We recommend the use of restriction gauges as an integral part of a preventive maintenance program. Air restriction gauges measure the amount of vacuum created when the air is pulled through the filter — measuring the build-up of dirt from a new filter’s installation throughout its useful life.

Using a restriction gauge maximises filter service life and prevents excess fuel usage from overly restricted filters, thus saving on operational costs. As a filter traps dirt, it becomes more difficult for the air to pass through the filter, and restriction increases in the air induction system. Air filter restriction may also be affected by high humidity or rainy conditions. As the air filter nears the end of its service life, filter restriction will increase more rapidly.

The restriction gauge should be calibrated per engine or vehicle manufacturer’s recommendations. The restriction gauge should be reset whenever the service indicator is checked to determine air filter restriction or when a new air filter is installed. If the air filter is not replaced, the position indicator will return to the same reading when the vehicle is driven under normal driving conditions.

If you’re not currently using a restriction gauge, you might consider adding one of the following air filter restriction gauges to your equipment.

Dash Mount Air Filter Restriction Gauge
The AFG30 mounts in the dash (2 1/16″ (52mm) diameter hole) and shows both inches and centimeters of column vacuum. A Murphy switch gauge shows the exact degree of air filter restriction at a glance.



Remote Mount Air Filter Restriction Gauge
The AFG37R mounts on the instrument panel or firewall and maintains the highest reading until the gauge is reset — enabling the gauge to be monitored whether the engine is running or not.



AFG38D – Direct Mount Air Filter Restriction Gauge
The AFG38D mounts directly on the air intake system and maintains the highest reading until the gauge is reset — enabling the gauge to be monitored whether the engine is running or not.



3900070920 – Digital Restriction Monitor
This air filter monitor is perfect for farm or truck operators and will let the operator know the health of the air filter.  No more waiting for your truck / Machine to turn into a slug, you will know when to change from the comfort of the cab. Comes with Dash Mount Indicator, Sensor, Sensor wiring, Instruction Booklet. May require P100089 fitting if your housing does not have one