Filter modification assistance

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Thanks for all the info pescador, theres quite a lot there I didnt know and need to be aware of, great info.

I called the distributor of the dessicant who tells me it is "molecular sieve" but it dont have a brand name to identify it and its sold in a vacuumed sealed bag - do this sound right to you?

I suppose I can just reseal it into a bucket, but I am going to look a bit further as well. I would like to get a molecular sieve with some kind of brand name that I can identify initially if possible.

I got the filter dropped off at the machine shop today for milling to size but work (go figure) got in the way of my project and I didnt have time to get it back or re-check the filter flow direction.:depressed:

Ill try again tomorrow.

 

[pescador775]

The brand is not important because distributors just slap on a name to a product that they buy in bulk from a no name factory, but the specifications are important. The sealed bag is OK for a couple months but it should be transferred into plastic jugs or metal cans with screw on tops. As mentioned above, the type of molecular sieve used for breathing air compressors is (preferably) synthetic zeolite(sodium silicate), 13X (10 Angstrom). If it is synthetic and "13X" and the particle size is about 2-3 mm it is usable.

About work, first things first. Since you are a heavy user of filter cartridges this is certainly a worthwhile project. If it takes up a bit more time to figure it all out, doan worrry aboud it, as they say in Brooklyn.

 

[rcontrera]

One additional note. If your filter tower is one that has an auto drain on it (most of the Coltri machines do this), it is best to go with the 3-5 MM beads rather than the 1/16" pellet or the 1.5-2.5 mm beads.

The only reason for this is that when fully saturated and subjected to radical air flow changes (like during blowdown), the beads can self destruct and "ooze" through or around the filter pads into the blowdown system ... causing an eventual leaking of the blowdown valve. We have seen this more with the tiny beads than with the large ones.

If you don't have a blowdown off your filter tower, ignore this post.

 

[pescador775]

Thanks, Ray, good point. Did you see that, Widget? Get something with a 4 mm size or thereabouts. Don't go too small. Molecular sieve is formed into spheres or cylinders. I have no personal preference.

I called the vendor of the generic "window pane" desiccant and the product is basically powder. Bad luck because I would like to find a source of cheap desiccant also.

About zeolite, a naturally occurring mineral. Desiccant is made from mined zeolite but I hear that the synthetic version is higher quality.

 

[pescador775]

The following was written to a British blog in 2006 by a person who regularly contributes to SB. I feel that this may be of interest:

Damien. There is nothing wrong in packing your own filter cartridges just a few things you need to be aware of as well as the sales pitch.

1.The original Bauer metal cartridge is a thin wall anodised aluminium tube with a very thin protective oxide film. This is only good for around six refills before the wet sieve will rot through the original thin wall aluminium cartridge.
2. Also the aluminium cartridge tube is crimped to the base and the lid so rendering it a PITA to adapt into a repack
3.An alternative approach is a stainless steel filter cartridge for indefinite life. Modify the cap (two small screws through the cartridge wall) and spring load the chemical pack with a stainless spring pushing a plastic wad packer.
4.The drying filter material used by Bauer is a standard industrial 13X grade Molecular sieve with a “binder” volume of around 20% by weight This binder chemical is incidentally carcinogenic thus the silicate warning on the cartridge regarding disposal in a land fill site.
5.Better still would be a non bound 13X high grade sieve that at equal weight would allow 20% more water uptake as it doesn’t contain this inert clay silicate binder. Just a little more expensive.
6.The chemical life quoted at six months is only a sales pitch, based on what? Kept in a damp cellar wrapped in a paper bag no doubt. Small chemical batches can be easily stored in metal tins with no problem in any conditions.
7.Do the same for the activated charcoal or activated carbon as it is known now. Make sure it’s made from coconut husks 207C would be a good grade for diving air purity.
8.Pricing Charcoal is around £5.50 per kilo, Moly Sieve standard grade 13X £4.00/kg and for the non carcinogenic 13X type £11.00/kilo.
9.Bulk is a 5ltr drum contains 4kg or Moly sieve or 3.2 kg of activated carbon.
10.Use a visual air purity monitor £50.00 with the small water vapour indicator card that turns from dry blue to pink when wet.
11.Bauer use a soft sponge disposable pad in the throw away cartridges, use a high density polyester pad £2.00 clean and re use the upper pad.
12.Note the Bauer filter shell has a vent line in the base in case you forget to fit a cartridge hence the need for two o-rings in the repack cartridge.
13.Then monitor the actual filter life between your new repack as above and the old original throw away cartridge. The repack will last longer and cost about £8.00 per fill. Your call.

