In today’s world of pneumatic operations, it’s hard to imagine that factories or workshops didn’t have air compressors. The fact is that air compressors are a relatively young innovation in the context of machine history. Not so long ago, air tools used in workshops typically got their power from complex systems made up of belts, wheels, and other large components. Most of the time, such machines were too massive, heavy and expensive for smaller companies and were therefore primarily limited to larger companies.
Today, however, Industrial air compressor are mostly found in factories that assemble products or in most places where cars are serviced, such as gas stations and auto repair shops. The list of tools that run on compressed air is long, but some of the most common pneumatic tools are as follows:
- drill
- Grinding machines
- Nail guns
- Grinding machines
- Spray guns
- Staplers
The main advantage of the standard shop air compressor is its compact and relatively lightweight construction, which is in contrast to central energy sources that generally use large motors. In addition, air compressors last longer, require less maintenance, are easier to move from site to site, and are much quieter than old-fashioned machines.
How the piston air compressor works
So how do air compressors work?
Air compression is essentially a dual process, i.e. increasing air pressure and decreasing air volume. In most cases, compression is performed using piston technology, which makes up the vast majority of compressors on the market.
Each reciprocating compressor has the following parts:
- crankshaft
- Connecting rod
- cylinder
- Pistons
- Valve head
Air compressors are mostly operated with either gas or electric motors – depending on the model. The inlet and outlet valves are located at one end of the cylinder. The two valves are shaped like metal flaps and are on opposite sides of the top of the cylinder. The inlet draws in air so that the piston can be compressed. The compressed air is then released through the outlet valve.
In certain models of air compressors, the pressure is generated with rotating impellers. However, the models typically used by mechanics, construction workers, and craftsmen tend to work with displacement, which compresses the air in rooms that reduce their space. While some of the smallest air compressors only consist of a motor and pump, most have air tanks. The purpose of the air tank is to store amounts of air in certain pressure ranges until it is needed to carry out work. The compressed air, in turn, is used to supply the compressed air tools connected to the supply lines of the unit. While all of this is happening, the motor will start and stop repeatedly to keep the pressure at a desired consistency.
What the reciprocating piston does effectively is creating a vacuum. When the piston retracts, the front space is filled with air, which is sucked in from the outside through the inlets. When the piston extends, this same air is compressed and thus receives the force to push through the outlet valve – at the same time keeping the inlet closed – into the tank. As more air goes into the tank, the pressure increases.
How lubrication works in air compressors: Oil-lubricated vs. oil-free
One of the most important things to know about air compressor maintenance is how lubrication works. For oil, the pumps can be divided into two categories.
- Oil-lubricated pumps: Oil splashes on the walls and bearings in the cylinder, ie in an oil bath. This is known as “oil-flooded” lubrication. Even if the piston rings are supposed to keep the oil away from the compressed air, tiny amounts can sometimes seep into the tank. In general, this type is more durable.
- Oil-free pumps: The bearings are provided with permanent lubrication. Although these require less maintenance than oil-lubricated pumps, they can be quieter and put more stress on the motor.
Flooded oil can be a mixed blessing overall. When it comes to using power tools that require lubrication, the presence of oil in the air stream can be beneficial. For the tools that actually need oil, in-line wells can be added that distribute the oil in even quantities through these tools.
However, there are some tools and operations where even the smallest portion of the oily mist can have undesirable effects. Certain tools, including nailers and grinders, are specifically designed to function without the slightest amount of oil. If the operation is painting or woodworking, any amount of oil will interfere with the process. For example, oil in the spray paint makes it difficult for coatings to dry or process evenly. Airborne oil can cause surface contamination on wood.
There are ways to prevent oil from entering the air tank under most circumstances, such as the use of air filters and oil separators. For critical applications, however, it is best to simply opt for an oil-free compressor with permanent lubrication on the bearings to prevent oil from ever damaging the air.
One and two cylinder air compressors
To serve the wide range of air tools on the market, air compressors are manufactured in both single and twin cylinder designs. However, compressors used by private craftsmen and contractors often contain two cylinders which function almost identically to single cylinders, the only real difference being that there are two strokes on each revolution. Two-cylinder machines, for example, that are marketed to the public also work in two stages, with a piston sending compressed air to another cylinder for further compression.
Most single stage air compressors have a preset pressure limit of 125 psi. When this limit is reached, a pressure switch turns off to stop the engine. In most companies, however, it is not necessary to even reach the pressure limit. For this reason, the air line of the compressor is set to a regulator where you enter the appropriate pressure value for a specific tool. The regulator is equipped with two pressure gauges: one in front to monitor the pressure of the tank and another pressure gauge at the end to control the pressure of the air line. In addition, the tank is equipped with an emergency valve that triggers with the pressure switch in the event of a breakdown. On some models, the switch can be connected to a discharge valve,which can help reduce the load on the tank when the machine is deactivated.
Unlike the automotive-type pistons of most compressors, some models use a connecting rod without an arm pin instead. On these models, the piston extends and retracts while leaning side by side as a circumferential seal keeps the air inside.
