Piston compressors have been around for centuries. They can be either oil-injected or oil-free, depending on the application and end use. In oil-injected models, the oil typically serves three crucial purposes: cooling, sealing and lubricating. But not all oil-injected piston compressors lubricate components the same way. There are two common systems for lubricating the pump in piston compressors: splash and pressure lubrication.
In splash lubrication systems, oil is applied to the cylinders and pistons by rotating dippers on the connecting-rod bearing caps. Each time they rotate, the dippers pass through an oil-filled trough. After running through the oil trough, the dippers splash oil onto the cylinders and pistons to lubricate them.
While splash lubrication is effective for smaller engines and pumps, it’s not a precise process. Parts of the pump may be insufficiently oiled or oiled too much. The amount of oil in the trough is vital for proper operation. If there is not enough oil, wear between critical components may occur, and too much oil will cause excessive lubrication, which can lead to hydraulic lock.
The type of oil used, and its viscosity is also important in a splash lube system. The oil must be thick enough to provide sufficient lubrication and cling to the dippers, but not so viscous that it heats up as it is churned about in the oil trough. Oil purity is also critical; oil should be filtered regularly and replenished when necessary.
Splash lubrication systems operate on a straightforward mechanical principle, there are no pumps, sensors, or complex components involved. As the crankshaft rotates during compressor operation, the dippers attached to the connecting-rod bearing caps continuously scoop through the oil reservoir at the bottom of the crankcase. This motion flings oil droplets throughout the interior of the compressor, coating the cylinder walls, pistons, bearings, and other moving components with a thin film of lubricant.
Because splash lubrication systems rely entirely on the rotational motion of the crankshaft to distribute oil, they are most effective at consistent operating speeds. Intermittent or low-speed operation can reduce the effectiveness of oil distribution, as slower rotation means less oil is being splashed across critical components. This is one of the key reasons splash lubrication systems are best suited for smaller, single-stage piston compressors that operate at relatively steady speeds and lower pressures.
One of the primary advantages of splash lubrication systems is their simplicity. With fewer moving parts and no dedicated oil pump required, splash lubricated compressors tend to have lower upfront costs and are easier to maintain. However, this simplicity comes with trade-offs, the lack of precision in oil delivery means that regular monitoring of oil levels is essential to ensure all components are receiving adequate lubrication at all times.
Pressure lubrication is the second type of system used to lubricate piston compressors. It is a more technically advanced and usually more costly method, but it results in longer life for a compressed air system.
Pressure lubrication is a process where an oil pump precisely distributes oil to key areas of the pump. Typically, the oil is pumped through an oil filter and into the pump where it is then recycled and reused; using a replaceable oil filter can further improve the life of the oil. The oil is transported to the key area by use of an oil pump. Therefore, the viscosity of the oil is not as critical as with a splash tube system.
Either method has been used extensively in many various pump and engine applications, and both are suitable for piston compressor applications. When purchasing a new piston compressor, decide what’s important for you. If upfront cost is important, a splash lubricated compressor may be the way to go. But if you are willing to invest more in a pressure lubricated piston compressor, you’ll be rewarded with added longevity and reliability.
When comparing splash lubrication systems to pressure lubrication systems, the right choice ultimately comes down to your application, budget, and long-term operational goals. Here's a quick summary to help guide your decision:
Splash lubrication systems are a good fit if you are running a smaller piston compressor for light to moderate duty applications, have a tighter upfront budget, and are comfortable with routine oil level monitoring and maintenance. They are reliable and time-tested for the right applications, as long as oil levels and viscosity are kept in check.
Pressure lubrication systems are the better choice if you need a compressor for heavier duty or continuous operation, are prioritizing long-term reliability and component life, or are operating in conditions where consistent, precise oil delivery is critical. The higher initial investment tends to pay off over time through reduced wear, fewer maintenance interventions, and a longer overall service life.
If you're unsure which system best suits your needs, an Atlas Copco compressed air expert can help you evaluate your application and make the right call.
What kind of lubrication system does your piston compressor use? Let us know in the comments below and visit us at www.atlascopco.com/air-usa to learn more!