Compressor Filtration

[BillZ]

My winter project this year is to build a continuous blend nitrox fill station in my garage. I picked up a used circa 1976 Bauer K14 compressor last month and I'm now going through the process of figuring out the filtration that I will need to bring it up to todays standards. Although I won't be partial pressure blending 02, my goal is to get as close to OCA as possible without breaking the bank. The fill station will be used to pump about 10,000 - 12,000 CF of nitrox a year.

The compressor is rated at 5cfm/3200 psi. It currently has two moisture separators- one between the second and 3rd stage and another after the third stage. It has a small (approx. 12" tall X 2' DIA) hand packed filter stack after the second moisture separator.

Here's my rough plan:
Leave the two moisture separators on the compressor but remove the current filter stack and reuse it in the "filtration panel" for desiccant. I'd then add a 32" filter tower and moisture eye to the panel.

So, running it through my head, the filtration panel would look something like this:

Check valve > desiccant filter (old filter) > moisture eye > 32" filter tower > gage > pressure relief valve > priority valve

So, for you home brewers out there - Does this look about right?

[kdupreez]

I'd put the moisture eye after the tower, also add a bleeder before the priority valve / pressure maintenance valve (PMV), else you will be stuck with 2000psi in the towers and no way to bleed them.

In my system the check valve is also down stream of the PMV since my PMV is not one way.

also - I'd add a check valve after the final separator if there is not one already because if drain moisture, it will back flow your gas from your filter stack back into the separators.

Below is a pic of what I have AFTER my filters.. the Gauge and Bleeder sits to the left (upstream) of this pic..

Oh - and if you need Aqua Environment parts, I can probably get them for you at a great deal. (drop me a pm)
http://www.aquaenvironmentinc.com

And when you get to the Nitrox continuous mixing, drop me a note. I built my own mixing stick for less than $50 in parts and also added auto shut-off for the Oxygen via a solenoid connected to magnetic starter and pressure sensor.

[BillZ]

Thanks Kooos! That makes sense and covers a few scenarios that I hadn't thought about.

Oh - and if you need Aqua Environment parts, I can probably get them for you at a great deal. (drop me a pm)
http://www.aquaenvironmentinc.com

Thanks! I'll definitely take you up on your offer. I didn't realize how expensive all of the valves etc. were before I started the project.

And when you get to the Nitrox continuous mixing, drop me a note. I built my own mixing stick for less than $50 in parts and also added auto shut-off for the Oxygen via a solenoid connected to magnetic starter and pressure sensor.

I never though about adding a auto shut-off for the O2 - My assumption was that it would cost a fortune. I'll definitely get in touch when I start putting the stick together.

A few quick questions ...
What filtration are you using?
Snoqualmie is pretty close to where I live - Where are you sourcing your gas?
Are you continuously blending HE or just O2?

Thanks again for the help Koos! I probably will start building my station in December so I'll touch base with you when the project gets closer to getting off the ground.

[kdupreez]

for O2 shutoff, the solenoid is like $100 and you wire it straight into the magnetic starter.. a auto shutoff at max pressure on the compressor is around $50 and you can combine that with the o2 shutoff too.

I use Lawrence Factor pre-packed filters and have 2 towers. I get about 15-20hrs out of one and about 60hrs out of the other, so I order one big one and 3 small ones at a time.. I can also get you the filters at around 15% less retail, just let me know. I only do about 60-80 hours per year on my 12cfm, so I very rarely buy fitlers, and self-packing is a PITA enough to just buy pre-packed.

I get gas from Central Welding in Renton delivered and I continuous blend nitrox and trimix.

for sure touch base, I'm like 20min away from you, so stop on by for coffee or beer and I'll give you the low down.

[rcontrera]

Koos

If your compressor is 12 CFM, why did you choose the economy PMV since it is only rated for 10 CFM?

[kdupreez]

I have one of the bigger AE model 211's with 2 outputs that's rated at 50scfm, the plumbing has just not been updated since I got my new MCH16 mini tec last year.

it's been working fine, so I haven't felt like spending the time ripping the plumbing apart for a ~1 cfm difference.

there's no back pressure creep, so I figured its ok until I have the time again.

[CaptnJack]

Your sequence will work. Its not that hard to produce OCA actually and 2 filters will get the job done.

But what will you use to gauge when to change the 32" tower? I'm afraid you will continue to change out the pre-filter which will extend the life of the 32x in the 32" tower (essentially indefinitely) but at some point the AC bed in the 32" tower will be maxed out.

[BillZ]

for O2 shutoff, the solenoid is like $100 and you wire it straight into the magnetic starter.. a auto shutoff at max pressure on the compressor is around $50 and you can combine that with the o2 shutoff too.

I use Lawrence Factor pre-packed filters and have 2 towers. I get about 15-20hrs out of one and about 60hrs out of the other, so I order one big one and 3 small ones at a time.. I can also get you the filters at around 15% less retail, just let me know. I only do about 60-80 hours per year on my 12cfm, so I very rarely buy fitlers, and self-packing is a PITA enough to just buy pre-packed.

