Boosting Air Supply

You can step up to a beefier compressor, or you can tweak your setup by adding buffer air tanks and another small compressor to work in tandem with existing equipment. October 26, 2011

I'm looking to gain some air for the occasion when I need to run two air sanders, and wondered if an air tank would really be the answer (or if I should save my money for a screw compressor). My compressor is a 5hp, single stage, IR with a 60 gallon tank. Typically, we're only running one sander and it can be a hard day on the compressor if we're sanding all day long. Any thoughts? Budget is a big concern.

Forum Responses
(Cabinetmaking Forum)
From contributor M:
Sounds like you need more CFM. Average CFM for sanders is about 16 and your 5hp compressor is probably putting out at best about 18cfm. Adding an air tank would help but not as much as you might think. Air is expensive energy. Why pay the electric cost of a 5hp motor to run a sander?

From contributor G:
Understood. I'm also running a widebelt, hinge machine, spray rig, and other handheld air tools, so I'm committed to a compressor and like the sanding performance over an electric sander. Just looking for opinions on air tanks. This seems like the least expensive venture that can improve my situation.

From contributor L:
The air tank can even out short bursts of air requirements but won't probably help when talking about a second air sander. They are just air hogs. I also like the performance of the air sanders over the electrics, but you do pay for it. I went from a 10 hp recip to two of them, then to a 25hp screw, and still run short of air sometimes. Can't win! 16 man shop. Screws work best for more or less constant demand, i.e. bigger shops.

From contributor B:
What's the best alternative to a random orbit air sander, in electric? Are there any of them that can compare in speed and quality?

From contributor U:
Put in the air tank - it can't hurt. I have two 60 gallon tanks on not running compressors and one 120 gallon tank on a running compressor, in a two man shop. If you still run out of air, buy a bigger compressor and hook it up. All my compressors would run if I turned them on; I keep them as a backup.

From contributor Y:
You could run two 5hp compressors in sync.

From contributor I:
Adding a second compressor can be a good idea for a shop that has a highly variable air demand. It is also not as expensive to add another 5 HP compressor as it would be to buy a 15 HP compressor. I think you are a long way from needing a screw compressor.

From contributor N:
Look in to the new Mirka DC sander. I had the same problem of not enough air, and an overworked air compressor. The sander is not cheap, but should pay for itself in energy savings.

From contributor A:
If your business is growing, air will be in more and more demand. We started with a 5hp, then like you, we got 2 sanders and needed more air. We went to a used 15hp DeVilbis with an 80 gallon tank, then added a 120 gallon tank. All the tank did was even out the bumps, as was previously mentioned. Our 15hp was running 50% of the time and we were having pressure fluctuations in the sanding department. We now have a 20hp screw. All of our air issues are gone. We have had as many as 4 sanders going nonstop as well as odds and ends without any problems.

The 15hp cost us $2300, and the screw cost $6000. We kept the 15hp as a backup, but have not had to turn it on yet in the 9 months since we got it.

From contributor L:
If you buy a second recip compressor, put them both on an alternating switch system. When both are not needed, they will get used alternately and get to cool between starts.

From contributor I:
Great point, contributor L. Can you recommend a simple off the shelf controller that is easy to wire into the magnetic switches?

From contributor L:
The simplest controls only work well on matched compressors (two nearly identical compressors.) You can set one up using parts from Automationdirect. More complex systems that control mixed or more than 2 compressors should be left to the control designers. For controlling two very similar compressors you need to be sure you have adequate storage to prevent short cycling times. The pressure switches should be of the same type and also be matched in their in/out set points. All the simplest controls do is start or load one compressor and run it until either enough air is in the tank to shut it off or until it can't keep up with demand and then starts a second compressor. When demand drops, the first compressor is shut down or unloaded and the 2nd one continues to supply air. If demand rises above what compressor #2 can supply, compressor #1 is started/loaded. When demand has again been exceeded, compressor #2 shuts off or unloads and #1 carries the load. You can see that enough storage is needed to prevent the second compressor from very quickly bringing the pressure up to the shutoff point. That could start a series of short cycles and be very hard on motors.

Compressors that first go into unload operation before shutting the motor off are unlikely to suffer the short cycle problem. If this isn't making sense to you, call one of the large compressor dealers, not Home Depot. After installing the sequencing system, spend some time watching it run to be sure all is okay. Where you are likely to see a problem is the point where one compressor isn't quite enough.

From contributor I:
Thanks. I see there is a lot more to this than I realized. I am also looking to increase my air supply. I was just going to buy another compressor and set its cut in pressure 10 PSI higher than the first. The setup you are describing keeps the work load evenly distributed over the units.

I am still not at the point that a screw makes sense, but I expect to buy one in a couple of years. Until then I think having two compressors will give me the flexibility and efficiency I need.

From contributor L:

We kind of went the same route as contributor A over the years. When we moved to this shop (4000sq ft) I bought a 10hp on a 120 gallon tank. We expanded to 8,000 sq ft and I added a 2nd 10hp same as the 1st one. I tried the thing of just setting the pressure switches slightly different. That made the first compressor run most of the time and the 2nd one only at high demand times. After seeing how hot the one compressor would get running most of the time, I bought a used sequencer. That made things much better. We enlarged the shop twice more (to 25,000'), added more equipment and were running short on air. The worst was the CNC would stop if air dropped below 85#. Took the two 10s out of the compressor room and installed a 25hp screw, installed one of the 10s as a backup and use its tank as extra storage capacity. It can't be run at the same time as the screw as things are now arranged due to the differences in operating pressures. We are starting to run short on air again at peak times.

Compressed air is expensive! Additional items on our system: condensate water/oil separator, air to air cooler, coalescing filter, refrigerated air drier, main regulator, 1 1/2" primary piping, 1" secondary loop piping, several secondary loops (all 1" and smaller piping is copper), additional regulators, filters, oilers, all the quick couples, hoses, air tools, spray equipment, pneumatics on the stationary tools, eek! It's surprising that it all works as well as it does. We didn't have the refrigerated drier and coalescing filter until we added the second compressor. That improved just about everything downstream. Main reason we got the drier was to protect the pneumatic systems on the stationary tools. Turns out everything benefits.

From contributor I:
Thanks again. Is "sequencer" the technical name for this device?

From contributor L:
I think that is the proper term.