Hitachi ec12 Compressor runs, and just before it shuts off at around 110 psi it blows oil out of the oil filler hole

by Jim
(Atlanta)

Compressor runs, and just before it shuts off at around 110 psi it blows oil out of the oil filler hole. This happens somewhat violently spraying the surrounding area with oil. The oil is also foamy. the tank holds pressure once I turn the compressor off. Any ideas what can cause this? Thanks.

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Bill says...

Jim, from what you are saying, I think you may have two problems... but one for sure.

If oil is coming out of your intake valve port, then that valve is leaking. It may not be enough to seriously slow down the tank fill up, but it is enough, when the pressure is getting to the 100+ PSI range, to allow compressed air out that valve instead of forcing all of the air into the tank.

As to the oil, I can't tell how much there is from your posting. Oil from the lube sump is always wicking up the cylinder walls as the piston reciprocates, and that is the oil that is being blown out of your intake when it reaches that cut out pressure level.

Some oil wicking and getting blown into the tank is normal. It blowing out the intake valve port is not. You decide if there is so much oil that maybe you need to check the piston seals?

But, get that valve checked out first.

Cheers,

Bill




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Hitachi ec12 Compressor runs, and just before it shuts off at around 110 psi it blows oil out of the oil filler hole

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Jun 24, 2011
 Good news addendum
by: Franz

Note: I used new rings when I reassembled the compressor, of course!
Jun 24, 2011
 Good news
by: Franz

Well, I pulled the head and cylinder off of my EC12. Sure enough, there were some scratches in the cylinder wall.

The cylinder diameter is about 2 inches. I honed the cylinder using a brake-cylinder hone that I refitted with longer honing stones. (The brake-cylinder hone can accommodate cylinder diameters from 1.25 to 2.75 inches, and the original stones were only about one inch long. I think that's too short to do an accurate hone on a cylinder this wide. I replaced those stones with longer (3-inch?) stones for a bigger hone.)

I honed first with 220-grit stones until the scratches were mostly gone. Then I honed for a couple of minutes with 400-grit stones. After that, I cleaned the cylinder with mild soap, then WD-40.

I oiled up the cylinder, reassembled it into the compressor, and ran it for 10 seconds with no load (bleed-valves open). Then I closed the bleed valves and ran it up to pressure. It worked great. No more blow-by!
May 31, 2011
 Any luck?
by: Franz

Howdy. Did you guys ever figure out what was happening with that compressor? I've got a Hitachi EC12 that blows a lot of air into the crankcase as it runs. As you described, it is enough to pop the oil filler plug out. Otherwise, the tanks reach pressure okay.

It sounds plausible that it could be having blow-by in the cylinder. I might have to pull it apart and use a cylinder hone on it, and replace the rings. I haven't done it yet.

Thanks.

Franz
Jan 07, 2011
 Hitachi ec12 blows oil
by: Jim

Hi Bill,

So your wife thinks you're cute huh. How's her eye site? Just wondering...

Any way, this pressure is entering the sump before shutoff. Just before. Shutoff should be around 125 psi and the "blowout" happens at 110 - 115 psi. When the oil releases, I turn the compressor off so I don't know if it would shut down on its own or not. I don't know if it is unloading properly or not. I do now that once I turn it off, the tank holds pressure so its ot the check valve. Tonight I'm going to re-examine the parts diagram and see if it makes any sense to me.

My thought was that possibly it was blowing past the rings. I haven't torn it down to inspect the cylinder wall or check for broken rings. Before I did I thought I'd see if you have any ideas.

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Jim, OK, so she wear glasses, ok?? And ya, they are pretty strong... and I don't have many lights on ... and ... well?

Your compressor problem is, though doubtless a giant pain in the a@@ for you, quite interesting for me, and the folks that are following this thread.

Maybe, with a plastic drop sheet or some such, let the compressor run and see if it will shut down on high pressure cut off? I think it will.

I also think that once the pressure reaches a certain point, it breaches (maybe the rings) a gasket or a seal, and allows higher pressure air into the sump, resulting in your symptoms.

Thanks for taking the time to update us on this.

I look forward to the next installment.

Bill
Jan 05, 2011
 Oil blows out the Oil Filler Hole
by: Jim

Hi Bill,

First, thanks for the quick reply.

I'm not sure I understand your comments. I have not noticed oil blowing back out the air intake.

What I have is a sudden release of air pressure into the crankcase. this has enough pressure to blow the stopper off the oil filler hole and spray oil all over the place. This happens suddenly and violently.

There is a check valve between the compressor, the tank and the regulator which I opened and cleaned. It seems to be working properly so I don't think the back pressure into the crankcase is coming back from the tank. It seems to be internal to the compressor itself.

I hope I am making sense with my description. Any additional thought?

BTW, great site glad I found you.

Thanks, Jim

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Jim, I'm slow, but at least my wife thinks I'm cute! :-)

It seems then, to me, that the increase in pressure is finding a path into the oil sump as it reaches cut out pressure.

I don't know the innards of your compressor.

Having said that, the coincidence of this happening on compressor cut out suggests that the air pressure over the piston, which is supposed to blow out the unloader valve when the compressor stops, is somehow making it's way into the sump.

When the compressor reaches cut out pressure, is it unloading through the unloader valve? You say it happens just before it shuts off. Is it, perhaps, happening as the pressure switch trips to shut off the compressor?

If the compressor is not unloading through the unloader valve, then perhaps the unloading air is getting into the sump, somehow, and I don't know how.

If the compressor unloads normally, then it's back to the drawing board.

Keep us posted, OK?

Bill

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