Screw Versus Reciprocating Compressors

Shop owners share thoughts and experiences with different air compressor technologies. August 31, 2009

I am looking at purchasing a new or used 10 -15 hp rotary screw compressor to replace my two existing compressors. I may keep one of the existing as a backup and additional air storage. I also need a dryer. I'm favoring the Kaeser setup. They seem to be showing up on the auctions fairly regularly. Any advice, input, war stories, etc. would be appreciated.

Forum Responses
From contributor B:
I have had good luck with Joy screw compressors. I would say that a 10 hp screw compressor will replace a 20 hp regular air compressor. Screws put out a lot of air. They seem to last a long time. The thing I can say is that they are louder than all sin, so you might want to make sure they are boxed. Other than that, the only problems I have had were with the oil separator, but it was an easy, inexpensive fix. I think a screw compressor is a good solution for your shop.

PS: I think most screw compressors already have a dryer on them. I am not really familiar with Kaeser. All I know is Joy Twist Air.

From contributor A:
I know very little about screw compressors, but I would say without a shadow of a doubt, keep an old one for a backup. The switch died on mine and wow, did we miss it!

From contributor D:
We have a Kaeser 15 hp air tower with dryer. I think it is good quality. I've had one minor problem with the air filter, which was getting dirty with oil from the compressor, and no one from Kaeser could find the cure. I found a solution by myself. One other problem we had this year is the compressor for the air dryer broke, and you know what? Not covered in the 5 year warranty (I know, I should have read the fine print). Besides that, it has run very well since June 2005.

From contributor R:
Some thoughts: Our screw compressor is quieter than the compressor it replaced (both are 15 hp). It may be a little higher pitched sound, but I think quieter. HP is HP; my 15 HP screw compressor is rated basically the same as the reciprocal. However, screw compressors are designed for non-stop running, actually the more the better, whereas my old reciprocating was designed for 65-75% duty cycle.

From what I could tell, Kaeser is a good brand. However, we found Atlas-Copco to be a couple of thousand cheaper; and At-Cop is one of the largest, if not the largest, compressor company in the world, so I don't think we have anything to worry about there.

If your compressor is running a lot, then a screw is a good choice. Otherwise I think you'd be better off with a reciprocal.

From contributor W:
Find a local compressor expert. The best kind is the guy that works for himself and has been doing this for 20 years. Ask him for guidance and help in finding a used screw/rotary compressor. He will help you with the maintenance, and will be there when it stops running.

From contributor L:
If you have a fairly constant need for air, a screw is good; if not, use a recip. If you get a screw, get one with controls that shut it down or unload it when demand is low - it will save a lot on electricity. Higher quality screws have larger air ends that turn slower and last longer. I bought a cheaper 25hp screw to replace 2 -10hp recips. Attached one of the recips to the system as a backup and plumbed as extra storage. Put an isolation valve on the screw for when you are using the backup recip to prevent over pressure at the screw's tank. Now wish I had bought a higher quality and larger screw. The good thing about the screw is it can run at full output endlessly; not true with a recip. Maintenance costs with a screw: 5 gallon oil change with synthetic oil at $300/5 gallons, replacement separator element at $? (don't remember, but was shocked), replace oil filter at $30. Air filters are several times more expensive than on the recip. Oil change interval 4 to 8,000 hours, filters more often. Use the free oil analysis from the company. Keep the machine cool for longer oil life.

We have our compressor in a separate room to control the noise; it needs a lot of airflow to cool the compressor. We keep most of the dust away from the compressor by having filters into the room. Installed a high temperature warning light and buzzer outside of the room, since no one typically goes in there after starting the compressor in the morning. The compressor has a small air to air cooler but we kept our big air to air cooler in the line, then through a coalescing filter, then a refrigerated drier, then the main regulator and to a looped copper piping system. The compressors, air-to-air cooler and refrigerated drier all drain their condensate into a Kaeser oil separator. That way we can dump the condensate down the drain and only have to pay a little for sending the filter out. Compressed air gets expensive!

From contributor K:
Kaeser is the best around. We bought a 25 hp Kaeser which was way too much compressor, and then switched to a 15 hp Kaeser variable and are very happy. Screw compressors make tons of air, so don't oversize your needs because compressors are expensive to run.

From contributor T:
I just installed a solo 10 hp variable speed. Wow - this thing is silent. You can actually talk on the phone while standing next to it. This one you can program yourself. Shuts off 60 seconds after unloading. Cost was 3000 new off of eBay. Best money I ever spent.