The true workhorse of the compressed air industry is the reciprocating air compressor, aka the piston compressor. These compressors rely on piston-driven crankshafts to pressurize the air and simultaneously increase density while decreasing volume. Energy is stored in the air in the form of pressure and heat.
Reciprocating air compressors can come in different variations depending on the application and situational requirements. Oil-lubricated piston compressors are easily the most common in the 5-30 HP range. If you’d like to learn more about the types of different compressors, click here. If you are unaware of the differences and do not work in medical air or any other high-quality air application, oil-lubricated will most likely be the best fit.
Piston compressors were the industry staple for many years; in some industries, they still are. Typically, they are used with high compression ratios (discharge to suction pressure) without a high flow rate. This compressor works best for high-pressure low flow rate systems, which explains why it is the choice for 5-30 HP. These units move less air (CFM) than higher horsepower systems while keeping the air under similar pressure.
Now that you have a basic idea of what these compressors are, let’s get into the details of how they operate. For starters, take a look at the figure below to see the process of compression in a reciprocating air compressor
Before the process of compression can occur, air needs to be transported into the chamber so that it can be compressed and put under pressure. In reciprocating air compressors, this is done by the rotor spinning and pulling the piston down from the top. Suction will occur from this motion and air will start to fill the chamber until the piston reaches the farthest point from where the air entered.
As the rotor continues to spin and the piston head begins to move back up, the inlet is closed by the force of the piston. This allows for the piston to do its job by compressing the entire chamber full of air down into a much smaller space. In the diagram above, this air would then exit the first stage and continue on to the second chamber where it repeats the compression process in a smaller area to increase the overall PSI.
However, before the air reaches that second chamber, it makes a pit stop in the intercooler, not to be confused with the aftercooler. This phase is used to remove some of the excess heat from the air. When air is put under pressure, the energy that was already present is also being condensed together. This energy then has nowhere to go and so the molecules become excited and release heat.
Heat is a result of compression, and if you were to compress the air again without cooling it, the temperature would get up to extreme temperatures that your equipment would not be suited to withstand. Any time you have multiple stages of compression it is important to have the proper steps in place as well to keep the air within a manageable temperature.
Whether the air goes through one stage of compression or two, the outcome after the final stage will be the compressed air being moved downstream to be treated for use. This air can go directly into storage, filtration, or into another airline. Air has to keep moving so that the compressor can continue making compressed air to meet your demand.
Reciprocating compressors are going to be the cheapest initial investment, especially when you compare scrolls or variable speed drives. They have simple construction and have relatively easy maintenance. Even though these compressors may have more moving parts, those parts are relatively cheap, due to the more traditional design.
These machines are the go to for your high pressure low flow situations, and for systems that require intermittent use. The design is rather simple which makes maintenance easier because it is easier to understand.
There are a few downsides to going with a reciprocating air compressor that we do need to address. As much as we want one, nothing is a perfect one size fits all in this industry. Due to the nature of piston compressors, they are really noisy and often require their own room or a sound-isolating box to keep the noise bearable.
Not only are the machines loud, the air they create holds a lot of heat and has oil emulsified. This can cause high outlet temperature of the compressed air, and as we know this can hurt your equipment. The pistons are oil lubricated so oil gets in the air as part of the process. This can cause oil build up in the piping over time and hurt the health of your equipment.
If you are looking to get your hands on a reciprocating compressor, you came to the right place. Warthog is home to the best piston compressors on the market, with brands like Quincy, Atlas Copco, and more to choose from.
To get the best piston compressors available go here. If you need help finding the best fit, we have sales technicians standing by to assist you. Find the right reciprocating air compressor for your system.
From Quincy Compressors
The Words Warthog and the Stylized Warthog are Registered in U.S. Patent and Trademark Office. Reg. No. 7,109,357 and 7,109,356
