the following :

We bought 12 litre aluminium tanks from the authorised dealer (since gone bust) of Sherwood in singapore. First year there were absoulutely no probs. 2nd year the tanks started leaking at the neck and some water went into the tanks. We cleaned the same out, dried the tanks and changed the O rings and the leakage problem reduced considerably but did not vanish completely.

I read somewhere that alimunium tanks should be inspected visually by taking the valves off every 2-3 months. To me this does not make sense as the metal is quite soft and doing this can actaully result in the threads wearing out fast.

I did try contacting sherwood but their australian office just refused to acknowledge the problem. The company was recently bought over by Cramer Decker and upon contacting their technical dept, I was told that I would need to send one tank all the way there for them to do anything about it. This is not a viable option for me due to the various problems assoicated with customs, import/export rules and regulations, etc in India where I live so I just dropped the whole thing.

I have got to a point where I am thinking of just buying steel tanks in the future but would be happy if soemone out there can give me some advise on how to fit new valves on the tanks for the first time (the supplier had precious little info on this!!) as well as how to properly take care of the tanks in the future.

venkat
barracuda diving india

If the tanks started leaking as stated in your thread. I assume you saw bubbles coming from the tank/valve area. Them have a reputable local dive store take a look at it, asked them to use an o-ring specified by the valve manufacture. Have them fill it and check for bubbles.

If this is not the case, I agree with the others, you are receiving bad air fills.

ti

 

[barracuda]

hi all,

thanks for your replies and advice.

the possibility of the tanks being emptied is remote as we monitor the same very carefully and it is only very rarely that some guest take it down to perhaps a low of 30 bar.

similarly the filling hose falling in water is not probable due to the staff who fill the same are very responsible.

i do agree the filter could be the culprit but i personally change the same every 100 hours of operation. (before you gasp in horror, i would liek to mention that we have a major problem with spares and have to manage with available spares without jeopardising quality or safety.) Barring a few droplets of water in the last chamber, there does not appear to be any water going through the filter itself.

to me it still appears taht the O rings are the problem as there is bubbling at the top where the valve meets the tank. unfortuantley i cannot take the tank to anyone else as there IS no one else where we are located in india !! so it is very much down to me how i can manage and take care of the stuff. this is the main reason i was real glad to get on this website so that i could get the benefit of expert advice as well as experience.

 

[turnerjd]

Originally posted by barracuda

i do agree the filter could be the culprit but i personally change the same every 100 hours of operation. (before you gasp in horror, i would liek to mention that we have a major problem with spares and have to manage with available spares without jeopardising quality or safety.) Barring a few droplets of water in the last chamber, there does not appear to be any water going through the filter itself.

I suspect (and this is only an I suspect) that if you have a few drops in the final chamber then there will be quite some ammount that will have made its way through to the tanks as a fine mist - It might be worth investigating having some form of pre-condensor loop put in to try and physically condense as much moisture as possible before the filter stack - this might involve getting a local mechanic to make something up (put it before the filter stack and it should be OK) - if you need an idea I can draw something that should work

to me it still appears taht the O rings are the problem as there is bubbling at the top where the valve meets the tank. unfortuantley i cannot take the tank to anyone else as there IS no one else where we are located in india !! so it is very much down to me how i can manage and take care of the stuff. this is the main reason i was real glad to get on this website so that i could get the benefit of expert advice as well as experience.

You also said that the tanks never go below 30 Bar.
Now, with 30 bar in the tank, slowly tring to creep out, and water (being pushed by atomspheric pressure at 1 bar) trying to go the other way, I would suggest that this is unlikely - even at depth (30m = 4Bar) I would say this is unlikely

As for the poor seal between tank and valve, talk to the tank manufacturer and the valve manufacturer (I assume they are different) to make sure that they are compatable, also ask exactly what spec O-ring they recomend. The other thing to do, and I would try and do this quite urgently, is to use a thread tester to see if the threads in the tank neck have stretched. If they guage goes in more than 1/2 a turn then stop using the tanks strait away!

You said that the tanks were bought from sherwood - have a look at the original markings, and I am sure they are made by Luxfer (a british company although probably made in their US plant as they were distributed via sherwood) It should say this in the markings on the tank. If it does, then I can give you the contact details for Luxfer head office, gas cylinder head office, or any range of their offices who should be more than qualified to help you! they have a good web presence as well - the only email address for luxfer diving cylinders on their web page is helen.zarate@luxfer.com.au .I don't know if they have a diving specific web page - this is from their parent company web page.

