Compressor Issues with Air-Powered Sanders
Pneumatic sanders use a lot of air, and can strain the capacity of some compressors. January 19, 2012
Question
Having recently purchased a palm air sander, I am finding that the compressor runs non-stop to keep up with sander (doesn't lose pressure, but doesn't shut off). The Baldor motor is rated at continuous duty, class F, and is within its amp rating while running. Compressor is heavy cast iron two stage. I’m wondering if I should be concerned about run times, or try to reduce cycling on/off? This motor is similar to cyclone which runs all day without shutting off. Any thoughts to life of compressor/motor running flat out for extended times? Also, at what point should I change oil in compressor?
Forum Responses
(Cabinetmaking Forum)
From contributor C:
I think your biggest problem is the air getting hot and producing a lot of moisture to the sander.
From the original questioner:
I've noticed the copper air line leading from pump to the tank is too hot to touch. However, the sander is a self-generating vac, and the air port on the sander is cold enough to condense shop air on it. Air from the sander exhausts 10' away in bag. I do have it running through a 4' coalescent bead hose to remove moisture. But does this affect pump in any way negatively or even sanded wood if not having water drop on it?
From contributor B:
Check your compressor manual. The compressor itself may have a duty cycle rating, of say 65-75% run time. Rings and valves may be affected.
That the copper line is too hot to touch is normal. As the air is compressed it gives off heat. As the air expands, at your sander, it absorbs heat. Think of how your air conditioner works - that's why it's cool.
From contributor R:
I think you already know the answer Nathan. 100% run time for a certain number of hours will shorten the life of the compressor. How much, don't know. I used to have two sanders running and the tank of my compressor could almost get to hot to touch. I think that is the reason Mirka's new electric sander is doing so well. You only have that little sander motor running. No 5 or 7 hp air compressor running, no filter maintenance, not nearly the noise. They are great little sanders.
From the original questioner:
Thet ShopTek screw looks great! Funny you should bring up the Mirka electric sander (CEROS). I have a 6" Porter cable and was considering the Mirka electric, but ended up going with Mirka 5" air with self-gen vac. I liked the portability of no vacuum, as well as ability to use in spray booth area. I may still get the 6" CEROS, as I think there are several sanders suited for different tasks (prefer the heavy PC to light Mirka when doing flat work with two hands). Less vibration and cuts as well if not better.
As for the air compressor, it doesn't say a duty cycle, but I would only be running for a hour or so flat out. Air tank gets slightly warm, but certainly not too hot to touch, like yours Contributor R.
From contributor R:
I have only tried the CEROS at a trade show, but was really impressed. It's very nearly the same weight as the air, and variable speed. That three year warranty makes it look even better. Our local supplier can't keep them in stock.
From contributor X:
I added an extra tank to my system giving it more capacity of air storage. Good thought on the electric sanders.
From contributor R:
I sold air compressors 30 years ago so this may be dated. Reciprocating compressors were designed for a 50% duty cycle and were more heavy duty then. You will burn up a recip compressor faster if you run it too much. Check your manual as to duty cycle. Less expensive machines run higher rpm to generate flow. These will burn up quicker. The pump is the bottleneck. Adding a tank is merely a buffer that will lengthen the time you can out draw the compressor and will lengthen the time to refill back to capacity once usage stops.
My neighbor recently built an unvented insulated room around his compressor to mitigate noise. I suggested he draw inlet air from outside. He did not. About 6-8 months later I came in one morning to hear a screeching sound. Turned out the pump froze but the motor was burning the belt up. Rotary screw compressors can run 24/7 with proper maintenance. I think they run more efficiently, so the power cost is a bit lower.
From contributor A:
Adding a second tank to the existing compressor usually does more harm than good. It makes the unit run longer to fill that second tank. Sure it may take a minute longer for it to "start" when you are using the sander, but it will run longer overall.
From contributor L:
Small shops generally don't have efficient compressed air systems. Typically the reciprocating compressor will be running too long at a time. It will be compressing air way above the pressures actually needed in the shop, wasting energy. Water vapor will not be removed before the tools. But in defense, compressed air systems are expensive.
While a very small shop may not be willing to invest in a complete system, shops with expensive tools should. CNC, beam saw, bander, bore and insert need clean, dry air for best results/life. Even your RO sander will have a shorter life without clean, dry air. Coalescing filters remove mist but not water vapor. The water vapor turns to water at the tool and damages bearings, etc.
From contributor F:
I've always wondered how the cost of use compares on electric versus air sanders. A 7hp plus compressor running versus the motor on an electric, plus the initial cost of the compressor.
From the original questioner:
Yes, I've wondered this as well. A large compressor running vs. small DC motor (in the case of Mirka CEROS electric) with shop vac. My (not so large) 3hp compressor runs nearly as long as I am using sander, at 12amp x 240v = 2880w (compared to the 400w dc motor, plus 1440w shop vac (12a at 120v).
So in reality my self-generated vac air sander is using 2880w compared to equivalent 1840w electric sander and vac. That's only 56% more power, much less than I was expecting.
I love the portability of my new self-gen vac sander. Not having to drag a vacuum along when I am going between rooms, or having to plug in vac and hook up hoses is nice and safer in the spray booth too.
