Filter/Driers

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rcs9250

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Jan 20, 2019
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Mentor, Ohio, United States
Small, low price, low CFM compressors and boosters for airgun charging seem to be getting more and more popular. I used to work in the scuba industry and moisture removal was paramount. The airgun market compressors typically have a bleeder for condensate that is manually or automatically operated depending on model. Though I’ve never had my air tested from my Omega Air Charger or my Umarex Ready Air, I suspect it still has moisture in it.

I recently purchased a dessicant (molecular sieve) filter drier from Joe Brancato and am in the process of setting it up so I can top off my 74cf carbon fiber tank

I’m curious how many air gunners add post compression driers on their compressors or do they just figure bleeding every five minutes is adequate. To my knowledge, every scuba compressor I see always come with a dessicant drier and often times a centrifugal water seperator. As mentioned, in scuba, moist air can create ice in a regulator during a scuba dive in colder water causing a freeflow of air.

Randy


 
Most condensate removers on compressors rely on a centrifugal method of separating moisture from the air. While they can remove a degree of moisture I believe a desiccant or molecular sieve filter is a must because as the air cools additional water can condense. The biggest problem that I see with them is that they add to the fill time as the volume they contain also has to come up to pressure. I started out with a standard size one from ebay but ended up finding a smaller diameter one that takes cartridge filled with molecular sieve that has significantly reduced my fill time. I would rather change the cartridge more often.
 
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My daystate MCH-3 has a water separator but no filter. I added another combo pack air water separator and filter plus I take desiccant tower.

C869E768-1385-49A8-94B8-522704EAF788.1625309685.jpeg

 
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In addition to purging my Yong Heng every five minutes of use I change my small cotton pre-filter every twenty. This has allowed my desiccant filter to survive for a year. When the small filter on top gets damp, which will be soon, I will replace the cartridge in my Tuxing filter. I fill at 65-70F and 55-65% humidity. I seldom run my compressor over twenty minutes a week.


 
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Dead On Shot,

Yeah, one of my considerations when buying the drier was the additional volume a drier takes up. I wasn't really concerned with the driers volume because an important thing on molecular sieve driers is they must be kept at a minimum 1700 psi after initial pressurizing. If pressure is not maintained the water drop out of the sieve and bad things can happen, as in potential BOOM. Molecular sieve beads should never be wetted with liquid water. Your typical set up with a molecular sieve tower is to have check valves and a PMV (pressure maintaining valve) so that once the compressor turns off the pressure stays in the drier, then once the compressor turns on at your next session it only has to re-pressurize a few inches or so of small lines. On my setup, in addition to the PMV I added to Sherwood high pressure valves on the input and discharge side of the drier to guarantee I don't loose pressure between sessions. 

As soon as I get my set up complete I'll post some pictures. 

dc8cappie and biohazardman,

Nice setups you have. Also forgot to mention above that the molecular sieve driers MUST be vertical at all times. One thing I changed on the plumbing that Joe Brancato did was put a tee at the bottom of the drier that one side went into the drier, then a straight down leg went to a drain valve and then the one that tee's to the side (horizontally) and then straight up to a male Foster fitting that is the air input so that all condensate went down and not into my valving.



Randy
 
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The key here is to understand moisture and the beast it really is!

Lets say you have ambient air at 30% moisture, compress that to 10 times to 150psi and oops now you're at 300%.

Between a shop compressor and a booster you can add large volume silica gel "scrubbers" to reduce that to under 10-20%.

But boost that another 10 times and you're still way above and at 4500psi you're at (30 x 10-20%) and need a final desiccant filter bad!



Good compressors have a priority valve, back pressure valve or pressure maintaining valve, it works as follows: It will block any pressure under 150-170bar~2175-2465psi, thats it. It forces the air to compress to a degree where (most all) moisture will condensate and can be drained. It will fill an empty bottle the valve just maintains the minimum pressure in the compressor output line thus always condensing moisture.

On the small compressors that have the little "handgrenade" that holds no more than a big tampon. Check/change this often! When it gets filled with water it will restrict airflow and compressor pressure can spike fast. Several here has had to change the pressure gauge because it shot through the roof and got permanently damaged.
 
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If you’re dive shop is pumping Grade E air, you have nothing to worry about. If you’re in doubt, ask to see their air analysis printout. Industry standard is quarterly so checking the date is key. If you some how wrangle a fill from the local firehouse, grade D is the standard for SCBA air, which is also acceptable.

My local dive shop (LDS) only fills to 3442psi so I can’t use them. Plus, they require yearly tank inspection, referred to as VIP, which stand for Visual Inspection Program ( or Plan). 

If you have a shop that fills to 4500psi, that’s pretty good

Randy


 
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Kball,

Yeah, 4350 might be the cool down pressure. Technically by DOT regulations, as I was taught in tank inspection classes, it is illegal to fill a tank over the specified max fill pressure in anticipation of pressure drop from cooling. Proper method is a very slow fill or fill, let cool, then top off. Most shops hot fill to a couple hundred psi over and then hope it is at desired max fill psi. 

That’s one thing nice about my Omega when filling to 4500psi, because it’s not a high cfm that fills it quickly the tank cools while filling. But then I only fill in 15 minute runs to help keep compressor cool too. 

Randy
 
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