I get gas from Central Welding in Renton delivered and I continuous blend nitrox and trimix.

for sure touch base, I'm like 20min away from you, so stop on by for coffee or beer and I'll give you the low down.

Thanks again Koos - I'm headed to warmer water next week but would love to by you the beverage of your choice and pick your brain. I'll PM you early next month.

[BillZ]

Your sequence will work. Its not that hard to produce OCA actually and 2 filters will get the job done.

But what will you use to gauge when to change the 32" tower? I'm afraid you will continue to change out the pre-filter which will extend the life of the 32x in the 32" tower (essentially indefinitely) but at some point the AC bed in the 32" tower will be maxed out.

Good question Richard - One that I hadn't really thought through. I know the pre-packed filter has a 6 month lifespan once opened and I assumed a rating for volume of gas. If I hand packed the tower I'm not sure what the change cycle would be.

Any suggestions?

[CaptnJack]

Are you hand packing either the "prefilter" or the 32" tower?

[BillZ]

Are you hand packing either the "prefilter" or the 32" tower?

The prefilter would be hand packed with 13X. I'm not sure yet on the 32' tower - I'm still in the process of finding one.

[CaptnJack]

I would not pack the prefilter entirely with 13x. I would pack it with 2/3rds 13x and 1/3rd AC. Then change it when the humidity indicator shows 20%. Use a triplex cartridge in the 32" tower. Change the 32" tower when its reached its rated volume capacity. Hours x 60 x cfm of compressor.

This way you 1) will never saturate the 13x bed of the 32" tower, 2) always have dry AC and hopcalite in the 32' tower.

13x really only removes water. Gaseous comtaminants and CO need to be eliminated by the AC bed and the hopcalite. You can't get either the AC bed or the hopcalite wet at all (>20% RH) or they start to fail. You can monitor for water via the RH indicators, and for CO (should be 0 or at most 1ppm). But you can't practically monitor for volatile hydrocarbons. So to ensure that they are fully captured by the AC bed you need to deliver dry gas to the AC and avoid the chance that the AC bed becomes overloaded. The common way to overload an AC bed is to use a prefilter and fail to change the secondary tower often enough. Many commercial filters actually have fairly skimpy AC beds too. A prefilter of just 13x keeps the second tower from getting wet, but the lengthened periods of use overloads the AC bed - your only AC bed. This is the reason to add some AC to the prefilter, so that the prefilter not only extends the life of the 32" tower's 13x but its AC as well. The hopcalite, being a catalyst doesn't wear out, as long as its kept very dry.

Even if you don't hit the rated volume of the 32" tower (should be about 12,000 cf of gas) change that filter after a year.

[BillZ]

I would not pack the prefilter entirely with 13x. I would pack it with 2/3rds 13x and 1/3rd AC. Then change it when the humidity indicator shows 20%. Use a triplex cartridge in the 32" tower. Change the 32" tower when its reached its rated volume capacity. Hours x 60 x cfm of compressor.

This way you 1) will never saturate the 13x bed of the 32" tower, 2) always have dry AC and hopcalite in the 32' tower.

13x really only removes water. Gaseous comtaminants and CO need to be eliminated by the AC bed and the hopcalite. You can't get either the AC bed or the hopcalite wet at all (>20% RH) or they start to fail. You can monitor for water via the RH indicators, and for CO (should be 0 or at most 1ppm). But you can't practically monitor for volatile hydrocarbons. So to ensure that they are fully captured by the AC bed you need to deliver dry gas to the AC and avoid the chance that the AC bed becomes overloaded. The common way to overload an AC bed is to use a prefilter and fail to change the secondary tower often enough. Many commercial filters actually have fairly skimpy AC beds too. A prefilter of just 13x keeps the second tower from getting wet, but the lengthened periods of use overloads the AC bed - your only AC bed. This is the reason to add some AC to the prefilter, so that the prefilter not only extends the life of the 32" tower's 13x but its AC as well. The hopcalite, being a catalyst doesn't wear out, as long as its kept very dry.

Even if you don't hit the rated volume of the 32" tower (should be about 12,000 cf of gas) change that filter after a year.

Thanks Richard, that sounds logical and I'll use this plan once I get my fill station up and running. It's amazing how little filtration they used back when the compressor was built - Just the one small filter can packed with AC ( about a cup and a half) changed every 10 hours. I'm surprised there weren't more accidents.

[CaptnJack]

Thanks Richard, that sounds logical and I'll use this plan once I get my fill station up and running. It's amazing how little filtration they used back when the compressor was built - Just the one small filter can packed with AC ( about a cup and a half) changed every 10 hours. I'm surprised there weren't more accidents.

That's why they had dip tubes! (for all the water which ended up in the tanks)

[rcontrera]

It's amazing how little filtration they used back when the compressor was built - Just the one small filter can packed with AC ( about a cup and a half) changed every 10 hours. I'm surprised there weren't more accidents.

What is amazing is that there are several compressors that have extremely wimpy filtration as they come standard out of the factory.

But, to be fair, we are a pretty tough creature and breathing a little water or stinky air may make us uncomfortable. But most of us old timers just "coughed it out" and moved on!