Whilst running a dive operation in some far away inaccessible place has always been a dream of mine, I can sympathise with you in your lack of technical support from manufacturers etc.... Good luck finding the problem, although I suspect you have more than 1 problem here.

Jon T

PS, for the pre condensor loop you need something to cool the air, and collect any water/moisture that is condensed - if you have something made as a one off - put it on the INLET to the compressor so it isn't a pressurised part, and also it doesn't need to be specially clean etc.. as this is what the filters later on in the chain are for. At the minimum you want a long metal inlet pipe that once it arrives next to the compressor has at least 2 - 3 metres (coiled!) in a cold water bath, and a water trap at the end to collect condensed moisture.

 

[greg somers]

The specification code for luxfer tanks is an international standard and they will hold the patent and engineering specifications for them.Quote the Luxfer no. of the tanks and they will be able to email you the exact engineering specs for those tank models,and you will be able to check them to see it they are out of the operating standards.
Regards

 

[barracuda]

hi turner,

would appreciate your info on the pre condensor loop and contact details of Luxfer. your guess is right. the tanks are from Luxfer originally. will try my luck with them and also recheck the final filter stage for leaks.

the tank K valves have also given us trouble. while i understand the abuse some guests inflict on the tank valves by forcing them more than necessary, this particular batch appear to be really delicate. we do have some old steel tanks with different K valves which have really stood the test of time and are in perfect shape.

all our valves bar a couple as well as the tank neck O rings are from Sherwood. I might have forgotten to add that the tanks are only 3 years old and we actually use them only for around 6 months each year !! now you can understand why i am royally pissed off !

shall await your reply to take further action. regards.

 

[turnerjd]

I generally have a poor opinion of sherwood, in future, if you want GOOD quality tank valves may I suggest in order of preference,

Apeks - yess Apeks make more than just regs!
AP Valves (the 'Buddy' range of equipment)
MDE (England)

The americans on the board I am sure will be able to tell you the good / better American brands of tank valves.

In general the tank manufacturers sell tanks bare (no valve) and then the dive shop puts the valve in. Almost all valves go on any tank (provided the threads are correct!) This is not of course saying anything against luxfer, their tanks are good!

HTH

Jon T

 

[Thomas Ivey]

Originally posted by turnerjd
I generally have a poor opinion of sherwood, in future, if you want GOOD quality tank valves may I suggest in order of preference,

Apeks - yess Apeks make more than just regs!
AP Valves (the 'Buddy' range of equipment)
MDE (England)

The americans on the board I am sure will be able to tell you the good / better American brands of tank valves.

In general the tank manufacturers sell tanks bare (no valve) and then the dive shop puts the valve in. Almost all valves go on any tank (provided the threads are correct!)

HTH

Jon T

If you are using a Luxfer tank with a Sherwood valve you are using two of the premium products in today’s scuba market. List below is info that you can perform on the tanks before you send them off to be inspected.
Ø Drain the tanks completely.
Ø Remove the valve.
Ø Inspect the o-ring gland in the tank; this is the recessed area where the o-ring sits. This gland must be smooth and very clean. If there is machining marks from manufacturing or corrosion in this area the tank will leak. Aluminum tanks under heavy use will corrode in this area.
Ø Next remove the o-ring, get rid of it, do it not reuse it.
Ø Source out a replacement o-ring, make sure it is the right size and hardness (90 shore) some scuba companies sell cheap o-rings and if there are too soft the tank will leak. If it is a Luxfer tank 99% chance that the thread is a ¾-14 NPSM (o-ring # AS568-214) most companies recognize the #214.
Ø When you buy the o-rings also purchase some silicone grease.
Ø Rub a very small on the o-ring.
Ø Inspect the valve where the o-ring sits, make sure the surface that mates up with the tank is flat. Some time people will use a wrench on a scuba valve and it distorts the material and cracks the chrome plating.
Ø Reinstall the o-ring.
Ø The o-ring gland and the bottom of the valve must sandwich together to make a seal. Any deformation of any mating surfaces will cause a leak.
Ø Reinstall the valve making sure that all threaded areas are clean.
Ø The valve should seat right on top of the tank. Nice and smooth
Ø Once the valves stops, and with the valve hand wheel in the off position lightly tap the hand wheel with soft hammer until the valve is tight. About three light taps should do it. Over tightening the valve will not help.
Ø Slowly refill the tank either in a fill bath or with soapy water and look for leaks.
Ø If the tank still leaks, you have done all you can on your own.

At three years, you are beyond any warranties that I know. Corrosion in the gland area is a common problem with aluminum tanks mostly seen in heavy use. Steel does perform much better in this area of exposure.

I hope I have been of some help.

ti