My colleague, Tyler Daniel, wrote a blog “Intelligent Compressed Air: Double-Acting Reciprocating Compressor”, and I wanted to extend that conversation to a close cousin, the single-acting reciprocating compressor. As you see in the chart below, this type of compressor falls within the same family under the category of positive displacement compressors.
Positive displacement compressors increase air pressure by reducing air volume within a confined space. The reciprocating type of air compressor uses a motor that turns a crank which pushes a piston inside a cylinder; like the engine in your car. In a basic cycle, an intake valve opens to allow the ambient air into the cylinder, the gas gets trapped, and once it is compressed by the piston, the exhaust valve opens to discharge the compressed volume into a tank. This method of compression happens for both the single and double-acting reciprocating compressors. With a single-acting compressor, the air is compressed only on the up-stroke of the piston inside the cylinder. A single-acting compressor will have an operating efficiency between 22 – 24 kW/100 cfm of air. This type of air compressor is the most common and least expensive within the reciprocating family.
To explore the internals a bit closer, a mechanical linkage, or connecting rod, is attached to a piston and a crankshaft. For every rotation of a motor, the piston will move up and down. Air is being drawn into the cylinder and then compressed. The volume of the cylinders, the number of cylinders, and the rotations per minute will determine the amount of compressed air that can be produced. The advantages with reciprocating compressors are that they can produce high pressure, compress different types of gases, and have a cheap and rugged design. The disadvantages would be high vibration and noise levels as well as being oversized as compared to capacity.
There are different types of single-acting reciprocating compressors; single stage, dual stage, and multistage. The single stage uses one compression cycle to generate a pressure; generally for lower air pressures near 125 PSIG (8.6 bar). The dual stage will allow the pressure from the first cylinder to go into a smaller second cylinder. This dual compression will give a higher pressure up to 175 PSIG (12 bar). Multistage uses the same principle for multiple cylinders for much higher pressures up to 6,000 PSIG (414 bar); for applications like compressed air tanks used in SCUBA diving. They have options like air-cooled, intercooled, flooded type and oil-less. Single-acting reciprocating compressors have a wide range of uses and applications.
No matter the type of air compressor that you use, they are very expensive to use. Air compressors are considered to be the fourth utility within a manufacturing plant. To help use it efficiently and safely, EXAIR offers a range of products to clean, cool, blow, clean, conserve, and convey. This would include our Super Air Knives, Super Air Nozzles, Safety Air Guns, Cabinet Coolers, and much more. If you want to save energy, increase safety, and cut overhead costs, you can contact an Application Engineer at EXAIR. We will be happy to help.
Types of Compressor image courtesy of the Compressed Air Challenge
Compressor internals image courtesy of h080, Creative Commons License.