Most air compressors require oil to work. The oil works as a lubricant and coolant, protecting metal parts from wear and overheating. Proper lubrication is necessary to prevent noise and ensure a long service life for your tool.
However, not all oiled air compressors use the same type of oil. Depending on the generated heat and the required viscosity, the type of oil may change in one case or another. In this article you’ll know the different types of oil used in oiled air compressors.
With this new knowledge, you’ll be able to choose wisely a good replacement for the lubrication of your air compressor in case you don’t find the type of oil required.
What is Oiled Air Compressor?
As its name says, it’s an air compressor that uses oil as a lubricant. A suitable lubrication is necessary for the proper functioning of the bearings and running gear.
The lubrication system of an air compressor is formed by:
- Crankcase sump.
- Oil pump.
- Oil filter.
- Cylinder lubricator.
Here’s the step-by-step explanation of how it works:
- The oil remains inside the crankcase sump.
- Then, the oil pump sends oil from the crankcase sump to the strainer.
- The strainer prevents large particles from entering the filter.
- After that, the oil passes through the filter, losing the smallest dissolved particles.
- The filtered oil passes through a pressure-regulating valve to the cylinder and bearings.
- Finally, the oil returns to the crankcase sump.
There’s another lubrication method known as “splash lubrication”, where a dipper attached to the bottom of the piston rod dips into the oil and then spreads it on pistons and the bearings.
On the other hand, rotary compressors don’t use an oil pump during the lubrication process. Instead, they use differential pressure to move the oil from de crankcase sump to the moving parts. Before entering the pump, the oil passes through an oil cooler to reduce its temperature.
Air Compressor Oil Types
In order to extend the lifespan of your air compressor, you must know the oil type that your device needs and why. There are many lubricant options on the market, but not all of them are suitable for air compressors.
As a golden rule: Don’t use common motor lubricants on air compressors. Motor lubricants contain detergents and special additives to promote internal combustion. Additives tend to generate waste, shortening the life of oil filters on air compressors.
Therefore, it’s better to opt for air compressor oils. If you don’t find this type of lubricants, use a non-detergent blend. Using a lubricant different than the specified on the user manual could make you to lose the product warranty. So, think about this before making any decision.
You can use both mineral and synthetic lubricants on air compressors. Below, you’ll find a detailed explanation of each oil type.
It’s the type of lubricant derived form crude oil. According to the API, mineral oils are classified as:
- Group I with a SAE viscosity between 80-120. They contain less than 90% of saturates and more than 0.03% of sulfur.
- Group II with a SAE viscosity between 80-120. They contain more than 90% of saturates and less than 0.03% of sulfur.
- Group III with a SAE viscosity greater than 120. They contain more than 90% of saturates and less than 0.03% of sulfur.
- Group IV that includes all kinds of polyolefins.
- Group V that includes all mineral oils excluded from groups I, II, III and IV.
Standard mineral oils are suitable for light and medium duties. For those people who don’t use their air compressors so frequently. Usually, mineral blends are cheaper than synthetic ones.
It’s the type of lubricant derived from synthetic hydrocarbons, which are extracted from petroleum through complex chemical processes. The most common synthetic oils are:
- Multiply alkylated cyclopentanes.
- Ionic fluids.
- Silicate esters.
- Alkylated naphthalenes.
- Phosphate esters.
- Polyalkylene glycols.
- Synthetic esters.
Synthetic oils can maintain their viscosity at very high temperatures. This makes them suitable for heavy duties and long hours of work. They’re the best option for contractors and people who use their air compressors at least three times a week.
Synthetic blends also improve compressor air performance and reduce noise generation. However, they’re more expensive than mineral oils.
Now that you know what type of oil you should use in an air compressor, it’s convenient that you also know the required viscosity. Usually, for air compressors you need a SAE viscosity between 20-30.
The higher the number, the higher the viscosity. A SAE 20 viscosity is recommended for work at low temperatures. In winter, for example, you need less viscosity so the lubricant runs smoothly through the pump.
On the other hand, at very high temperatures, as it happens during summers, it’s better to opt for a SAE 30 viscosity. Lubricants tend to lose viscosity at high temperatures, losing their ability to form a thin layer on the moving parts.
A SAE 20 lubricant during a hot summer would become too liquid, increasing the risk of friction and overheating.
So, depending on the season, you must vary the type of oil you use to get maximum performance.
As you can see, the life of your air compressor doesn’t depend only on its design or the quality of its materials. It also depends on the type of lubricant you use. Always opt for the oil type recommended by the manufacturer. If you can’t find that kind of oil, look for other options with similar properties.
Never use motor oils on air compressors, because they generate too much waste that can affect the performance of moving parts. Always choose lubricants without additives.
Depending on the frequency of use and temperature, choose a suitable viscosity. If the viscosity isn’t sufficient, the risks of wear and overheating will be higher.
As a final recommendation, try to change the oil every three months in the case of reciprocating compressors or after seven thousand hours of work in the case of rotary devices. If you don’t use your air compressor so often, changing the oil once a year is more than enough.