This section contains a general discussion of the essential elements that typically make up a working air compressor system and items crucial for proper installation and operation. It is intended to introduce the principal topics that should be considered in an air compressor project. An expanded technical discussion of these topics can be found in the section on Air Compressors. The general components of a compressed air system are illustrated schematically in the figure below.
A compressed air installation may consist of one large or multiple smaller compressors of sufficient size to meet the overall air requirement. Either motors or engines may be used as the driver. Hence, a prospective owner has a choice of electricity, gas, or oil for the energy input. The optimum installation is one which has the lowest combination of installation cost, maintenance cost, and operating cost.
The Conditioning/Drying stage is required to remove any particulate, water, oil or other contaminants that could damage or adversely affect equipment using compressed air. Pressure control is necessary to assure that proper air pressure is maintained in the system, while the end use loads of a system determine the installed capacity required (equipment diversity and system leaks must also be taken into account). Ventilation and heat rejection assure that the unit will run properly and not overheat.
The system also should have enough flexibility to adapt to the range of needs and load conditions of the site. The necessary information on load profiles and duration can be obtained from various sources, including interviewing plant personnel, reviewing plant logs, and examining air compressor unit operating conditions
A typical compressed air profile is presented in the figure below. From this profile, it can be seen that the peak load is slightly in excess of 1,500 SCFM, the minimum load is 1,100 SCFM, and the “average” load can be roughly estimated at 1,300 SCFM. This information is useful in determining maximum, minimum, and redundancy requirements for proper sizing of equipment, as well as determining the appropriate equipment technology to be selected.
For any type of compressor used, the unit should be mounted on a level solid foundation so that no strain is imposed on the base. Space should be provided on all sides for normal maintenance and proper air circulation. Compressors should be installed in clean, cool, dry locations which are well ventilated. Areas that have dirt, vapors, and volatile fumes should be avoided as they may clog the intake filter and valves. If this is impractical, a remote air intake should be used.
The compressed air distribution piping should be of sufficient size to keep the pressure drop through it to a minimum. The main air line should never be smaller than the compressor outlet size. All piping should be sloped to an accessible drain point, and branch or outlet lines should be connected to the top of the main so that moisture will not enter the outlet.
Many accessories exist for use in compressed air systems. Some are relatively common and will be found in almost every installation, while others are special purpose devices and may be found under certain circumstances. Locations and application of devices that provide the “conditioning/drying” system function can be found in the following schematic. Brief descriptions of these devices and their system functions follow the figure.
Aftercooler: Assists in the removal of moisture in compressed air. Aftercoolers remove moisture by lowering of the air temperature and may be of the air-cooled or water-cooled type.
Air Line Lubricator: Designed to inject oil mist into the compressed air system for the lubrication of air tools and equipment.
Automatic Water Valve: A valve designed to automatically control water flow to water-cooled compressors.
Belt Guard: A mandatory feature for all belt-driven compressor units where the flywheel and motor pulley belts are exposed.
Discharge Line Filter: Designed to trap foreign matter in the compressed air stream that may be harmful to pneumatic tools and equipment.
Dryers: Designed to minimize all moisture in compressed air systems. Many different types of dryers exist.
Filter: Assures foreign matter does not enter into the compressed air system. Many types are available, and should be selected based upon manufacturer’s recommendations.
Manual and Magnetic Starters: Provide thermal overload protection for motors and should be used as recommended by local electrical codes.
Moisture Separator: Designed to trap and expel oil or condensed moisture in a compressed air system. Expulsion of moisture may be manual or automatic.
Pressure control devices that are typically found in a compressed air system include the following:
Pressure Reducing Valve: An adjustable device that regulates a higher (and somewhat variable) initial line pressure to a lower constant secondary pressure.
Pressure Relief Valve: An adjustable device that relieves pressure beyond a specified upper limit and re-closes upon return to normal operating conditions.
Receiver: A vessel in which gas is stored under pressure as a source of pneumatic fluid power; may be classified as either “wet” or “dry” and refers to the position of the receiver relative to the dryer(s).
When examining the feasibility of installing additional or replacing existing air compressors, it is necessary to document the existing equipment. A Preliminary Data Entry Form (download PDF) will prove helpful in obtaining this information when performing field investigations. Not all sections of the form will be relevant to all projects, but the form allows for recording manufacturer, model no., capacity, and other technical performance information for all system elements.
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