Air compressors are used for a variety of different situations — in gas stations, manufacturing companies, and home workshops or auto stations. There are models made to handle jobs everywhere from inflating tires and toys to powering heavy duty construction equipment like sanding tools, drills, wrenches, staplers, and nail/brad guns. You can find them at your local Lowe’s, Home Depot, or other tool dealer shop. Here’s a basic run down of how air compressors work.
How do air compressors operate?
Air compressors basically operate on a simple idea: when air gets compressed, the volume goes down and the pressure goes up. The piston is how this compression happens, and typically, the compressor will have a reciprocating piston. There are rotating impellers within the compressor for certain types as well. Reciprocating pistons have crankshafts, connecting rods, pistons, cylinders, and valve heads. A source of power is necessary to get the unit to function. The power source is typically electric or gas. There is also a tank to store air within the unit.
At the top of each cylinder, you will see the valve head containing the inlet and the discharge valve. These are essentially metal flaps that will open and close depending on what type of movement is necessary. When the piston moves within the cylinder, vacuums are created.
The difference in pressure between what is inside the cylinder and what is on the outside is what allows atmospheric pressure to get the inlet vale to come open. Air comes into the vacuum space area and gets compressed by the piston, which goes up now. Then the inlet value closes and the discharge valve opens instead. Compressed air is then stored within the tank, which increases air pressure in the machine.
Read Also: Size, Power and CFM of Air Compressors
Single and Dual Cylinder Versions
In general, compressors will have one or two-cylinder versions to ensure they meet tool requirements. For homeowners and independent contractors, 2 cylinder models operate very similarly to 1-cylinder version. The only difference is that there are 2 strokes per revolution. Compressors also use a pressure switch to make the motor stop when tank pressure goes to a certain limit, around 120 PSI for single stage units. The air line has a regulator which is set to be in accord with the PSI needs of whatever tool you want to use. Gauges on the tank will tell you how much pressure there is, and another gauge will motor air line pressure.
A lot of piston compressors have oil lubrication – essentially an oil bath that will lubricate the inner workings of the unit, including the cylinders and the bearings. Pistons have special rings, which contain the compressed air over the piston to keep the oil separate from the air.
Determining how much power the compressor has is done through motor horsepower. You also need to know the volume air that gets delivered in cubic feet per minute, known as the CFM. Atmospheric pressure determines just how fast the air will move into the cylinder, so CFM can change a bit. It is depending on the humidity of the air and what the current temperature is. So standard CFM will start at 68 degrees with 36 percent humidity, and as the pressure goes down, the SCFM goes up.
Identifying Parts and Size
The pump is generally metal and has fins that come out on the side or the top. Smaller compressors also have pressure switches, which turn the unit on and off. If it goes below a certain level of air in the tank, it will come on and rebuild the pressure in the tank. There are basically three types of pressure delivering tanks: low pressure, which put out 150 PSI or lower, medium pressure, which put out anywhere between 151-100 PSI, and high pressure, which go over 1000 PSI. There are also rotary screw compressors and turbo compressors.
Electric and Gas Compressors
You will generally find 2 different types of air compressors: electric versions or gas version. Gas and diesel powered unites will often be found in areas that can’t get easy access to electricity, and are louder, requiring exhaust gas ventilation. Electric versions are found often in production areas and garages, as well as auto shops and construction site. You will find pancake, hot dog, twin tank, and wheelbarrow style compressors. They all essentially function the same way, so as long as you know the basics, you’re all set.