Air compressor supplies air into a nail gun
Air compressor supplies air into a nail gun

An air compressor is a pneumatic device that converts power (using an electric motor, diesel or gasoline engine, etc.) into potential energy stored in pressurized air (i.e., compressed air). By one of several methods, an air compressor forces more and more air into a storage tank, increasing the pressure. When the tank's pressure reaches its engineered upper limit, the air compressor shuts off. The compressed air, then, is held in the tank until called into use.[1] The energy contained in the compressed air can be used for a variety of applications, utilizing the kinetic energy of the air as it is released and the tank depressurizes. When tank pressure reaches its lower limit, the air compressor turns on again and re-pressurizes the tank. An air compressor must be differentiated from a pump because it works for any gas/air, while pumps work on a liquid.

Classification

Compressors can be classified according to the pressure delivered:

  1. Low-pressure air compressors (LPACs), which have a discharge pressure of 150 pounds per square inch (10 bar) or less[2]
  2. Medium-pressure compressors which have a discharge pressure of 151 to 1,000 pounds per square inch (10.4 to 68.9 bar)[2]
  3. High-pressure air compressors (HPACs), which have a discharge pressure above 1,000 pounds per square inch (69 bar)[2]

Positive displacement compressors

Positive-displacement compressors work by forcing air in a chamber whose volume is decreased to compress the air. Once the maximum pressure is reached, a port or valve opens and air is discharged into the outlet system from the compression chamber.[3] Common types of positive displacement compressors are

Technical illustration of a two-stage air compressor
Technical illustration of a two-stage air compressor
Technical illustration of a portable single-stage air compressor
Technical illustration of a portable single-stage air compressor

Roto-dynamic or turbo compressors

Roto-Dynamic air compressors include centrifugal compressors and axial compressors. In these types, a rotating component imparts its kinetic energy to the air which is eventually converted into pressure energy. These use centrifugal force generated by a spinning impeller to accelerate and then decelerate captured air, which pressurizes it.

Cooling

Due to adiabatic heating, air compressors require some method of disposing of waste heat. Generally this is some form of air- or water-cooling, although some (particularly rotary type) compressors may be cooled by oil (that is then in turn air- or water-cooled).[4] The atmospheric changes are also considered during cooling of compressors. The type of cooling is determined by considering the factors such as inlet temperature, ambient temperature, power of the compressor and area of application. There is no single type of compressor that could be used for any application.

Applications

Portable diesel powered air compressor for powering tools, such as jackhammers
Portable diesel powered air compressor for powering tools, such as jackhammers

Air compressors have many uses, including: supplying high-pressure clean air to fill gas cylinders, supplying moderate-pressure clean air to a submerged surface supplied diver, supplying moderate-pressure clean air for driving some office and school building pneumatic HVAC control system valves, supplying a large amount of moderate-pressure air to power pneumatic tools, such as jackhammers, filling high pressure air tanks (HPA), for filling tires, and to produce large volumes of moderate-pressure air for large-scale industrial processes (such as oxidation for petroleum coking or cement plant bag house purge systems).[5]

Air compressors are also widely used in oil and gas, mining and drilling applications as the flushing medium, aerating muds in underbalanced drilling and in air pigging of pipelines.

Most air compressors either are reciprocating piston type, rotary vane or rotary screw. Centrifugal compressors are common in very large applications, while rotary screw, scroll,[6] and reciprocating air compressors are favored for small and medium sized applications.

Driver options

Air compressors are designed to utilize a variety of power sources. While gas/diesel-powered and electric air compressors are among the most popular, air compressors that utilize vehicle engines, power-take-off, or hydraulic ports are also commonly used in mobile applications.[7]

The power of a compressor is measured in HP (horsepower) and CFM (cubic feet per minute of intake air).[8] The gallon size of the tank specifies the volume of compressed air (in reserve) available. Gas/diesel powered compressors are widely used in remote areas with problematic access to electricity. They are noisy and require ventilation for exhaust gases. Electric powered compressors are widely used in production, workshops and garages with permanent access to electricity. Common workshop/garage compressors are 110-120 Volt or 230-240 Volt. Compressor tank shapes are: "pancake", "twin tank", "horizontal", and "vertical". Depending on a size and purpose compressors can be stationary or portable.

Maintenance

A small air compressor in use at a roadside tire repair shop in the village of Kodo, Niger.
A small air compressor in use at a roadside tire repair shop in the village of Kodo, Niger.

To ensure all compressor types run efficiently with no leaks, it is imperative to perform routine maintenance, such as monitoring and replacing air fuel management components and lubricant maintenance as well as draining water from the tank and replacing seals. Most air compressors can be operated by following the instructions from the included manual. It is suggested that air compressor owners perform daily inspections of their equipment, such as:

Air compressor isentropic efficiency

According to CAGI air compressor performance verification data sheets, the higher the isentropic efficiency is, the better the energy saving is. The better air compressor isentropic efficiency has reached 95%. [9]

Approximately 70~80% of the air compressor total life time cost is energy consumption, so using the high efficiency air compressor is one of energy saving methods.

See also

References

  1. ^ "How Do Air Compressors Work?". Popular Mechanics. 2015-03-18. Retrieved 2017-01-12.
  2. ^ a b c "Classification of air compressors". www.tpub.com. Retrieved 2017-01-12.</ref # Single-stage [[reciprocating compressor]] # Multi-stage reciprocating compressor # [[Compound compressor]]((clarify|date=August 2020)) # [[Rotary-screw compressor|Single stage rotary-screw compressor]] #Two-stage rotary screw compressor # [[Rotary vane pump]] # [[Scroll compressor]] #[[Centrifugal compressor|Centrifugal (roto-dynamic or turbo) compressor]] In another way of classification, there are two main types of air-compressors: oil-injected and oil-less. The oil-less (or Oil-Free) system has more technical development and delivers air of better quality for critical applications where oil contamination cannot be tolerated (such as food and medicine production) although it is more expensive, louder and lasts for less time than oil-lubed pumps. There are numerous methods of air compression, divided into either positive-displacement or roto-dynamic types.<ref>"Air Compressor Types and Controls". Natural Resources Canada.
  3. ^ "Compressor Selection Basics: Positive Displacement versus Dynamic Compression". Retrieved 2017-01-12 – via The 5th Utility.
  4. ^ "Types of Air Compressors". The Engineering ToolBox.
  5. ^ "Applications for Compressors". www.industry.siemens.com. Retrieved 2017-01-12.
  6. ^ Hislop, Reid. "Plug Power Places Large Production Order for Air Squared Compressors to be used in GenDrive Fuel Cell Units" (PDF). Plug Power. Plug Power. Retrieved 10 May 2019.
  7. ^ "Easy Guide To Rotary Screw Air Compressors For Vehicles – By VMAC". VMAC. 2018-10-16. Retrieved 2018-10-30.
  8. ^ "Evaluating True Horsepower and CFM Ratings of Air Compressors".
  9. ^ CAGI Performance Verification Data Sheets Archived 2022-01-21 at the Wayback Machine.