Can't adjust regulator on Compressor below tank pressure

[barryvabeach]

I can't adjust the regulator to have the downstream pressure lower than the tank pressure.  As I try to turn the downstream pressure down, the tank pressure drops, even with nothing connected.  Not just a little hiss, it is kicking out air, then when it gets below the starting pressure, the compressor kicks on and both pressure gauges start to climb.  Back story, it is a   25 gallon, horizontal tank Porter Cable compressor.  Bought it new many years ago, and always set the regulator  to 100 psi, used it primarily for spraying, and used a second regulator at the other end where it connected to the gun.  Now I have a new tool and it says the regulator should be adjusted to 60 psi.  When I try to do that , the knob starts to hiss, but then the tank volume starts to drop, and the compressor kicks in.  At first I  thought the regulator gauge may be bad, but I put another gauge at the end of the hose and triggered it, and it seems that even when the knob is way turned down, the air pressure at the end of the hose is still 75 psi.   AFAIR,  it has always been like this. 

Does it sound like time for a new regulator, or it is possible I just assembled it wrong?  From right to left, pressure switch with pressure dial, then regulator with dial above. 

       When I look at the back side of the regulator body, there is a port with a plug.   According to toolpartsdirect it is a 4 port P2 H regulator, whatever that means, that is discontinued and obsolete, no replacement.



After I posted it,   I realized I could have installed it backwards, but this bottom photo from the back side,  downstream is to the right, compressor is to the left, and it has a triangle pointing to the right where the output is

[barryvabeach]

Bad regulator,  bought a new one, everything works fine.

[MstrCarpenter]

Barry, I just saw your post on what you discovered about your regulator. Some regulators (but not all) will drain off the excess air as you lower the line pressure. I suspect it was debris or a leaking diaphragm.

[barryvabeach]

Barry, I just saw your post on what you discovered about your regulator. Some regulators (but not all) will drain off the excess air as you lower the line pressure. I suspect it was debris or a leaking diaphragm.

Thanks,  a leaking diaphragm was probably the issue.  New one works great.  When you lower it ,  it gives off a light hiss, the old one was not a light hiss at all, it drained off the tank.

[EricU]

They always go bad at an inconvenient time.

I wonder if that old one failed because it wanted to be upright.