The importance of safety filters

In October 2023, Product Profile3 MinutesBy NZ Trucking magazineNovember 18, 2023

Air is a critical component of combustion for a diesel engine. An air filtration system is designed to keep the engine intake air as clean as possible by removing particulate matter or debris. If the air reaching the engine is not clean, the engine will lose efficiency and have a shorter life.

Donaldson air filters deliver superior protection for heavy-duty off-road and on-road equipment. They are designed to withstand harsh environments and are ideal for all heavy-duty applications, from four-wheel drives to trucks and earthmoving equipment.

The filters are designed to provide effective, consistent performance over an engine’s life. They feature superior seal technology and a vibration-resistant interface, which helps to protect the engine and give it the clean filtered air it needs to perform.

Many Donaldson air cleaners contain two filters. The larger is known as the outer or primary filter. The role of the primary filter is to capture and retain contaminants from the incoming air, providing essential engine protection.

Many housings designed for off-road or high-dust environments often incorporate a smaller filter installed inside or, sometimes after, the larger primary filter. This smaller filter is often referred to as a secondary or inner filter or a safety filter.

The safety filter has two functions, to remain positioned and protect the engine from contaminants dislodged during routine primary element servicing, and to act as a backup if the primary element has been damaged before installation or incorrectly fitted.

Many air filter housings designed for low dust or highway vehicle applications do not include safety elements. While safety elements are not essential in low dust environments, extra care should be taken during routine servicing.

Engines should never be operated with just a safety filter installed.


While new air filters provide good engine protection, an air filter that has spent time in service and has built up a dust loading is even more efficient. An air filter will continue to provide cleaner and cleaner air throughout its usable service life.

Over-servicing can sometimes stem from a ‘better safe than sorry’ attitude, which may also achieve a ‘killing your engines with kindness’ result. Prematurely servicing an air filter means the media never achieves optimal efficiency and repeatedly allows excessive amounts of contamination directly into the engine.

Over-servicing impacts can be subtle but costly: higher-than-ideal oil burns, premature loss of performance and consistent failure to achieve OEM-published engine life.

Donaldson air filter indicators maximise filter life through various restriction measuring devices that help you get maximum filter utilisation and the greatest engine protection.

Donaldson is a leading manufacturer of filtration solutions for on-road and off-road heavy-duty trucks, working vehicles and agricultural machinery. Contact your local NAPA Auto Parts or Repco store for more information on Donaldson filters.