 

[pescador775]

Kaolin clay (China clay) is a typical binder used to form beads. This clay may contain about 2% quartz which, under very special circumstances of prolonged occupational exposure to high concentrations of quartz dust, may cause silicosis or cancer. However, studies of workers in the production of this clay have shown no unusual incidence of cancer. IMO, there is absolutely no relevance to use in divers compressor filtration systems.

 

[iain/hsm]

Hey talk about being careful with what you say!! I guess it was me who wrote all that about carcinogenic binders in the chemical, however to explain myself.

At the time of that post we were developing a high pressure filter plant for a medical hyperbaric chamber so the emphasis was on purity, what with all the liability issues and possible legal actions we felt that removing the binder (the carcinogenic agent) was the way to go. That way we could demonstrate fully that we were providing pure gas for breathing but without any possible legal or medical complication in using carcinogenic agents in the air purity process.

There were also many other indirect advantages, for example another was in the area of cost over performance.

1. The increase in cost for the chemical from £4.00/kg ($8) to £11.00 /kg ($22) was largely balanced out by the increase in filter life.
2. Also reduction of inert clay binder alone increased the filter life output depending on the type and percentage of clay binder used, by another 20% to 30%

So to be fair it was not entirely the clay binder quartz issue that was in question it was just a factor in the decision of chemical quality chosen.

Another interesting project we are doing at the moment is that of filter life cycle testing using American, British and German throwaway cartridges,
In the UK we test by spectrographic analysis at <25Mg cuM3, and to make the test fully independent transparent and valid for scuba diving we are using the same compressor at our local dive shop (ADM Diving Leicester) using the same filter shells and the same back pressure regulator setting. They compress the air as normal using each brand of throwaway cartridge twice to get an average filter life. Then the spent cartridge is cut open and only the filter chemical is replaced.

That way we can test with the same dwell time, diameter, volume, jet size, etc before making up the “ideal” filter package. By using the same old cartridge again and again we keep the results valid with the new medical grade chemical or any other chemical we care to test. I will not discuss each brand tested but to disclose the worst average result was 29 hours running for the filter shell. The best result was better than expected when replaced with the medical grade sieve the filter ran for 250 hours and the filter was changed for the second time on 30/08/08 after running 298 hours.

This testing is still a work in progress but other technical features that are valid are:
1. The compressor is a modified 155 l/min (5.5 cfm) oil free oil less block, running at 1500rpm from a 380v 4Kw 5.5HP TEFV motor.
2. The banks are 50 liter water capacity at 350 barg (5000psig)
3. Even without any chemical filters the compressor produces on its own breathable oil free air to BS4001

I should also state that an oil lubricated compressor will not achieve anything like the same running hours. Due in part to the increased heat loadings interstage with an oil lubricated compressor and the contamination of the synthetic zeolite chemical, a 13X angstrom matrix at the molecular level as the oil particulate causes what is in effect an oil film coating over the chemical “ball” in effect blocking off its ability to adsorb water vapour.

Now my crucial point is to encourage the use of self pack or refillable cartridges, and at the same time offer a valid option in the choice of chemical used, clearly with a hope to demonstrate also that repacking cartridges can be done safely and effectively.

However already I am encouraged by some critics are calling it “counterfeit” but the lack of performance from some of these disposable throw away cartridges and the use of oddball 3rd rate industrial chemical cocktails could be what is really in question.

