Putting a Filter after the cascade?

[JBRES1]

I am in the middle of setting up my home/office compressor with storage bank, and secondary filtration. Today I was o2 cleaning the cascade bottles, and I started to think about where I should put the second filter. In my original plan I was going to put the filter at the start of the system , but now I am thinking about putting it after the cascade bottles just before the fill whips.
Is there any problem with my plan ? Does anybody else have their system set up this way ?

Thanks, Jim Breslin

 

[CraigAClark]

Does your secondary filtration have a flow restrictor to increase the dwell time? If that is the case, it should be downstream from the cascade. I am assuming that the air going into the cascade is Grade "E" or better.

If you are feeding air directly from an oil lubricated compressor's filtration into the storage bottles, why would you O2 clean them?

Craig

 

[PhilEllis]

I am in the middle of setting up my home/office compressor with storage bank, and secondary filtration. Today I was o2 cleaning the cascade bottles, and I started to think about where I should put the second filter. In my original plan I was going to put the filter at the start of the system , but now I am thinking about putting it after the cascade bottles just before the fill whips.
Is there any problem with my plan ? Does anybody else have their system set up this way ?

Thanks, Jim Breslin

HI Jim. If your "second" filter is a hyper filter (attempting to produce E grade air with J grade hydrocarbons - modified J) then I think it should be placed so that it isolates and cleans only the air that will be used for oxygen service. When using the compressor to fill standard air, it should not flow throught the hyper filter. Those cartridges are expensive and there is no sense cleaning the air when it isn't necessary.

I assume you have a TWO filter stack prior to moving the air into your banks. The first cartridge should be sieve only and the second cartridge should be sieve, carbon, and hopcalite. I think this is considered the state-of-the-art combination for breathing air compressors these days. The hyper filter should be IN ADDITION to these two.

As to cleaning your bank bottles, congratulations. I think that is absolutely necessary for a state-of-the-art system for gas mixing.

Phil Ellis

 

[JBRES1]

Phil and Craig,
Thank you for responding.
So far all I have is an Airetex W31 compressor, 6 storage bottles, alot of valves ,fittings and SS tube. I still need to purchase the filter system for the setup.

Let me eqplain what I want to end up with. My plan is to have the cascade system set up and filled with only Nitrox (either a 32 or 36)

I will be using the OXY HACKER gas blender design from the book, and running it into the storage banks. My first plan was to filter the air as it came from the compressor, thru the compressor filter, past the visual indicators for moisture and CO, into a second filter, then into the cascade system.

As for O2 cleaning the storage bottles, I wanted to start off with everything being as clean as I can make it. With the bottles being as clean as I could get them now I need to clean all of the SS tube, fittings and valves to make sure they are as clean as the bottles.

As for cleaning the cascade and tube system for nitrox may be a little over the top, but I would rather be safe rather than sorry.

Any recomendations for a filter ? I was looking at the L F filters .

Thanks, Jim Breslin

 

[pescador775]

Jim, your plans include pumping NITROX through an oil lubricated compressor and then, following the planned flow of gas as you explained it, you are concerned about eliminating any trace of oil downstream, for safety. Is that correct?

The maximum hazard occurs during the drama of pumping the gas through a hot compressor where everything bathed in oil vapor. Yet, this is a generally non-hazardous procedure within the known limits of safe O2 concentration. What makes you believe that any storage or flow which occurs downstream of the compressor will be made safer by rigorous cleaning? IMO, in this case which is typical, the hyper filter is more hype than filter.

If you are instead covertly planning on jamming cylinders which are already partially filled with oxygen, then the hyper filter might be a good idea although it should be mentioned that the cascade bottles will act as condensers removing any residual oil which in any case will be minute.

 

[Doc Harry]

Jim, your plans include pumping NITROX through an oil lubricated compressor and then, following the planned flow of gas as you explained it, you are concerned about eliminating any trace of oil downstream, for safety. Is that correct?

