In our daily lives, tasks requiring compressed air arise relatively rarely. For maintaining tire pressure in our cars, or inflating an air mattress or small rubber dinghy during vacation, an efficient small electric air compressor would certainly come in handy—one that could also be useful for bicycle maintenance.
It is a fundamentally important tool for model makers as well. Spraying paints today is almost exclusively achievable with compressors designed for this purpose, but compressors are also indispensable tools for airbrush professionals in nail salons and automotive design workshops. Decorative painters also use them with great preference. In smaller workshops, higher-capacity versions are employed for various cleaning operations, operating pneumatic tools—such as driving screws in and out, sanding, etc. For correcting paint defects, higher-capacity compressors are essential. Purchasing them from specialized stores poses no difficulty, but selecting the appropriate type is important.
The obvious solution is to always choose a compressor with the most suitable capacity and operating mode for the anticipated tasks. If we need compressed air only briefly and relatively infrequently, a good-quality automotive compressor providing 2–3 bar pressure will meet our needs. These receive the voltage required for operation from the car’s 12V cigarette lighter socket, but they also work when connected to a battery charger. They are simple devices: their DC motor moves a small piston to produce compressed air, and they can typically be operated for a maximum of 20 minutes. This is not set in stone, of course, but prolonged operation makes them prone to overheating, which can cause premature failure.
Since they lack a reservoir tank, the air supplied flows out through the hose in pulses. Some do not even have a pressure gauge, and thus do not allow pressure monitoring, for example. However, versions with pressure gauges are suitable for this purpose even after the small compressors are shut off. A check valve in the cylinder prevents air backflow, and the pressure gauge indicates the pressure in the hose.
It is advisable to choose a type with robust construction capable of producing up to 3 bar pressure, and which can be made suitable for inflating other devices with various adapters that can be attached to its hose. Apart from blowing air—due to their pulsating operating mode, uncontrollable pressure, and lack of a buffer tank—they are not suitable for other purposes.
However, if we need to solve tasks requiring continuous and regulated air pressure, albeit not very high, then a compressor with more sophisticated construction that also includes a reservoir tank is the appropriate type. These are the so-called airbrush compressors, which can be used intermittently but for longer periods and are capable of producing 3 bar pressure.
In terms of design, either a diaphragm or a traditional piston provides air compression. These compressors are mostly necessary for fine painting work. They are indispensable tools for artistic automotive decorators, nail and face painters, as well as modelers. With proper maintenance, piston compressors have a longer lifespan than diaphragm ones. Their construction is similar to piston automotive compressors, but here the pressure gauge, reservoir tank, pressure-regulating valve for the supplied air, and an automatic switching system ensuring gentle operation are virtually indispensable.
Mains voltage is required for their operation. For prolonged work, automatic models are suitable. In such cases, the volume of the reservoir tank is decisive, which can be as large as 10 liters. The compressor motor is started automatically by the pressure sensor. As soon as the air tank reaches maximum pressure, it shuts down the drive motor, then restarts it at 1 bar pressure. The working pressure of the compressed air can be set with a separate regulating valve to match the paint’s consistency or type, and in more sophisticated models, the air passes through a separate filter before reaching the spray gun.
Their hose connection is typically 1/4″, but various adapter fittings can be purchased for smaller vinyl hoses. The noise level of airbrush compressors is generally 35–45 dB, which is considered low, so their operation is not burdensome in the workspace. These compressors are specifically designed for smaller-scale and precision painting work and can only be used with specialized paint spray guns.
For producing compressed air at higher pressures than the previous types, only industrial-scale compressors are suitable. These are generally capable of producing 8 bar pressure. Air compression is performed by a cylindrical piston equipped with cooling fins. There are also twin-piston models, but those are specifically required for industrial activities. The piston performing compression is driven by electric motors of various capacities, depending on type and capacity, typically 230V, 1.1–2.2 kW. The valve system of the compression cylinder in such devices is already sophisticatedly designed and has a long service life.
Among these devices are so-called oil-lubricated compressors, where the piston’s movement and the durability of its seal are ensured by oil lubrication due to high rotational speed. These require an oil filter before the outlet connection. The tank volume is essential. Although some hobby-grade, high-capacity devices have neither an air tank nor a pressure-regulating unit, the pulsation of the compressed air produced is barely noticeable, which causes no problem for cleaning blow-off operations. However, most hobby-grade compressors have at least an 8-liter air tank, which already provides continuous air at a pressure that can be monitored and regulated with a manometer. The air tanks of high-pressure compressors suitable for continuous use range from 50 to 200 liters, but these are specifically for industrial use, and their cooling is accordingly provided by a separate fan.
The drive motor’s operation is stopped by an automatic system and also switched on when pressure drops. The larger the air tank, the less frequently the compressor motor switches on automatically, depending on the amount of air consumed. The drain valve is a standard accessory of the tank, which is generally corrosion-protected due to condensate water, at least on more sophisticated devices. Condensate water can be removed through the drain valve.
When selecting compressors, it is advisable to decide based on the specifications characteristic of the type. Pressure is generally 8 bar, motor speed is around 2,900 rpm, and their power ranges between 750–1,500 W. Continuous operation of the devices is not possible for hobby-grade compressors due to inadequate cooling and lubrication, but presumably it is not necessary either. The volume of air supplied is also important for rapid tank filling, as is automatic operation, which means that when the tank reaches maximum pressure, it automatically shuts down and then restarts the motor when the safe lower pressure is reached. A pressure-reducing regulator is required for regulated-pressure air. The tank pressure can be monitored with a separate manometer, and the outflowing air pressure with another gauge.
The supplied air is cleaned of dust and oil contamination by a separate filter. The noise level of compressors is not an insignificant consideration either, although manufacturers rarely specify this, but if they operate directly in the workspace, it is worth paying attention to this factor as well. And finally, price can also be decisive. Every compressor will last for many years, but after that, instead of costly repairs, it is worth considering purchasing a new, relatively inexpensive device.
source: http://ezermester.hu