Advantages and Disadvantages of Each Compressor Type

Advantages and disadvantages of any compressor are based on its characteristics and application.

Advantages and disadvantages listed below are for a typical compressed air system in an industrial plant. The estimated full‐load bhp requirement of each compressor type at 100 psig discharge pressure at the compressor, a main drive motor typical efficiency of 92 percent and 0.746 kilowatts (kW)/bhp, the approximate operating costs of operation are obtained.

Single‐Acting, Air‐Cooled Reciprocating Air Compressors

Advantages include

• Small size and weight
• Generally, can be located close to point‐of‐use avoiding lengthy piping runs and pressure drops
• Do not require separate cooling systems
• Simple maintenance procedures.

Disadvantages include:

• Lubricant carryover as piston rings wear, which should be avoided
• Relatively high noise
• Relatively high cost of compression
• Generally, are designed to run not more than 50 percent of the time, although some can be at 80
• percent
• Generally, compress and store the air in a receiver at a pressure higher than required at the point‐of
• use. The pressure then is reduced to the required operating pressure but without recovery of the energy
• used to compress to the higher pressure.
• Operating Efficiency: 22 to 24 kW/100 cfm*

Double‐Acting, Water‐Cooled Reciprocating Air Compressors

Advantages include:

• Efficient compression, particularly with multi‐stage compressors
• Three‐step (0‐50‐100 percent) or five‐step (0‐25‐50‐ 75‐100 percent) capacity controls, allowing
• Efficient part‐load operation
• Relatively routine maintenance procedures.

Disadvantages include:

• Relatively high first cost compared with equivalent rotary air compressors
• Relatively high space requirements
• Lubricant carryover on lubricant cooled units
• Relatively high vibrations require high foundation costs
• Seldom sold as complete independent packages
• Require flywheel mass to overcome torque and current pulsations in motor driver
• Repair procedures require some training and skills.
• Operating Efficiency: 15 to 16 kW/100 cfm*

Lubricant‐Injected Rotary Screw Compressors

Advantages include:

• Compact size and complete package
• Economic first cost
• Vibration‐free operation does not require special foundation
• Part‐load capacity control systems can match system demand
• Routine maintenance includes lubricant and filter changes.

Disadvantages include:

• Less efficient full‐ and part‐load operation compared with water‐cooled reciprocating air compressors
• Lubricant carryover into delivered air requires proper maintenance of air/lubricant separator and the lubricant itself.
• Operating Efficiency:

18 to 19 kW/100 cfm, single‐stage*

16 to 17 kW/100 cfm, two‐stage*

Lubricant‐Free Rotary Screw Air Compressors

Advantages include:

• Completely packaged
• Designed to deliver lubricant‐free air
• Do not require any special foundations.

Disadvantages include:

• Significant premium over lubricant‐injected type
• Less efficient than lubricant‐injected type
• Limited to load/unload capacity control and VSD
• Higher maintenance costs than lubricant‐injected type over the life of the machine.
• Operating Efficiency: 18 to 22 kW/100 cfm*

Centrifugal Air Compressors

Advantages include:

• Completely packaged for plant or instrument air up through 500 hp
• Relative first cost improves as size increases
• Designed to deliver lubricant‐free air
• Do not require any special foundations.

Disadvantages include:

• Limited capacity control modulation, requiring unloading for reduced capacities
• High rotational speeds require special bearings, sophisticated monitoring of vibrations and clearances
• Specialized maintenance considerations.
• Operating Efficiency: 16 to 20 kW/100 cfm*

* By taking the estimated full‐load bhp requirement of each compressor type at 100 psig discharge pressure at the compressor, a main‐drive motor with a typical efficiency of 92 percent and 0.746 kW/bhp, the approximate efficiencies are obtained.