The one critical question I have with our throw away filter systems used throughout the scuba diving industry is that as there is little profit in using a good chemical or that which lasts a long time, to some degree companies may be deliberately opting to use poorer quality industrial chemicals simply to minimize filter life and to maximize change out profit? I don’t yet know the full answers, but I guess we soon will.
I on the other hand could not possibly comment!!! Iain Middlebrook

 

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Hey, some great info here, its amazing the knowledge of folk here on the board.

Whats that saying "if we put our heads together, anythings possible" - certainly applies I think.

Anyway, I have been diving for the last two days - work related - and while we were inspecting a ship hull we looked down and there 3 metres below us was a Tiger shark, (maybe 4 metres in length -(12ft?) - I snapped off two or three shots as I had a camera, no flash but still good enough, its not that common to see these apex predators around working ships so I though it was quite notable - should I submit em in the photo section? - would anyone be interested to see it?

Anyway, sorry about the diversion , - friday I am going to see the distributor for the molecular sieve and I have all the info on size to show him - thanks fellas.

The cartridge fits perfectly now after its machining, I have got the activated charcoal samples today so on friday I will get the dessicant and we can start up production.

 

[pescador775]

Thanks, Iain; very meaty stuff which will likely be of interest to many, including some sharks, I guess. Keep a camera ready, heh.

 

[iain/hsm]

Ray, your point is important, critical even and should not be ignored, it also adds to my original point another reason why clay binders should not be used in scuba diving filters. With or without auto drains the problem is the same its just that with auto drains they increase the frequency of the problem.

When a filter is adsorbing water the dry filter &#8220;front&#8221; travels up through the chemical bed as each bead of chemical does its job of adsorbing (in the case of molecular sieve the water content) as the gas flows around and or through the chemical bed.

Too much gas flowing around the beads is called &#8220;channeling&#8221; and too much flowing through the bed is called an aggressive &#8220;dwell time&#8221;

However as the process gas travels along the filter bed length two other reactions occur:

1. The first is that of the wet gas on contact with the fresh dry molecular sieve creates a huge exothermic reaction front and this is a major cause at high pressure air plasma fires within the chemical. Typical temperatures are high enough to easily burn off the anodizing from any aluminium component. However under normal operating conditions the flow of air does cool the reaction front.
2. The use of nitrox or oxygen enriched air mixtures through the filter chemical also increases these exothermic events.
3. The 3rd major problem is at the &#8220;spent&#8221; end of the filter when the wet liquid water condensate in old or poorly drained filters reacts with the clay in the chemical making in the worst case a solid clay &#8220;slug&#8221;. Now as the air flow is effectively blocked and air at 207barg (3000psig) is a good pneumatic piston (think air gun) this will either crack the filter cartridge or if a stainless cartridge is used it can &#8220;swage&#8221; or balloon out the cartridge metal tube and elongate the cap thread holes it is so powerful.
4. Massive pressure drops during draining and auto bleeds turn any moisture within the filter chemical into an expanded ice block, It is this expansion of the ice that caused the filter material to crack up and brake up into a powder slurry, dissimilar binders like clay within the zeolite also are the "fault lines" for this. Remove one componant (the clay) and you reduce your problem.

IMHO if I may make the comment on the specific problem with the Coltri filters it is that there filter diameters are too small for the chemical bead size. Out of interest Ray can you tell me the internal diameter of the Coltri cartridge and its chemical length?

This will get us into a little known event called the &#8220;Kepler&#8221; effect simply put the relationship between the filter packing and the contact area of the filter wall. Although Kepler was more interested in how many apples you could fit into a barrel and is better known for his work in physics with Keplars 3rd law P^2 = a^3 / mt of motion between planets, his work on the time period squared being directly proportional to the distance cubed.

The one and one only reason why most scuba filters are between 90 to 100mm in diameter is to allow for a chemical cartridge of between 60 to 70mm internal diameter.

It is this relationship between flow, dwell time, pressure drop, and the space between the contact areas of the chemical against the contact area of the filter wall that Johannes Kepler born 1571 died 1630 understood so well and that Coltri doesn't. LOL Iain Middlebrook.