About Air Compressors: Single-Acting Reciprocating Type

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. 

Piston goes down: air draws in. Piston goes up: air is pushed out.

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. 

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

Types of Compressor image courtesy of the Compressed Air Challenge

Compressor internals image courtesy of h080Creative Commons License.

About Single Acting Reciprocating Compressors

Whether you’re new to the field of compressed air, an experienced technician, or just in the market for a new compressor, you may find yourself coming into contact with various compressor types.  Within the world of compressed air supply there are two types of compressors: positive displacement and dynamic.  These two compressor types branch off into several different variations, as shown in the chart below.

Compressor types

Positive displacement compressors increase air pressure by reducing air volume within a confined space.  In a positive displacement compressor mechanical linkage is used to reduce the volume of air (the fluid), which results in a change to the air pressure.  To think of it another way, the energy which is used to displace the air volume is converted into an increase in air pressure.

Dynamic compressors, on the other hand, utilize an increase in air velocity to cause a change in air pressure.  For a dynamic compressor, the fluid (air) is accelerated to a high velocity through a rotor or impeller.  The kinetic energy of the air is then converted to an increased potential energy/static pressure by slowing the flow through a diffuser.  The air at the outlet of the diffuser is the compressed air which is used to perform work.

The internals of a single acting reciprocating compressor.

Within this vast field of compressed air generation, one of the most common types of compressors is the single acting reciprocating compressor.  The term “single acting” refers to manner in which the cylinder inside of the compressor motor interacts with the working fluid (the air).  When the fluid (air) acts only on one side of the piston, the motor is referred to as “single acting”.  This type of motor relies on the load of the motor, a flywheel, springs, other cylinders, or some other device/momentum to return the piston back to its original location.

Single acting compressors can be air-cooled or water cooled, lubricated or non-lubricated, and packaged to provide a wide range of pressure and flow capacities.  Because of this adaptability, single acting compressors are quite common and serve a variety of industrial needs.

No matter the type of compressor on the system’s supply side, having engineered products on the demand side improves overall system performance and efficiency.  If you’d like to discuss engineered solutions for your compressed air system, EXAIR Application Engineers are ready and waiting.

Lee Evans
Application Engineer


Compressor internals image courtesy of h080, Creative Commons License.