DIY Compressor Filter and Dryer designs

[maniago]

Scuba Compressor or SCBA Air Fiter Canister 5000 PSI Uses Std Filters | eBay

This is what we use. We use pad retainers, synthetic felts pads, and then hand pack them.

They hold about a quart or so of media.

I'd probably do:

50% MS13X
10% Hop
40% AC

You want to plumb from the bottom up. The 15 micron filter at the end is good in case some of the media weasels past the felt pads.

I suggest mixing some drierite crystals in with the MS13X. It'll give you a good idea of your service interval for your filter.

Ah nice, now were talking a bit more reasonable pricing. Those $800 stacks minus any filter cartridge are flat ridiculous.

 

[swamp diver]

Here is some data to give you an idea of what other companies are doing. The percentage is based on inches of the total cartridge height excluding the pad height. The order will be MS/AC/catalyst with airflow starting in the MS bed.

Bauer 86/10/4
Lawrence Factor 79/15/6
Mako 73/20/7
Irwin Air 70/27/3

From a typical 27 inch tower you'll find the following pad heights:

Bauer 3.5 inches (foam)
LF 2.0 inches (polyester)
Irwin Air 1.6 inches (polyester)

I've always been a big fan of large AC beds given the VOCs which come off the compressor oil as well as ones in the ambient air. These compounds are the most narcotic, especially the halogenated and aromatic ones, so if you think there is any possibility of vapors from these compounds being present in the ambient air I'd go with at least 20 percent AC. On the other hand with the Rix you don't have to worry about lube oil VOCs.

Something like 65/30/5 percentage might do the trick. Be careful when handling the MS as you don't want to breath in the zeolite dust.

If you are going to add a particulate filter I'd go with the LF 2 micron filter which will at least get the fine particulate out of the airstream. It is the fine and ultrafine particulate which is most biologically active. Your intake filter should filter out anything less than 10 to 20 microns from the ambient air depending on brand.
LAWRENCE FACTOR® – Cartridge Holders

 

[maniago]

On the other hand with the Rix you don't have to worry about lube oil VOCs.

Ok so help me out with this guys. If the Rix has no oil, why do I need any carbon at all? Wouldn't it make more sense just to load up on more MS, leaving the cat as is noted above?

 

[swamp diver]

Ah nice, now were talking a bit more reasonable pricing. Those $800 stacks minus any filter cartridge are flat ridiculous.

You might want to consider the life expectancy of any used pressure vessel you are going to buy on eBay. If there was no PM valve and it was cycling from 0 psi to system pressure the service life (load cycles) will be quite short. If you don't know the history most manufacturers are now saying 15 years maximum for aluminum appliances unless you get them hydroed. There have been many separator failures and I've see a few filter failures of the older aluminum type.

You might want to review your house insurance and see what it says about damage caused by a pressure vessel failure.
http://jordair.ca/pdf/SAFETY-WARNING-Alloy-Filters-Feb06-2003.pdf
http://www.bauer-kompressoren.de/pd...en/serviceunterlagen/lastzyklen-tabelle_e.pdf

---------- Post added February 15th, 2014 at 08:37 PM ----------

Ok so help me out with this guys. If the Rix has no oil, why do I need any carbon at all? Wouldn't it make more sense just to load up on more MS, leaving the cat as is noted above?

You mentioned you are going to run the compressor in your garage. If you don't run a remote intake to the outdoors then garages are typically full of VOCs. If you have brake or carb cleaner in your garage you have a source of methylene chloride and trichloroethylene which the maximum exposure level for air diving is only 5 ppm and 1 ppm respectively. Even if your intake is outdoors you don't know what your neighbors are doing with paints, glues, etc.

If you are pretty sure your risk for ambient air VOCs is quite low then you could drop the AC bed down to say 20 percent but personally I would not go much below that. While excessive water vapor might cause a free flow or corrode your equipment a tank containing a few ppm of TCE might end your day depending on depth and duration of exposure.

 

[maniago]

While excessive water vapor might cause a free flow or corrode your equipment a tank containing a few ppm of TCE might end your day depending on depth and duration of exposure.

No friggin way dude - so hitting the bong while I'm filling my tanks is gonna be like a total downer then? (just kidding)

Point above well taken. This stuff can really make you wonder what the heck we're doing trying to breath underwater...or more importantly the blind faith one has in LDS compressor jockeys...

 

[swamp diver]

Most dive shop compressor operators have little knowledge as to what can go wrong with a compressor and the resultant air contamination. Fire service guys are much better trained and the equipment is generally up to date and maintained.

Here have a look at this to see what a little bit of crude oil smeared on your dry suit can do with regard to narcosis in the diving bell. The guy was asked to put on his full face mask as he was acting odd after returning to the bell. Many of the same vapors exist in the older mineral oils used in dive compressors hence the importance of large AC beds.
Diving Bell atmosphere protection with Analox Hyper Gas - YouTube

We all should all really be using RIX compressors in the dive business given the unforgiving environment we dive in, but as you found out the cost of purchase and maintaining a RIX is very high. All hospital compressors must now be oil-free or oil-less and that is for compressed air used at only one atmosphere.

 

[maniago]

Dang! The guy with the mask look like hes just rolling it around in his hands like a ball. I've been hypoxic on a chamber ride and when I came to, I was totally confused. Completely lost 5 mins of my life in what was to me, a blink of an eye.

 

[swamp diver]

You can see the difference in the various pads used in the filters here. The ones on the left were taken from an unused LF 27 inch cartridge and on the right from an used Bauer 27 inch cartridge where the charcoal dust can be seen in the filter. The filter cut point on the Bauer foam ones is about 20 microns if I recall but that doesn't take into account electrostatic forces which can trap much smaller particulates.

 

[maniago]

You can see the difference in the various pads used in the filters here. The ones on the left were taken from an unused LF 27 inch cartridge and on the right from an used Bauer 27 inch cartridge where the charcoal dust can be seen in the filter. The filter cut point on the Bauer foam ones is about 20 microns if I recall but that doesn't take into account electrostatic forces which can trap much smaller particulates.
View attachment 177815

No doubt that's impressive, but the question to be asked is it over designed? I don't need a Porsche, just a chevy that won't fail me. In my case, is a 27" stack really required for an (at best) 5cfm pumper? What really is the size I should be looking for that does the job for what I need?

 

[swamp diver]

No doubt that's impressive, but the question to be asked is it over designed? I don't need a Porsche, just a chevy that won't fail me. In my case, is a 27" stack really required for an (at best) 5cfm pumper? What really is the size I should be looking for that does the job for what I need?

It depends on how much you plan to pump over the year. You'll find that if you change out your media just as the 20 percent sector is changing to pink in order to protect your catalyst bed the filter processing capacity is much less than what you think. Plus if we continue to have these hot humid summers the correction factor to the processing capacity when the filter inlet temperature is 32 C or higher is about 0.20. In other words a filter that is rated for 100 hours at 50 F will only be good for 20 hours at 90 F.

If it is just for personal use during the summer with a 5 cfm compressor you can probably get away with an 18 inch tower. I think Rjack has the smaller Bauer P21 filter on his 4 cfm compressor filled with MS prior to his larger tower and in the summer if I recall he gets about 9 hours only before the MS must be changed out.