Introduction
This is a 3D model of a Piston Air Compressor.
How Piston Air Compressors Work
The below video is an extract from our Mechanical and Electrical Engineering Explained Video Course.
3D Model Annotations
Piston Air Compressor
This 3D model represents a reciprocating piston air compressor. This type of compressor is typically used for delivering air for service applications (pneumatic actuation of valves, powering pneumatic hand tools etc.).
Suction Filter
Ambient air is drawn into the compressor through the suction filter.
Discharge
Compressed air is discharged from the compressor through the discharge port.
Transfer Connection
Air that has been compressed in the first stage piston, is transferred to the second stage piston via the transfer connection. The transfer connection has a grooved appearance because it is designed to transfer heat to the surrounding air; this increases the efficiency of the compressor.
1st Stage Compression
Ambient air is compressed in the first stage compressor. The first stage compressor piston is larger in diameter than the second stage compressor piston, because its discharge pressure is lower.
2nd Stage Compression
Compressed air from the first stage compressor is discharged to the second stage compressor. The second stage compressor piston is smaller in diameter than the first stage compressor piston, because its discharge pressure is higher.
Piston
The reciprocating piston compressor is one of the most common compressor designs used today. A piston air compressor will usually have between one to three pistons, with each being installed within a cylinder liner. A piston consists of a cylinder-shaped body, with piston rings installed around the main body (the piston rings are used for sealing the space between the piston and cylinder liner). A piston moves linearly within its cylinder, drawing air into, or discharging air out of, the cylinder.
Suction Valve
As the piston moves away from the suction and discharge valves, it draws air into the cylinder; this is referred to as the ‘suction stroke’. When the cylinder volume is occupied completely by air, it is said to be ‘charged’. Suction valves on this model are highlighted in red.
Discharge Valve
Once the cylinder is fully charged, the piston begins moving towards the suction and discharge valves; this is referred to as the 'discharge stroke' or 'compression stroke'. As the piston moves, it compresses the air. At a designated pressure, the discharge valve opens, and compressed air is discharged from the cylinder. Discharge valves are highlighted on this model in blue.
Sight Glass
Reciprocating machines (linear and rotary) almost always require some form of lubrication system to reduce and remove the heat generated between the machine’s parts. Air compressors are usually lubricated using some form of oil, often synthetic or mineral oils, but bio-degradable oils can also be used. A sight glass allows personnel to visually check that the oil level is sufficient for adequate lubrication to occur. Smaller compressors are usually splash lubricated, but larger compressors require dedicated lubrication systems. For special applications, compressors may require no oil for lubrication (‘oil free’).
Casing
The casing houses the eccentric shaft (similar to a crankshaft in an engine), piston(s) and bearings. The ribbed shape of the casing increases its contact surface area with the surrounding air, which increases the heat transfer rate of waste heat from the casing to the surrounding air (thus increasing compressor efficiency).
Motor
A 3-phase alternating current (AC) induction motor is used to rotate the chiller compressor eccentric shaft. The motor may be a direct on/off motor or controlled by a variable frequency drive (VFD).
Flywheel
An electric motor may be connected to the compressor shaft directly, or indirectly via belts and a flywheel.
Additional Resources
https://www.cp.com/en-in/compressors/expert-corner/blog/piston-air-compressor
https://www.popularmechanics.com/home/how-to/a151/how-air-compressors-work