by Daniel
(Windsor, Ontario)

Using a DeVilbiss Pro 4000 compressor, with a pressure switch that causes the compressor to kick in whenever the pressure drops to roughly 95 psi ( and to cut off at about 130 psi). That pressurized air runs into a Numatics P21B04 pressure regulator.

Devilbiss Prof 4000 air compressor
Devilbiss Prof 4000 air compressor

Whenever I dial that regulator down to provide a lower pressure to my tool … let’s say, down to 60 PSI … I hear a hiss of air (as the pressure drops). My spouse perceives this as a malfunction, and tells me that the regulator didn’t used to hiss like that.

Something else about the operation of the regulator that doesn’t seem right to me: I would think that adjusting the knob for lower downstream pressure would have immediate results … that I would see the pressure indicator move as I adjust the control knob. This is not the case. Instead, turning the control know just seems to create an air leak that eventually stops when the contained pressure is sufficiently reduced.

Id we’re dealing with a malfunction, we’ll probably just replace the pressure regulator. But if this is how the unit is intended to function, I don’t want to spend $$$ and end up in the same situation.

What do you think? Does this sound like a malfunction?

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Compressor regulator malfunction
by: Bill

Nope. Your compressor regulator sounds like it is operating correctly, and when you dial the regulator pressure down, you will hear a hissing sound as the compressor relieves the downstream air.

“would see the pressure indicator move as I adjust the control knob” this is worrisome, as you should see the regulator gauge needle move as you dial down the pressure.

However, if you dial the pressure down to a new setting, and the regulator stabilizes at the new setting, and the regulator gauge displays that setting, then I wouldn’t change out the regulator.

You may just have a sluggish gauge as they do, over time, corrode and then fail.

See: https://about-air-compressors.com/understanding-compressor-air-regulators.html if you want a detailed understanding about all facets of compressed air regulators.

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