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

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My ec 12 compressor will run and shut off around 125 psi and then it bleeds off untill it turns on around 80 psi Ive replace the pressure switch and its still doing this Why?

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It souds like a sticky "non return valve". See the fix below.
The non return valve is the chrome part with a hex cap adjacent to the upper tank. Remove the cap and make sure the piston moves freely. Slight resistance is ok, but if it sticks your compressor willl continually blow off air.

The check valve or "non return valve", as listed in the Hitachi parts manual is definitely the culprit here, but there is an alternative solution to replacing the entire valve that was actually suggested to me by a Hitachi Tech when I stopped by my local service center to pick up a new non return valve. Obviously, the rubber piston swells and sticks to the point that the spring under the piston can't over come the friction. I removed the piston and carefully reduced its diameter, by hand, with varying grades of wet or dry paper and it now operates perfectly. If one is uncomfortable with such a repair, at least keep it in mind for a quick jobsite fix. I have now been running my repaired compressor for several months without issue.

Posted on Aug 23, 2010

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You probably need to spray some penetrant on the high pressure relief valve and turn the ring attached to to rotate the stem of the valve. Also called the pop off valve.

Posted on Jul 10, 2010

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