[Brock]

You install it on the air intake tube. The engine sucks air through that line creating a certain amount of a vacuum. As the filter gets clogged the amount of vacuum increases and the gauge will read higher and higher until it reaches the red line and replacement is required. I don’t know if anyone knows that the correct readings are when the filter is new or at what reading the filter should be replaced as I have never seen one that comes from Prevost or Detroit.

[Ronald]

I have installed one of those on each of my coaches. As was mentioned above the gauge measures vacuum and as the air filter gets dirty the vacuum occurs between the filter and the turbo air intake.

Despite having the gauge I have never seen it get anywhere near the red mark because after 25,000 or 30,000 miles on the air filter I feel guilty and change the filter, despite the fact it probably did not need to be changed.

It is a good device to have however because I used to change air filters much too often. I probably still do, but to a lesser extent.

[Ronald]

Thanks this picture is from my bus