EC12 fills to 125, stops but bleeds off to start pressure but wont fire up.

This can happen at different times, works great other times. I think it is the non return valve (item 53)


Hitachi EC12 air compressor

Hitachi EC12 air compressor Photo:


Is it a leak?
by: Doug in

Yeah, that’s what we usually call a check valve. Given that this is an intermittent problem, there’s probably some crud inside near the seat.

You can probably take it out and disassemble, clean, and re-assemble it and reinstall. (maybe even just blow it out if you want to try that first) And do be sure the tank is not under pressure when you do the removal!

If that doesn’t do it, then you can replace it.

Have fun.

And another Hitachi EC 12 that is bogging down and not running

by: Peter

Hi this Peter .

I have a Hitachi EC 12 twin bogging down not running.

I checked capacitor,replaced with capacitor made by Packard, model Prcf40 40ufd :5. 440vac 60/50hz from the local a/c store.

The original is made by Facon mod 7G73400P7B 40 uF: 5 SH. 450 Vac cl.D 50Hz .

But it doesn’t work either.

You think I should install the OMD so it can works .

The capacitor from Hitachi is so expensive $38 a each or you think just keep the money and by a new compressor?

It is ten years old. I want to make sure it work before order the capacitors .

Thank you

Peter, are you sure it is the cap? How did you test it, please?

When you acquired the replacement, did you take the old one and ask the store person to give you the exact replacement?

If you don’t have the same specs on the replacement capacitor, or if you haven’t checked the old cap (you say you did, but how?) then it may not even be the cap that’s at fault. Need a bit more info on that? Right here.

At what pressure is your compressor bogging down? Is it at the same pressure every time, or does that vary? What is the circuit amperage? Are you using an extension cord? (Don’t) With the intake filter removed, do you still get the same issue?

There are a host of things, including a cap problem, that can cause a compressor to bog down.

Another Hitachi EC12 pressure switch is releasing air at cut-out pressure

by BBB

I have a Hitachi EC12.

The existing pressure switch was a MDR 21(?) 4 port switch.

That one had the symptom of setting off the safety valve at the cut-out pressure (~125 psi).

The valve was rated at 10 bar (~145 psi), so I’m assuming there was some mechanical method to cause the valve to release or it was faulty.

I’ve replaced the pressure switch (with and the valve. I think I’ve installed everything properly, but now, the pressure switch stops the motor at the cut-out pressure (~120) and releases air through the back of the switch (the safety valve appears closed).

Just wondering if that rings a bell with anyone. I don’t think there’s an issue with the safety valve, unloader tube, etc. because the tank is able to reach “max” pressure with any apparent leaks. It appears like the switch itself is releasing the air pressure once it reaches the cut-out pressure.


Hitachi pressure switch leaking
by: Bill

Well BBB, I don’t believe you have a problem with the pressure switch, based on what you have written.

I think you have a problem with your tank check valve.

The pressure switch you acquired has an internal unloader I believe, which opens when the pressure switch reaches cut out and trips off.

If the tank check valve is failing / leaking, air from the tank will exhaust through the unloader valve inside the pressure switch until the tank pressure reaches cut in, and then your air compressor will start again.

See the pages on Check Valves and Unloader Valves on this site for more info about how these two work together.


Thanks for the quick reply
by: BBB


After reading some more on your very informative site, I believe you are correct. I will replace the CV and keep my fingers crossed that nothing else breaks down.

I, for one, appreciate the fact that you are taking the time, effort, and expense of running this website and providing free advice to readers. [I’m sure your karma account is growing instead.]


You are welcome, BBB. Karma?
by: Bill

More good Karma can only be a positive, yes?

Lots of folks contribute freely of their time and expertise on the air compressor help site, so I’ll pass on some good Karma thoughts to them too.

Not sure what Karma is? I totally wasn’t either so I read up on it here:, in case you have any interest.