Don't mean to hijack the thread, but I too am about to set up a system similar to Jim's, with an Alkin W31 and a Nitrox stik. Are you saying the Alkin W31 is not the compressor to use for Nitrox continuous blending?

 

[pescador775]

No, I'm not saying that. The point is that hyper filtering is not required when filling cylinders with <40% oxygen content NITROX mix.

Don't mean to hijack the thread, but I too am about to set up a system similar to Jim's, with an Alkin W31 and a Nitrox stik. Are you saying the Alkin W31 is not the compressor to use for Nitrox continuous blending?

 

[rjack321]

I use the stock Alkins filter and a secondary 18" tower and it produces air suitable for partial pressure blending. It not specifically a hyper filter, but achieves the same result.

I would definately not put any filter after the bank bottles. Unless you have a flow restrictor you may blow the guts of the filter into you tanks (a disaster). And if you are spending all the effort to clean your cascade bottles why put less than OCA into them? Any hydrocarbons will be condensing in those tanks negating the cleaning.

The second issue is with the Alkins P0 primary filter. Quite simply its not that reliable. Its very small and goes from pumping fairly clean and dry air to pumping pretty wet gas in short order (~1/2hr). In my climate I get 9hrs out of the filter media in summer and 25hrs in winter. The table in the manual is WRONG. Its not too far off if you realize that someone used compressor inlet temp instead of filter inlet temp when generating the numbers. So add 15F to the temps shown and the hrs approxiamtely work out.

So all in all, there's a good chance you will delay in changing the primary filter someday (inadvertently) and pump at best pump wet gas into your storage banks, at worst oily gas.

Personally I only PP blend EAN50 at this time. I continuous blend EAN32, 21/35, 18/45 and have on occasion put 100% He through my W31. I have about 150hrs of continuous blending time on it. I have 2600cf (I think) of 32% stored and filled by CB. All the gas goes through both filters all the time.

 

[JBRES1]

Pescador775,
Yes the reason for the second filter is for safety, and better air/nitrox.
The reason I was thinking about a filter at the end was (1) to insure the air was as clean as I could make it at a reasonalbe cost, (2) I had seen my LDS's fill system and they have a filter stack just before the fill station.


Doc Harry ,
Hijack away as long as I can get help with my system and some information .

Rjack,
What filter did you use as your second, and what do you fill the stock filter with on the W31.

Thanks to all in advance,
Jim Breslin

 

[rjack321]

Its a standard small Lawrence Factor chamber with a triplex (13x,monoxycon,AC) filter. Priority valve immediately after (set to about 2000psi).

I fill the primary chamber on the Alkins with 13x and AC. It takes about 4:1 (13x to AC). You don't want to fill the primary filter with just 13x. Then you end up being limited by the AC in your secondary filter and there's no good way to know if that is saturated with vapors. Better to be water limited and then be able to exchange your filters in a timely manner.

I end up changing my secondary filter every ~7-8 months. Costs me about $45. Based on may usage that's about the maximum processing capacity (13,000cf). The little indicator strips have never even started to turn, but of course I have removed the vast bulk of the water using the primary filter anyway.

If you have a huge filtering capacity you'll probably just want/need to change the filters annually (long before they hit their capacity) anyway. Lord knows what kinda mold might grow in there given enough time and moisture.

My vote is to:
1) put all your filters before any banks/tanks
2) change the primary filter regularly based on RH >20%. Use the TexasTechnologies 10/20/30 RH sensors
3) Chuck the CO "dot" sensors (which are often dried out and even when perfect only change color at 50ppm which is way way too high).
4) get yourself a real CO monitor
5) use a smaller secondary tower and change that based on time, not moisture since its not getting much of a RH load
6) use a triplex filter in the secondary chamber
7) CB everything you can
8) Only partial pressure deco mixes >40%
9) Get a thermometer and log your hours and pumping temps

This gives you the best bang for the buck and no worries about whether OCA has or hasn't been put into which tanks etc. Also gives you redundancy if you fail to change the primary exactly on time or moisture load. Probably a better setup than most dive shops and will give you 100% confidence that you aren't breathing something you shouldn't be.