Question about Racor RK19671 Vacuum Gauge

[mainemandean]

I just installed a Racor RK19671 Vacuum Gauge on the top of my filter/separator. The instructions say to to open up the time blue cap on top when installing. I did that. But am I now supposed to close it back up? I did not. Then I ran the engine briefly, and it showed no vacuum at at all. The gauge and filter/separator are on the vacuum side of the pump.

See the fourth photo on this page. (Oddly the first pic does not show it, but mine has it.)

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[jamhass]

A clean filter will, in my experience, show no vacuum on the gauge. Vacuum will build as the filter clogs, and a rapid rise in vacuum is a warning sign that it is time to replace filters.

By the way. Is your gauge a "drag pointer" type? If so, the pointer will be left at the highest vacuum achieved, letting you know that data without being next to the engine an full tilt. If not, you might want to check the vacuum under high load/rpm conditions on occasion (or replace with a drag pointer type).

[mainemandean]

Thanks, Jamhass.

Someone told me to leave that little cap open forever. Do you concur with that?

I have a telltale pointer on the gauge, which shows me its highest point reached, and stays there until I reset it. It even has a third needle, which one can set at a pressure one determines to be a "red line."