Dew Point?
January 26th, 2009How Low?
Here’s a tool question.
Sooner or later, I want to get an air dryer for my compressor. It will blow up to something like 17 SCFM at 175 psi. I keep the output at 125 psi or lower. It rarely goes above 95 degrees here, and it is extremely unlikely that I would trouble myself to work at that temperature anyway. The lowest temperature I am likely to put up with is probably 60 degrees, although it’s possible that I will move farther north, and that there may be times when I would want to use the compressor at lower temperatures. I very much doubt it, though, because I’d probably put a heater in the shop.
What dew point do I need? It looks like the choices are 38 and 50 degrees Fahrenheit. I don’t see myself doing any painting, but plasma cutting and sandblasting are likely to happen.
I think the little Harbor Freight machines are probably good enough. Everyone seems to like them. But sometimes you see something really nice on Ebay or Craigslist, for less money.
January 26th, 2009 at 1:02 PM
The HFT drier is fine. More than your compressor needs. 38 degrees will work ok.
January 26th, 2009 at 2:28 PM
Certainly a refrigerant type compressed air dryer will make super dry air, but a dessicant type using lithium bromide or molecular sive will generally do for most home shop air systems.
The industrial shops I work with usually only use refrigerant type dryers in their paint facilities.
Check out a good multi stage coalescing filter set up like those made by Devilbis and CHANGE the FILTER every once in a while, and unless you’re subcontracting for NASA or building race car frames using a computer driven plasma cutter table you should be OK–especially making bird gymnasiums and do dads to wheel you new milling machine around on.
You should also consider having a branch line that isn’t oil free or has an oiler built in for running air tools when you start racing the wooden car you build and have to turn some wooden lug nuts.
Hah…another good blog name…”Wooden Lug Nut.”
January 26th, 2009 at 3:03 PM
It’s hard for me to believe those little desiccant filters get the job done. Lots of water pours out of my tank when I open it up.
January 26th, 2009 at 3:13 PM
Steve,
Before you bother with an air dryer, install an air cooler. The easiest way that I know to do it is to get at least 20′ of copper tubing, 1/2″ or bigger, or use 20′ of 1/2″ copper pipe. Support it somehow so that it’s running ‘downhill’; feed the air from the compressor head into the top, connect the bottom to the tank, preferably down on the side. Take your air from the top of the tank for your tools. Take the compressor vibration into account so you don’t break the pipe/tubing; I’ve used hydraulic hose because I had it, and it’ll stand all kinds of pressure and heat.
The idea is to cool the air from the compressor so the moisture will condense out and be caught by the tank, where it can be drained off periodically. I also installed a 3/4″ air filter on the tank outlet to grab any leftover moisture before it hits my lines.
How good does it work? I had a Wilkerson air dryer that I got from the scrapyard and felt it’d be too much trouble to install, for no more good than it’d do. My air is pretty decent as far as moisture goes. Even if you decide to get an air dryer later, you should still have a setup like above.
January 26th, 2009 at 5:07 PM
I’m confused I guess. Normally on home and most industrial setups you don’t dry the air going into the compressor or the associated tank, you dry the air coming out of the tank into the air lines feeding your tools. Of course you can break the factory line connecting the compressor to the tank and install whatever you want at that point.
It’s normal procedure to drain the tank on little pancake compressors that you use to run nail guns and such every day for a few hours before you put them back in your truck or move them to the shelf in your basement or garage.
If you’re really worryed, simply cooling the air coming out of the compressor (it heats up according to the old physics equation PV=nRT when you raise the pressure for a given mass quantity) before it hits the tank will, as “jdunmyer” says, allow you to catch more of the water in the tank if you have continuous usage like an auto shop or a sandblasting or other production facility.
If you just turn your compressor on every few days and let it pump back up to 125 PSI or whatever and only run it for a few hours after that what’s the problem with filtering the air going downstream to tools and draining the tank to prevent excessive corrosion each time when you’re done?
I designed and built both refridgerant and dessicant type air dryers as my first job out of college and the paper mills & other industrial users always just had a few giant screw compressors and a big tank or two in each air station and they set an air dryer on the outlet of the systems to dry the instrument air going downstream to the sensors, controls, actuators, etc.
You’d have loved the power house in a paper mill because the entire piping system was “ground” and they had air line connections and welding electrode connections frequently all over the building on every floor. You just drug your tools, hoses, and welding cables around with you and “plugged” in near where you were working and struck an arc or turned a bolt with an impact driver.
just one man’s opinion…the air dryer will definitely give you the dryest possible air and I never wanted to imply otherwise.
January 26th, 2009 at 5:12 PM
I only mentioned the water in the tank because I figured it was a measure of how humid it is here. I’d say 70% is normal, and 50% is a special day worthy of celebration.
January 26th, 2009 at 5:54 PM
You’re on the right track regardless of the technology you employ. The refrigeration type air dryers cost money up front and cost money to operate. They’re also limited to the freezing point of H2O at the working pressure which is somewhere in the low 30’s after which you get Ice in the lines and everything stops up.
I get confused and distracted because we were working with systems in my professional endeavor that needed dew points in the 5% relative range…sometimes approaching less than 1% and dessicant was the only way to go.
Industrial dessicant air dryers have two stages and one stage is being “regenerated” with some form of heat (steam or electric usually) while the other stage is on line processing air…thus they also cost money to operate if you are getting a super low low relative humidity/dewpoint in your air.
Something I also forgot to mention is that you are in fact knocking the giant chunks of waterr out of your compressed air stream in the tank if the usage is intermittent because in fact the heated compressed gas is cooling off and the moisture is condensing inside on the tank walls–basically acting as a heat exchanger–not a bad thing as long as you drain the liquid and not let the tank corrode out and blow up.
Further elaborating on “jdunmyer’s” comment, I’d rather just buy a coil of copper pipe and connect it all coiled up downstream in the line between the compressor outlet and the “air receiver tank–the technical term” in the fashon of a moonshine still on the Andy Griffeth show.
When you’re not using it to cool air maybe you could cool wort or other beer byproducts…
January 26th, 2009 at 6:01 PM
The big deal, when I used to do air filtration systems (endustra filters) was to get your compressor intake air from a place where the air was drier. If it’s humid in the garage, plumb the inlet of the compressor to a non humid place- like in your house, or outside. Or you can make a cannister that holds silica gel or some other dessicant, and use it to filter the intake air, so less air has a chance to get into the compressor. Add an auto drain, and you have something that will remove most of your moisture. A small inline dessicant will then get rid of the rest.
Industrial applications sometimes cool and dry the air coming directly out of the compressor; that way no moisture ever makes it into the tank where it can do a lot of harm, eventually.
January 26th, 2009 at 9:24 PM
I’m having a deja vu. I thought we discussed this before when you bought the compressor. I remember after reading og’s comment that it was suggested then that you intake your air from the house (air-conditioned).
January 26th, 2009 at 9:56 PM
JD makes a good point except it is even easier and uses less space to use type L soft copper tubing. Type L will withstand higher pressure and the soft copper can be formed into a vertical coil that will do the same thing as a straight pipe run for cooling the air on the oulet side of the tank. Mount that inside an airconditioned closet so that it will constantly drain back into the tank of the air compressor. Use a suitable size of tubing like 3/4 ID minimum. That could even be made more efficient by installing a blower to change the air in the closet.
If you have your trusty Turbo Torch handy you can buy a tank of MAP gas and silver solder or braze the tubing onto whatever fittings you need.