The problem is in the check valve where air enters the tank.when leaking it lets air pressure up to the air piston causing the motor to stall upon restart.replace check valve.average cost of part 15 to 30 dollars.simple fix
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.
I too have this problem, and it's interesting to see how many people have had this problem now I've done a search for it.
In my case the plunger in the valve is sticking. I can see it is, and it's failing to return, but I can't manage to remove the hex bolt opening on the non return valve to get at the plunger to trim it in size.
It's absolutely fused. I've tried every socket I have and every adjustable wrench. It just stays unmoved of slowly gouges the metal away. Any ideas? It's an older model I know. Was it possibly thread-locked on the earlier ones?
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Have same problem with EC12, air leak out, try to start, hums and blows circuit.Problem IS the Non-Return-Valve. Tried all your solutions, sanding, etc but only worked temporarily. Replace valve and all was fine. This is a great workhorse compressor, cast iron, recycles fast - but what LED to this problem? Answer is bleed tanks after use. Moisture alters the rubber to expand in the valve and stays sticky. Use non-detergent compressor oil. Has been known people use light motor oil and the inherit detergents also effect rubber and valve. Do not overfill, just invite problems you don't want, like bad relatives at your wedding drunk. Good practice bleeding tanks anyway - being cast iron, many rust at the bottom and leak. Rumor has it that newer tanks are inside teflon-coated.
If you are one who has an oil-less compressor, it's a throwaway, no matter how big it is. Pistons are plastic, burns out in a heartbeat. Longer to get to pressure and if read warranty carefully, it's only for the tank, shorter on electrical and few months on compressor. Money out the window and not worth repairing.
EC12 is a great cast iron workhorse with pistons like a car and portable. Take care of it. Hope this helps all of you who are trying to put a chicken on the table.
Hank - SF
SOURCE: My Hitachi EC12 builds pressure, shuts off, then air escapes
I have the same compressor with the same problem. I have temporarily eliminated the thermal reset with a piece of 12 gauge hard wire and it runs just fine. However, I do want to replace it before the warm weather come to the north. I tested the draw at 15.5 amps and the reset was a 17 amp. I am told by someone with superior electrical background that I need to install a 20 amp thermal reset in it's place. I have found that mine runs best when plugged directly into a 20 amp circuit and when using an extention cord I have a 10 guage cord that will carry the load needed to run the EC12. I have also changed to 100% synthetic oil.
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