No matter what system or method you use for determining air cleaner element service intervals, it should be geared around restriction measurements.
The element in the air cleaner should be serviced when the maximum allowable restriction, established by the engine manufacturer, has been reached.
The element should not be serviced on the basis of visual observation, because this will always lead to over-servicing.
Over-servicing can cause:
1. Element damage, due to excessive handling
2. Improper installation of element
3. Contaminated from dust
4. Increased service cost, time, and material.
Note: Points 1, 2 and 3 will cause shortened engine life.
What is restriction?
Restriction is the resistance to airflow through the air cleaner system into the engine.
What instruments do we use to measure restriction?
Restriction is best recorded by a water manometer, an air cleaner service indicator or a dial gauge calibrated in inches of water.
Since some users will not have a water manometer or dial gauge available, the use of permanently mounted service indicators should be considered.
The indicator should be mounted in a position where the operator can monitor the condition of the element constantly.
How are restrictions measured?
Accurate restrictions can only be measured at maximum airflow. On naturally aspirated or supercharged (not turbocharged) diesels, the maximum airflow occurs at maximum RPMs (high idle) without regard for engine power.
On turbocharged diesel engines (and gasoline and LPG engines) the maximum airflow occurs only at maximum engine horsepower at governed RPM.
Most engine manufacturers suggest a maximum allowable restriction of 20-30 inches (manometers are generally calibrated in inches) for diesels. Exceeding these maximums will affect engine performance.
The operator should not be alarmed when the signal on the restriction indicator begins to appear.
Air filter manufacturers design these service elements to withstand several times these recommended maximums without collapsing or leaking dirt into the engine.
Where are restrictions measured?
Restrictions are measured in the air cleaner outlet tap (if provided), at a tap in the air transfer tube, or within the engine intake manifold.
Measuring restriction in dry air cleaners
As a dry air cleaner element becomes loaded with dust, the vacuum on the `engine side` of the air cleaner (at the air cleaner outlet) increases.
This vacuum is generally measured as `restriction in inches of water`.
The engine manufacturer often places a maximum allowable limit on the amount of restriction the engine can withstand without loss of performance before the element must be serviced.
Mechanical gauges, warning devices, indicators, and water manometers are available to inform the operator when the air cleaner restriction reaches this recommendation limit.
These gauges and devices are generally reliable, but the water manometer is the most accurate and dependable.
To use a manometer, hold vertically and fill both legs approximately half full with water.
One of the upper ends is connected to the restriction tap on the outlet side of the air cleaner by means of a flexible hose. The other end is left open to atmosphere.
With the manometer held vertically and the engine drawing maximum air, the difference in the height of the water columns in the two legs, measured in inches, is the air cleaner restriction.
A restriction indicator’s “lock-up” restriction lon the indicator with your mouth. If the indicator locks up, it is okay, if not, replace indicator.troys your engine protection. Deeply embedded dirt is never released by tapping. It is always safer to keep operating until you can change to a fresh filter.