Rotary Screw Compressors Pros and Cons
Question (WOODWEB Member) :
I have run a larger IR (20hp if I remember correctly) at a larger shop, but currently own a Sullair shoptek unit (dryer and compressor mounted on 80 gal tank) 7.5hp. I have had the Sullair for about 3.5 years. I bought it because I really wanted a complete unit, not pieces parts that had to be plumbed together and also to be very quiet. It does all this well.
RS compressors are more costly to maintain, and are designed for continuous loading. While the Sullair has a good unloading system and burns the least amount of energy when unloaded, it still uses a bunch of power. If I had to do it over again, I'd probably get one of the newer quite Quincy 2 stage piston compressors as my load is generally more cyclic and I think both my operating and maintenance costs would be a good bit lower. I do like my RS compressor all the same and it makes me money. I'm not going to get rid of it anytime soon! Make sure your air system is tight and it will help you keep your operating costs down. I run my tank at about 150#, with a regulator on the output at #100. I feel this keeps my start stops to a minimum while giving air for nailing and stapling, but the compressor is not running continuously for that. Depending on your power company and meter type (demand or traditional) you may want to invest in a soft start as well.
From contributor G:
A month ago we installed a duplex compressor. It has two 10 hp pumps that are independent of each other mounted on a 240 gallon tank. One is a piston and the other a screw. We usually run the shop with the piston comp. When we need a large volume of constant air (when the RO sanders are running) we switch to the screw. A 15 or 20 hp piston comp would have been less expensive but I really like our duplex. It is the best of both worlds. Also, if one pump breaks down we are still in business.
From contributor L:
I think the above comments are pretty true. Screws do best when they have a more constant load. They cost quite a bit to maintain with oil changes, filters, separator elements and the like. There are a variety of controls that can reduce the electrical usage. Variable speed drives are offered for reduced loading conditions. Most screws max out at about 125PSI so if you want to let it run and then shut off and work from the storage tank, you've got to have a big tank(s.) If my shop air requirement was less than 60cfm or so and intermittent, I think I'd go for 2 10hp recips on an alternator.
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