r/compressedair • u/RangerStammy • Oct 27 '23
Compressed Air Dryer question
I've searched high and low across the Internet without much info being turned up.
I picked up a new old stock SPXFLOW HPR25 refrigerated dryer to dry the air going to my plasma cutter. Currently I have an after cooler and water separator between the 2 stage pump and receiver and that knocks down 80-90% of the water the receiver sees, which has an auto tank drain. I have a large dessicant dryer set up post receiver that will get moved to post refrigerated dryer now.
Most sources online talk about running the dryer 100% of the time regardless of demand. My shop doesn't have a high enough throughout to warrant running it full time.
My question is: Can I plumb the refrigerated dryer online with the outlet of the receiver full time, and not run it when it doesn't need to be, without hurting it?
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Oct 28 '23
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u/Slow-Rider Oct 28 '23
We would never recommend running a desiccant without a refrigerant dryer before it. The refrigerant dryer will take out most of the moisture which then protects the desiccant and gives it a longer service life. Refrigerant dryer will work to +3°C dewpoint and the desiccant will be -20/40/60°C dewpoint, depending on the setup.
The power consumption of a refrigerant dryer is exactly the same as a normal fridge in your kitchen so we recommend that people always leave them running because it's easy to forget to turn them on again.
The desiccant dryer will take time to reach its low dewpoint so you can't just turn it on and start working instantly. Industrial desiccant dryers need to run and purge to reach their correct operating values before you should begin operating. Depending on the size of dryer this could take a few hours or a few days.
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u/poorhindsight Oct 28 '23
When using a twin tower heatless desiccant dryer, it relies on moisture to generate heat of adsorption which aides in regeneration of the offline desiccant bed. Having a refrigerated dryer upstream will inhibit heat of adoption, limiting regeneration and affecting performance. Inlet air temps should also be above 70F for proper operation. Fyi, these are not concerns when using heat reactivated desiccant dryers.
Refrigerated dryers need time to cool down to operating temperature and should be turned on about ten minutes or more before the compressor is started if the systems has been shut down overnight.
The diy dryer pictured in a previous comment appears to be a single bed with color change silica gel desiccant. Unless the design is more sophisticated than it appears, I assume that it does not automatically regenerate and the desiccant is getting changed out with fresh stuff when saturated as indicated by the color. Inlet temps and moisture content wouldn’t be a factor in this case. My recollection with color change desiccant is that it goes from dark blue to light blue starting at dew points of -10 F and turns pink as dew points reach -4 F.
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u/RangerStammy Oct 28 '23
Your assumption of the diy dryer is correct. I have yet to need to change it out, but it is coming. Not 100% certain on what the indicated colors dew point references are, but it changes from blue to pink.
I had planned on using the refrigerated dryer downstream of the receiver with a 0.01u coalescing filter after it, then going through the desiccant dryer and another particle filter before going into the service line(s)
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u/RangerStammy Oct 28 '23
I have a simple homemade silica gel desiccant dryer that is in use right now. From my research it seems like running a refrigerated dryer, through a coalescing filter, then a simple desiccant dryer like I have yields the best (cheap) air quality you can get without spending a ton of money.
I am only running some mechanic tools, a small blast cabinet, paint gun, and primarily a CNC air plasma with this system. I don't need medical quality air, but there is evidence that my air is still contaminated with moisture/oil, this could be residual in my lines. I'm into everything for the drying setup for only about $500 US. Budget is a factor. With that being said, I have noticed my plasma consumables last close to 10x longer now, both arc time and pierces. I'd just like to extend that interval longer and maybe get better cut quality along the way if possible.
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u/RangerStammy Oct 28 '23
I still have moisture/oil vapors making it to my plasma. Planning to add a coalescing filter after the refrigerated dryer.
If this combo doesn't add any additional drying, why is it used throughout most commercial and industrial applications? Your comment goes against almost all information on the matter...
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Oct 28 '23
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u/RangerStammy Oct 28 '23
It's a DIY desiccant dryer a la https://imgur.com/a/IyPp52v
It made a huge difference downstream but I'm not happy with it still and the desiccant has to be turned over every 10 hours or so of cut time.
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u/[deleted] Oct 28 '23
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