Adding a sinter filter to a pillar valve dip tube

[drcolyn]

I do recreational diving and the double valve-single tank solution is very economical on weight to me.
Doing shore entries dressed in a dry suit, 15 liter steel tank and DSLR setup is heavy enough.

The only problem I have is that I cannot find double pillar valves with double dip tubes anywhere and I might as well address the blocked dip tube problem while I am spending the money to convert my 3 tanks to double valve setups.

My local dive shop techie mentioned that some guys drill smaller holes on the side of the dip tubes just in case rust blocks the tip or they add a sintered brass filter at the tip of the dip tube.
Have anybody made/seen these modifications – I would appreciate some advice before I do something that cause and real problem where I did not have one before.

Regards
drcolyn

 

[captain]

An extremely remote problem in search of a solution.

 

[300bar]

Find a fillstation with dry air

I know Drager used to make diptubes with sinterfilters, but that was for firemen use (guess they didn't use dryair)

 

[redacted]

I can see a few extra holes in the dip tube but the filter makes no sense. I would rather any such crap that filter might catch be caught in my regulator sintered filter where I can see it and deal with the underlying problem.

 

[Akimbo]

Buy a small sintered bronze silencer with a threaded brass end. Braze a modified brass coupling or threaded tubing adapter to the dip tube. Make sure the maximum OD of both fittings fits thought the cylinder opening. Grind or sand the chrome off the dip tube end and you may have to drill the tube adapter for a snug fit before brazing.



It seems that each added measure we take against failures on open circuit Scuba systems protects against an increasingly lower probability of failure. There is no doubt that clogged dip tube and first stage filters have happened, especially using resort or charter boat tanks. Not to diminish captain’s comment in any way, but it does not matter how low the probability of that failure is if the solution is worth the price to you and provides sufficient peace of mind. However, this solution does not protect against a burst disk (if you require them on Scuba valves in South Africa) or extruded valve O-ring failure.

My main caution is to make sure you inspect or prophylactically replace the filter/silencer cone frequently or your precaution may become the source of the problem. Google “sintered bronze silencers” to find a local source. You can get them in stainless, but bronze is less expensive and the appearance of corrosion is an indicator that you need to change them more often and find a drier source of air fills.

 

[captain]

If you took a piece of debris of sufficent size to completely plug the dip tube and placed it in the tank how many millions or billions of times would you have to invert the tank before the debris would end up in the tube. Dip tubes are to prevent water, which shouldn't be in the tank to begin with and debris, mostly flaky rust, which also shouldn't be in the tank, from getting in the valve if the tank were inverted with no dip tube.
Being these are his own tanks not rental tanks effort would be better spent maintaining clean tanks.

You can pinch the open end of the dip tube closed and drill two holes just below the pinched end. I have a couple of vintage valves that came that way. That way you would have to be twice as unlucky to win the billion to one loto that both holes would plug at the same time.

 

[Akimbo]

Given that I have only heard of two instances where particles from a cylinder have blocked flow in 50 years, captain's estimate of odds may be pretty accurate.

I have had only one true CESA from that depth range (80 ft). It happened when my dip tube became clogged with debris from inside the tank and stopped all delivery of air through the valve...

…I have seen one instance where a first stage filter was fully plugged during the first dive due to some very sloppy maintenance. How well do you trust the whole air source system and the people operating it?

A word of caution: If the source of contamination is from the compressor system and not internal cylinder corrosion, the dip-tube filter would collect all or most of it. In that case all the crud would be sucked into your regulator almost immediately… or a maybe wait long enough for you to reach bottom.

I have heard about a lot more burst disk and valve extrusion failures in that period. Of course a full backup for the sixth backup is essential in case the seventh backup fails. Are we still having fun?

 

[captain]

I think in Dr Bill's case it was constant wet air fills form a dive boat onboard compressor that lead a lot of rust. I believe the end result was the tank had to be scrapped.
What would be worse a plugged sintered filter on the reg or on the dip tube, kind of 6 of one and half a dozen of the other.

 

[drcolyn]

Hi All

Thanks for sharing all the good advice and experience.

RE dry air - I used only one dive shop in Cape Town for the last year rather than local commercial dive operations as before – that’s the reason for having three tanks now.
I always have my tanks visually inspected annually as per SA law but I will have peek for rust myself as one tank is due for a visual now.
RE blown burst discs – not in use in SA luckily.
RE blown valve o-rings – the LDS techie assured me that Faber M25 necks with the recess is the least prone to give problems.

Thanks for that sinter filter tips Akimbo – exactly what I thought to do.
Just one question – will the annual visual inspection be frequent enough to detect a corroded sinter filter or is this trail and error. I cannot do half yearly visuals myself as SA law requires any tank below 20 bar to get a formal visual inspection before it may be filled again.
Regards

 

[knowone]

I would think about spending your money
making a transfill whip, and then you can
peek about whenever you fill like peeking