Question about Hitachi EC12 Portable Electric 2hp Air Compressor, Oil Lubricated

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My EC12 builds up pressure, but then releases all but about 10 psi.

The machine builds pressure fine, but when it reaches max (125 psi), it releases all but about 10 psi.  I initially thought that the spring loaded pressure relief valve had went bad, but the air comes out of the small hole in the brass fitting below and to the side of the relief valve.  I am not sure if this is a pressure sensor or not, but it has a small air hose from the tank the pressure switch.  Any ideas?

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  • Anonymous Oct 25, 2008

    Compressor runs normally and pressurized the two tanks.  When the pressure reaches the cutoff psi, the motor shuts down.  However, immediately after, a small hole in a brass fitting behind the pressure switch and fitted to a rubber hosing, starts to leak air at high velocity.  Pressure drops and quickly reaches the minimum set point.  At this point, the motor reengages and starts to re-charge the tanks.  This pattern continues and there seems to be no end.  

  • Anonymous Nov 12, 2008

    same

  • fc143 Nov 14, 2008

    My compressor is an Eaton that is just like the Hitachi, but it has oil in the compressor.
    My compressor (a portable) starts pumping when I turn it on. It goes up to 120 lbs and then at the point it is to shut off, it does. The air then starts escaping from the compressor switch and purges the tank down to 70 lbs; I believe that this is through the unloader which is built into the pressure switch. The compressor tries start up again, but fails and repeats this action until I shut the system down by pulling the plug because if I try to depress the on and off switch it lets more air out of the tanks. The pressure switch was replaced with a new one, but this did absolutely no good, it keeps doing the same thing.

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The non-return valve is sticking and it's an easy fix. First, for safety, unplug the electric power to the unit and release any pressure in the tanks. Then unscrew the cap of the non-return valve (between the compressor and the tanks). Inside you should find a tapered rubber plug which is probably sticking in the valve housing. Sand down the diameter of the large end of the plug, being careful not to damage the flat face at the narrow end (which is the sealing surface). For sanding try 400 or 600 grade wet-or-dry paper and sand until the plug just moves freely in the housing. Reassemble and the compressor should work. Incidentally it's an oil-type unit, and quite durable. Make sure it has enough oil.

Posted on Nov 14, 2008

  • Aldude
    Aldude Nov 26, 2013

    Thanks, it worked for me. Here is a picture of where things are.

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Bruno2

Thanks for the solution! Worked like a charm!

Posted on Mar 12, 2009

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Bruno2

This was a great find, been having this problem for a while, but your suggestion worked. Thanks so much.

twodogs2

Posted on Nov 22, 2008

ACORDING TO THE MANUFACTURES SPECS ON THIS MODEL COMPRESSOR IT HAS AN OIL SPLASH SYSTEM AND I KEEP SEEING IT REFERED AS A CHEAP OILESS COMPRESSOR...IM TRYING TO DECIDE WHAT ONE TO BUY BUT NOBODY SEEMS TO KNOW WHATS WHAT AND NOW NOT SURE IF I WANT ONE OF THESE...

Posted on Oct 08, 2008

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Yes, this is normal.

It is a safety valve.

1.)
Someone turned up the max pressure adjustment past the 125 psi limit.

Readjust back down to about 110 psi.

2.)
If it releases all the pressure after it kicks off (after building max pressure), then this is quite a common symptom of cheap oil-less compressors.
From your description you have a cheap oil-less compressor.

Posted on Oct 07, 2008

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