What To Look for in an Air Compressor
One of the most important elements in a well-designed mechanical services operation is the air compressor. While the specifications of many compressor models may appear similar, there are significant differences in design, controls, efficiency and intended use.
At the heart of a compressed air system is the compressor, which is rated by horsepower, capacity, pressure and duty cycle. These are good starting points when considering a replacement or additional farm and fleet air compressor, but other factors should not be overlooked.
Capacity vs. Pressure
Of the four rated specifications, capacity and pressure can cause some confusion. A compressor’s capacity is what gets the work done while pressure is how quickly it can do work. Adjusting discharge pressure upwards does not increase the compressor’s capacity
There are two common types of compressors, positive displacement and dynamic. Displacement compressors operate with a constant flow rate and variable pressure while dynamic, or turbocompressors, operate with variable flow and constant pressure characteristics. The two types of compressors are affected differently by variables such as inlet air temperature, air volume, mass flow and the pressure ratio of power consumption and performance.
Dynamic compressors are generally specified in higher base-load applications while positive displacement compressors are favored in variable load operations.
Positive displacement compressors are available as reciprocating, or piston-type, designs. Operating similarly to an internal combustion engine with a piston, cylinder and valves, reciprocating compressors are specified as single or double-acting type, single or multi-stage discharge, and air or oil-cooled.
Other reciprocating types include vane, rotary screw and gear compressors, each designed to address different operating requirements and energy efficiency goals.
Other considerations when specifying an air compressor include brake horsepower rating, or the power required at the input shaft, motor horsepower, which is the nominal rating for the engine, and a service factor percentage above its nominal rating. Efficiency rating is the compressor’s ratio of air delivered to brake horsepower.
Specifying the right compressor package can improve efficiency and reduce energy use expenses.