A Guide to Diesel Engine Air Compressors

Air compressors have many diverse applications, used in industries including construction, manufacturing, shipping and utilities. They are also vital components in diesel truck, bus, coach and marine engines. In this short guide, we cover the role of air compressors in diesel engines, the different types of air compressors, and how to tell when air compressors need repairing or replacing. Read on for more information about air compressor parts and repair.

Simply put, an air compressor forces air from the atmosphere into very small tanks, reducing its volume and increasing its pressure. This pressurised air is stored for later use, either for the air brakes, air suspension system, pneumatic gear shifters or exhaust system. The air compressor should not be confused with the air conditioning compressor, which pumps a chemical refrigerant through a closed loop to produce cold air for the cabin of the vehicle.

Air compressors work in two different ways: through dynamic displacement or positive displacement. Dynamic displacement involves the compressor converting kinetic energy into static energy as air is pushed in and held in place to create pressure. Positive displacement refers to the process by which a compressor stores and slowly compresses air in a cavity, thereby increasing the pressure and potential energy.

Air compressors in diesel engines are otherwise categorised more narrowly based on:

Reciprocating compressors, which use positive displacement, are the most commonly used in diesel engines. They are either engine-driven or motor-driven.

It’s very important to keep an eye on air compressors in diesel engines; when they age and begin to fail, they affect the entire vehicle. Performing the following simple checks on your air compressor while you are completing its weekly clean can give a clear indication of whether it needs reconditioning:

1. Oil in the air lines
This is the biggest sign that it’s time to recondition your air compressor. When the piston rings or cylinder walls inside the compressor wear down, oil leaks past and into the air lines. If you see oil instead of water when you drain the wet tank, the compressor may be faulty.

2. Metal in the oil
If you notice metal fragments in your oil, it might be because compressor components have snapped, causing metal parts to grind against each other. This problem needs to be addressed immediately to prevent shards from travelling to the oil pan and scarring the main bearings.

3. Performance issues
Another common sign is that the air tanks take too long to fill or the air brake system pressure fails to reach 120 pounds per square inch (PSI). Otherwise, the compressor may be defective if it runs continuously and fails to cut out, or if there is no or low air pressure.

4. Excessive noise
If your air compressor is vibrating excessively, the bearings may be damaged and preventing the part from working properly. Other unusual noises like knocking or rattling, especially in a vehicle under load, indicate broken or loose internal parts.

5. Overheating
Signs of the cooler failing, as shown by increasing internal compressor temperatures, also point towards a malfunction. If the air is too hot or triggers thermal shutdowns, it may be due to restricted ventilation, a blocked oil return line or a clogged air filter.

A reconditioned air compressor will have your diesel engine feeling as good as new. As long as it’s properly measured, fitted and tested, as all parts are at Foxwood Diesel, your air compressor should keep you on the road well into the foreseeable future.

If you are currently experiencing any diesel engine issues and feel parts may need reconditioning, then please contact Foxwood Diesel today. We salvage, recondition and distribute spare parts for all major diesel vehicle manufacturers, including air compressors.

We have a wide range of online air compressor parts available for same-day dispatch across the UK, as well as a dedicated team with over 70 years’ collective automotive and engineering experience, specialising in the remanufacture of select diesel engines.

So that we can quickly find your perfect solution, please tell us your engine number when you get in touch to ask about our services. Or, for more insights into diesel engines, check out our blog.