Air compressors have been around for literally thousands of years. Now granted the devices the ancients used for compressing air bear little resemblance to the modern air compressor. However, the basic principle is the same and without the primitive air compressors, civilization would not have evolved as fast it has. One of the primary uses for compressed air was to increase the combustion in a furnace.
The operator of a forge would use a bellows to blast compressed air into the furnace to stoke up the heat. This allowed ancient man to produce stronger and better metals for tools and weapons. Most people today would not equate a bellows as an air compressor, but that is exactly what it is. The blacksmith would pull apart the handles on the bellows and a check valve would allow fresh air to rush into the accordion like chamber. Then using muscles as the power source, the blacksmith would squeeze the handles together and the compressed air would shoot out the fitting on the end. Using this process it became possible to create a fire hot enough to smelt ores of copper, tin, lead and iron. Bellows are still used today in a variety of applications. The organ at your local church is probable powered by a bellows that is practically identical to one a thousand years ago. They even pop up in medical applications such as breathing machines in operation rooms.
It wasn’t until later in history that it became possible to compress air using mechanical methods. In the past, only human and animal power was possible to power crude air compressors and this severely limited the utility of these primitive devices. With the industrial revolution, the mechanical air compressor was born. Engines running from steam power became the first method to power an air compressor. One of the first uses of a steam powered air compressor was in underwater diving equipment. This opened up whole new methods for under water exploration and even underwater construction. The compressed air could be pumped down to a diver and allow extended stays below surface. Compressed air was also much safer to use as a power source for early pneumatic tools and drills. For example, early rock drills were powered by steam. However, hot steam is far more hazardous than compressed air. A ruptured steam line can kill or seriously injure a worker while compressed air is relatively benign. Steam powered rock drills eventually gave way to drills powered by air compressors.
As the internal combustion engine gained popularity, they began to be used as a power source for air compressors. Gasoline engines are today commonly used in piston type air compressors. This would be a common air compressor you would find in your garage or on the back of a service truck. The gasoline engine drives a crankshaft and piston. As the piston moves into the downstroke position, air flows into the cylinder on the low pressure end. When the upstroke begins, air moves into the high pressure.
This action produces compressed air. In larger industrial applications, a rotary type air compressor is used. Rotary air compressors produce compressed air by turning a vaned rotor inside of a long enclosed chamber. As the engine spins the rotor, air is sucked inside the chamber. The air is then forced down the vanes into smaller and smaller areas. This action compresses the air and forces it out the other end. Rotary vane air compressors work very well in industrial applications because they are capable of producing large amounts of compressed air for extended periods of time.
The air we breathe everyday is full of contamination. It has water vapor and airborne particulates that we inhale into our lungs. The vast majority is not harmful and we barely notice that its even there. However, to your air compressor these harmless contaminants can become quite harmful due to the compression process. During the compression process an air compressor concentrates natural contaminants in the air and this process makes them harmful to your air compressor and its components. Overtime they begin to erode your components, valves and be passed on to your air tools. Lets look at water condensation. Water vapor is a normal part of the air we breathe, especially if you live in a humid climate. It is harmless at normal atmospheric pressures. However when the pressure is raised in the compression process, hot air is pushed through hoses and fittings and when it contacts the cooler air condensation forms.
Water can be very damaging to your air compressor and air tools over time and removing it is a priority. Water is not the only liquid that can damage your system. Even, lubrication can cause damage if excessive amounts are in your air system. Older air compressors especially have this problem. As they get older and parts begin to wear out, lubricating oils leak into the compressed air can damage the unit. Don’t forget solids too. Rust, dirt and metal are all present and will attack your compressed air system. The results of air contamination are reduced efficiency and increased maintenance costs on both your air compressor and air tools. There are several ways to attack these problems and protect your air compressor. air compressor
Aftercoolers will cool the air temperature as it is discharged from the compressor. As a general rule for every 20 degrees F cooled, approximately half of the moisture is condensed. Aftercoolers bring discharge air temperature down from 200 – 400 degrees F to within 20 -50 degrees of the ambient air temperature. This process will cause most of the moisture to condense into a liquid state. Then the water can be removed from the system before it can cause any damage. An aftercooler can generally remove around 60% of the moisture from the air.
Dryers also remove moisture from the air compressor system by reducing temperature. Dryers generally remove around 30% of the moisture. This is in addition to the 60% the aftercooler removed. This is why you commonly see an aftercooler and a dryer both hooked up to an air compressor to produce the driest air possible.
Now that you are removing most of the water vapor from your air compressor using a aftercooler/dryer combination, that still leaves solid particulates in your system. These are commonly rust, metal and dirt. Lets face it, an auto shop is not the cleanest environment! Filters can be added to your shop air compressor to remove these particles. Filters do not condense water vapor and are only useful for solid particles. They are not a replacement for an aftercooler or dryer.