Two of the most popular air compressor configurations are the piston type or reciprocating and rotary screw compressors. There are a few factors that set the two apart based on the way in which they have been set up and the method employed to compress air.
Let us start with piston or reciprocating air compressors. These are easily the most commonly used air compressors across the world. They run on the same mechanical principle as the combustion engine. A crank that turns a connecting rod, which in turn moves the piston up and down inside the cylinder head. The inlet valve lets air into the cylinder when the piston is in its lowermost position, the latter is then driven upward to compress the air, converting electric energy to kinetic energy in the process. A typical piston air compressor is oil-cooled, that results in the release of oil residue when the compressed air is discharged.
Rotary air compressors, on the other hand, are typically configured with two interlocking helical rotors fit with a small gap between them and soaked in an oil bath inside a housing. The inlet valve lets air in, which is compressed in the space between the screws when they turn, reducing the volume and increasing the pressure.
There are oil-free rotary screw air compressors available as well. In fact, there are some air compressors that even come equipped with just one screw, but again, these are not very common.
Here we have a list of factors compared which will let you determine which of the two types of compressors might suit your needs better.
Rotary air compressors and piston compressors - Comparison
- Maintenance and wear and tear – In piston compressors, the wear and tear is greater due to a large number of moving parts. This results in more maintenance compared to a rotary screw processor. However, because of the simple mechanical setup of a piston compressor, it is easier to maintain and fix, despite the greater frequency of maintenance required.
- Operating temperature, noise and vibration – Typically, a rotary compressor has lower operating temperatures than piston compressors. Friction is the lead cause for this, because the rotors in the screw compressor don’t come in contact, whereas piston rings are in constant contact with the cylinder walls, creating greater friction and raising temperatures. The former also generates less noise and vibrates lesser than the latter due to the same reason.
- Air flow and operation time – Because of the high temperatures in a piston type compressor, it cannot be run non-stop due to the risk of overheating. Furthermore it is also typically run at only 50% of its total CFM or air flow capacity. The rotary screw compressor, however, is capable of being run continuously. You can also purchase a rotary screw compressor that is rated as close as possible to your required air flow capacity rather than one rated at double the capacity.
- Space required and energy efficiency – Since rotary screws are encased next to one another in one chamber, the whole setup usually takes up less space than a piston compressor which requires cylinder heads for the vertical movement of the pistons. The former are also more energy efficient than the latter with fewer transmission losses as well. However, the effects are only discernable in compressors of 20 HP or more horsepower.
- Pressure ratio and volume – The compression range is much greater on a piston configuration when compared to a rotary screw type. There is also more flexibility in terms of pressure ratio and capacity. However, in rotary compressors, while the flexibility is limited, the comparative volume capacity is much greater than that of reciprocating air compressors.
- Oil carry-over – Piston compressors typically discharge more oil into the stream of compressed air than rotary screw compressors do. Due to the high-friction moving parts, wear-and-tear leads to more oil carry-over than in rotary screw compressors.
- Price – Due to the above mentioned factors, the cost of a piston compressor is a lot lesser than that of a rotary screw compressor.
Now that you know the major differences between the two type of compressors – piston and rotary, and what advantages and disadvantages either brings to the table, you can make an informed investment. Before you decide either way, make sure to check out some great deals and one of the widest ranges of compressors available at our online store. If you have more questions, our air compressor experts at Compressor World will be more than happy to help you out.