Splash and Pressure Lubrication Systems in Piston Compressors

March 2, 2017

7 minutes

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.

Splash Lubrication Systems

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.

How splash lubrication systems work: a closer look

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 Systems

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.

Splash lubrication systems vs. pressure lubrication systems: which is right for you?

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!

Frequently asked questions

What is a splash lubrication system and how does it work?

A splash lubrication system is a lubrication method used in piston compressors, small engines, and other machinery where moving parts, such as the crankshaft, cylinders, bearings, and gears, are lubricated by oil being splashed or thrown onto their surfaces. As the crankshaft rotates, dippers attached to the connecting-rod bearing caps pass through an oil reservoir at the base of the engine or pump, flinging oil droplets across critical components. This process reduces friction, minimizes wear, and helps dissipate some of the heat generated during operation. Splash lubrication is commonly found in smaller, simpler equipment where a cost effective lubrication solution is preferred over more advanced systems.

Where are splash lubrication systems commonly used?

Splash lubrication systems are commonly used in small engines, compressors, generators, motorcycles, and certain types of industrial equipment where simplicity and low cost are priorities. They are well suited for applications that operate at relatively consistent speeds and do not require the precision oil delivery that more advanced systems provide. While pressure lubrication has become the standard in modern engines and larger industrial machinery, splash lubrication remains a reliable and practical method for lighter duty applications.

What is the difference between splash lubrication and pressure lubrication?

The key difference between splash lubrication and pressure lubrication lies in how oil is delivered to critical components. In a splash lubrication system, oil is distributed by the mechanical action of rotating parts passing through an oil bath or reservoir, relying on gravity and motion to coat surfaces. In a pressure lubrication system, a dedicated oil pump actively forces oil through an oil filter and into precisely targeted areas of the compressor or engine. Pressure lubrication offers greater control, consistency, and reliability, especially under extreme conditions or at varying speeds, while splash lubrication is simpler and more cost effective for smaller applications.

What are the advantages of splash lubrication systems?

One advantage of splash lubrication systems is their simplicity. Because they rely on the natural rotation of the crankshaft to distribute oil rather than a dedicated oil pump, there are fewer components to maintain or replace. This makes them a cost effective lubrication method with lower upfront costs and straightforward maintenance requirements. Their ability to lubricate moving parts, including cylinders, bearings, and gears — without complex supporting systems makes them a practical choice for small engines, compressors, and generators where operational demands are moderate.

What are the limitations of splash lubrication systems?

The primary limitation of splash lubrication systems is their lack of precision. Because oil distribution depends on rotational motion and gravity, it can be inconsistent, some components may receive too much lubricant while others receive too little. This becomes especially problematic at low-speed operation, where reduced crankshaft rotation limits how effectively oil is splashed across critical components. Splash lubrication systems also struggle in extreme conditions, such as very high temperatures or heavy-duty continuous operation, where more advanced systems with dedicated oil pumps and filtration are better suited to maintain adequate lubrication and cooling.

How does oil viscosity affect splash lubrication systems?

Oil viscosity is particularly critical in splash lubrication systems. The lubricant must be thick enough to cling to the dippers and coat moving parts effectively, but not so viscous that it resists being splashed and generates excessive heat as it churns through the oil reservoir. Unlike pressure lubrication systems, where an oil pump can transfer oil regardless of its consistency — splash lubrication systems rely entirely on the physical properties of the oil to perform. Using the wrong viscosity can compromise the system's ability to lubricate cylinders, bearings, and other components, leading to increased friction, accelerated wear, and reduced compressor performance.

How do splash lubrication systems contribute to the longevity of a compressor?

When properly maintained, splash lubrication systems can extend the service life of a compressor by continuously reducing friction between moving parts, helping to dissipate heat generated during compression cycles, and protecting critical surfaces from wear and tear. The key to longevity in a splash lubricated system is diligent maintenance, keeping oil at the correct level, monitoring viscosity, and ensuring oil purity through regular filtering and replenishment. Neglecting these steps can quickly undermine the system's ability to protect components, shortening the compressor's operational lifespan and increasing long-term costs.

Can splash lubrication systems handle varying environmental conditions?

Splash lubrication systems are best suited for stable, controlled environments. Significant changes in environmental conditions, such as fluctuating temperatures, high humidity, or dusty surroundings — can affect oil viscosity, oil purity, and the overall efficiency of the lubrication process. In harsher or more variable environments, the oil may degrade faster, requiring more frequent changes and closer monitoring. For applications where environmental conditions vary widely or unpredictably, pressure lubrication systems with dedicated filtration offer greater durability and reliability, as they are better equipped to maintain consistent oil delivery regardless of external factors.

How does oil mist lubrication compare to splash lubrication?

Oil mist lubrication is a more advanced method that disperses a fine mist of lubricant throughout a system using an air stream, ensuring that even hard-to-reach components receive consistent coverage. Compared to splash lubrication systems, oil mist offers more uniform distribution and is particularly effective for high-speed machinery and industrial equipment where splash lubrication may not reach all critical components reliably. However, oil mist systems are more complex and costly to implement and maintain. For most piston compressors and small engines, splash lubrication remains a practical and suitable method, while oil mist is more commonly reserved for specialized industrial machinery.

What maintenance does a splash lubrication system require to operate efficiently?

To operate efficiently and reliably, a splash lubrication system requires regular attention to three key areas: oil level, oil quality, and oil viscosity. The oil reservoir must be kept at the correct level at all times, too little oil means critical components like bearings, cylinders, and gears may not receive adequate lubrication, while too much can cause hydraulic lock and excessive heat buildup. Oil should be filtered regularly to remove contaminants and replenished when necessary to maintain its lubricating properties. Checking and maintaining the correct oil viscosity for your operating conditions is equally important, as the wrong viscosity reduces the system's efficiency and increases wear on moving parts. Following the manufacturer's recommended maintenance schedule is the most reliable way to protect your compressor and maximize its performance and durability.