Types and operational principle of a piston air compressor

Zabidul Islam

An air compressor is a unit that provides potential energy by means of highly compressed air stored in an air tank under a certain PSI (Pound Per Square Inch) depending on the capacity of the tank and power of the motor. Later on, the air compressed under high pressure is utilized as energy to power air tools like nail guns, staple gun, blower and many more.
Once, the use of compressor was limited to automobile shop for flat tire inflation. With the advancement of science, the use of compressed air is explored and used in many applications using varied types of pneumatic tools.

Today air compressor is utilized in many applications like sanding, sinking nails of different gauges and sizes, removing lug nut, making a hole on wall or metal, and so many. Given that many homeowners, hobbyists, DIYers started to have this useful machine at their home. Fundamentally, an air compressor can be classified into 3 types: According to transported pressure, the design and operational principle and finally air compression ratio. Piston type, rotary-screw type, and vane type air compressor go under the third fundamental categories of an air compressor.

Among the three types, piston type and rotary-screw type compressors are commonly used out there. Whereas rotary-screw compressors are meant for heavy-duty applications in industries, piston-type compressors are engineered for light to medium duty applications in the home, garage, and gas stations.

Before demonstrating working principle of a piston type air compressor, it is pre-requisite to get introduced to the key mechanism of an air compressor. There are mainly three parts of an air compressor: the electric motor, pump, and the receiver (tank).

The main purpose of an electric motor is to power the pump via a flywheel and crankshaft. Basing on the nature of users, air compressor manufacturing companies have brought to market motors of different power sources. They can be gasoline powered, electric powered or even diesel powered.

The tank of an air compressor comes in varied sizes, shapes and built materials. The smallest air tank available in the market is a half gallon and there is no limit for the highest.  Air tanks having a 60-gallon capacity or more are generally placed vertically featured with a wheelbarrow so that users can haul it around with ease.  Commercial grade compressor tanks are constructed with cast iron to ensure maximum safety at the job site. Aluminum built tanks are also available but those are specially meant for domestic use to make the compressor light and highly portable.

Next is the pump which is the central components when it comes to an air compressor. The purpose of the pump is to compress air and drain it to the receiver. Pumps available in the market are profiled with either oil-lubrication feature or oil-free pumps. Oiled pumps tend to last longer than its counterpart oil-less pump.

Let’s plunge into the operational functions of an air compressor. A piston type compressor compresses air in a cylinder using a piston similar to automobile engines. There are few basic components in a pump that together complete the compression processing. They are a cylinder, connecting rod, piston, crankshaft, suction valve, discharge valve, and head. The pumps are perfectly sealed both internally and externally to make it airtight.  The piston rings mounted on a piston seal the cylinder from inside. A packing gland is used to seal the pump from outside.

One stage pump has one cylinder and two stage pumps have two cylinders installed either in V shape or in line.   Whatever the shape of a pump is, the inside of a pump is hollow round shaped like a pipe which is called cylinder. The piston moves up and down the cylinder to draw in and push out air. Piston’s one-time travel from up to down is called a stroke.

Both inlet and Outlet valves are located on the head of the cylinder. The backward moving piston minimizes pressures inside the cylinder, as a result, the suction valve gets open allowing air enter the cylinder. Similarly, the forward stroke pushes the air out through the discharge valve letting the suction valve close. Because of the pressure differences, both the valves get off and on synchronizing with the movement of the piston.

This part is completed by piston and cylinder. Then what is the functionality of other components? The connecting rod is attached to both the motor (via a crankshaft) and the piston. The motor converts rotational energy into kinetic energy causing the piston moves up and down. This process continues until the receiver or air tank gets refilled with the required amount of air volume.

Source: Air Compressor Agency

Zabidul Islam Razib is a freelance writer and can be reached at saiful431241@gmail.com

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