Reciprocating air compressors are just one of a variety of styles of air compressors available to those requiring a compressed air source.
This page is written to provide information about reciprocating air compressors. Better understanding of them will help in the selection of the right compressor for your use and may also help in troubleshooting of this type of air compressor.
First things first, however.
If you are in the market for an air compressor, spending time examining the huge variety and styles of compressors may not be productive if you do not know the answers to the following questions:
- What is the flow rate you need for your air tools or to run your plant, now and for potential future expansion
- At what air pressure do you need that flow
Having the answers to these questions up front will help narrow the range of air compressors you need to look at.
Then you will look for units with the following characteristics:
- A compressor that fits your budget
- One that fits into the area where you would like to install it
- Perhaps a compressor with the lowest up-front cost
- Or a style that has the lowest maintenance / operating costs
- You may want a compressor that is very quiet
- Or one that provides ultra clean or breathable air
Once you have determined the parameters of your compressor needs, then you will pointed in the right direction for the right kind of compressor.
OK, back to the reason for this page.
What is a Reciprocating Compressor?
A dictionary defines reciprocate to mean to move something alternately back and forth.
A typical reciprocating compressor for home or industrial use will contain one or more pistons in one or more cylinders.
An electric motor (or diesel, gas, propane etc.) will provide the energy to turn a crankshaft inside the compressor pump that causes the cylinder(s) inside it to move up and down, or side to side. In other words, the pistons will reciprocate.
As one piston rises it drives the volume of uncompressed air trapped above the piston, through a high-pressure valve, into a compressor receiver or air tank.
Immediately upon compressor start up, the pressure in the tank starts to rise. Free air is being compressed into the tank.
On the piston return stroke the high-pressure valve closes, and an intake valve opens. This allows the compressor to pull in free air into the cylinder.
The piston inside the cylinder rises squishing the air in the cylinder. This rise in pressure forces the intake valve to close and drives the now-trapped air through the high-pressure valve into the receiver. When this happens enough times, the volume of air being forced into a closed container – the compressor tank – causes the pressure in the tank to rise.
In case you were not aware, squishing is a highly technical term for us fluid power people!
Examples and diagrams show the piston in a vertical upright position. Within the huge makes and models of reciprocating air compressors in use and available in the market, a variety of piston orientations will be found. Small air compressors, for example, often have a horizontal piston. The orientation doesn’t seem to make any difference to the operation of the reciprocating air compressor. Since this process is a reciprocating one the name Reciprocating Air Compressor is the common name for the compressor that compresses air in this fashion.
I use the term receiver, air tank, air vessel and air hog interchangeably since are all tanks into which air is compressed or stored.
As long as the compressor motor is running, the piston(s) will keep reciprocating and driving air into the receiver, increasing the pressure in there to the cut out pressure level. when the tank pressure reaches the pressure switch cut out pressure level, the compressor motor will stop.
Features & Comments About Reciprocating Compressors
The size of the cylinder(s) on the reciprocating compressor, the number of cylinders, whether it is a two-stage compressor, or double acting compressor, really only have a bearing on whether that particular style provides you the compressed air flow in CFM that you need, and provides that air flow at the pressure you need.
A two-stage air compressor is one that has at least two cylinders. The first provides preliminary air compression and drives the pre-compressed air into the next cylinder which compresses the air from the first stage to an even higher pressure before sending the air into the receiver.
When a compressor has more than two-stages, i.e.: a two-stage, double acting unit, or a two-stage 4-cylinder unit, you might hear it referred to as a multi-stage air compressor.
A double acting reciprocating air compressor is one that has a cylinder that ingests free air and compresses that air in both directions, thereby delivering a higher volume of compressed air with each piston cycle than a single stage compressor could.
Regardless of how a particular air compressor is named, you need to know what your air flow and pressure demand is.
Knowing your air flow and compressed air pressure requirements will help you determine what the horsepower of the compressor you will need is because…
1 HP Motor Size = approximately 3-4 CFM at about 90 PSI
Once you know the approximate horsepower that you need to deliver your compressed air requirements,, you can start finding the best value compressor that fills those most important criteria.
Reciprocating Compressor – Best Value?
Best value is subjective, of course. Does it mean in purchase price, a compressor with the lowest energy cost to operate, or the lowest longer term maintenance costs?
The intended use for your reciprocating compressor will help answer these questions. The person seeking a high-capacity air compressor to run a plant will have different priorities over the home, do-it-yourself perspm, wanting a little compressed air to blow dust from a woodworking project, to fill a couple of tires, or driving a brad nailer.
I believe that reciprocating compressors up to the 15 hp size offer the best value in terms of purchase cost. Please see the page on this site about compressor costs for more information about that subject.
Did you know that…
If you purchase a belt-driven reciprocating air compressor check the compressor’s v-belts for proper tightness. Loose drive belts slip which reduces your compressor’s operating efficiency and wastes energy and your money!