Rotary Screw Air Compressors
If you're looking for an air compressor that provides a continuous output over a long period of time, consider rotary screw air compressors. Produced by established manufacturers that include Ingersoll Rand, Chicago Pneumatic, and Quincy, these machines are designed for constant use in a wide variety of demanding applications.
How rotary screw air compressors work
Traditional reciprocating compressors compressed air with one or more pistons that use an up-and-down motion to force air through the cylinder. Rotary compressors use dual counter-rotating screws to continually draw compressed air into specially designed cavities.
The main advantage is that the rotary compressor allows for continuous, uninterrupted use, rather than having to rest after a specific period of time. Plus, since the mechanisms are continually cooled and use fewer moving parts to operate, they have a 100% duty cycle. This is in comparison to a high-end reciprocating compressor that might have a 90% duty cycle - meaning it has to rest 10% of the time. A rotary compressor needs no such break.
Buying the right rotary screw air compressor is a matter of finding the ideal combination of performance and air yield. Sizes and performance are displayed on web sites or product literature, but not always in the clearest ways. So be sure to ask dealers about your exact requirements.
For example, let's say that you know you need a compressor that operates at 74 cubic feet per minute (CFM). You also need to know the optimum pounds per square inch (PSI) for your machinery or tools to work most effectively. Generally speaking, you'll want to leave room for growth in the CFM figure, should you require higher performance in the future.
Additionally, you'll find that these compressors are most frequently listed according to horsepower (hp) rather than any other guideline. For example, a compressor might run at 20 hp with 74 CFM at 125 PSI. Ideally, you'll want a machine that runs at the lowest possible horsepower for the other requirements you have. In most cases, you won't find a rotary compressor that operates under 7 hp.
Although rotary compressors are more expensive than their reciprocating counterparts, they boast a much longer operating life. Furthermore, buying used rotary screw air compressors can provide the same lifespan as a reciprocating machine and the cost will be about the same.
In many cases, small businesses or fledgling business owners are more likely to buy used machines to save money while still maintaining the same level of operation. This practice saves a little, but not a whole lot.
For new machines, expect to pay at least $2,100 for entry level models (3 to 10 hp), with average prices closer to $5,500 and as high as $7,300. Top-tier rotary screw air compressors run between $15,000 and $51,000+ for models that put out 50 to 100 hp+.
Used models, many of which are 20+ years old, can be purchased for 50% to 70% less than their new counterparts. For example, top-tier models that feature 30 to 50 hp, typically cost between $5,000 and $8,000.
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