F-R-L and oil-mist-free main air line

by Julian Kulowski
(Warsaw, Poland)

Dear Mr. Bill,


I have an oil-mist-free main air line (for paint booth). Now I’m thinking to add a side air line with F-R-L for lubricating tools, but I'm not sure if it is absolutely safe for upstream / main air line? I don't want any oil at main stream. Maybe I need some kind of check valve?

Thank you in advance for an answer.

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Jun 07, 2017
oil-mist-free
by: Doug in s.d.ca.

Or maybe a diverter arrangement, if you use one or the other, but not both.

Or maybe just squirt a couple of drops in your tools directly, depending on how long you use use them at a time.

Jun 07, 2017
Oil moving upstream
by: Bill

Hello Julian.

The only way that air would flow backwards to your main line is if the air downstream from the FRL became a higher pressure than the main line.

Even if that were to happen, the over pressure should vent out the relieving hole on the regulator.

However, if no oil in the main line is critical, why take the chance?

Sure, put a check valve in the line to the FRL so that no back flow can occur. Just make sure it's sized large enough for the flow.

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