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

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Hitachi EC 12 Air Compressor does not keep pressure

The safety valve lets air out after pressure reaches 120 psi. After pressure drops to 80 psi, the motor tries to start but cannot.

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To repair this problem (a) the pressure switch is not working,(b) check valve or non return valve sticking(stripe down repair and refit)

Posted on Sep 29, 2009

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ollie reece
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SOURCE: when my compressor reaches 120 psi the safety

what is the working pressure bud

Posted on Sep 27, 2009

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Why does the safety valve go off before the pressure switch on a porter cable 80 gal air compressor


The maximum pressure on most small compressors is 10 bar or 1000kpa which is about 145 psi in the old language most safety valves are set to 150 psi. I suggest you get some one to reduce the pressure switch setting. Running a compressor at elevated pressures does not give you any more air. A reasonable pressure for small compressors is 120 psi

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Compressor relief valve opens 150lbs on my d55141


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Air compressor will not restart after it builds pressure and pressure drops to 80 psi


Make sure the power cord is plugged into an adequate extension cord if one must be used. Never less than 12 gauge wire.

The start/run capacitor may need to be replaced.. If there are any ball check type valves, make sure they are not worn or sticking. they would be on the output of the compressor head itself.

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Hitachi Ec 119 compressor will not build pressure beyond 25 pounds; no air is heard leaking after I power down the machine. Is it likely the check valve or pressure switch?


If your compressor keeps running and only builds to 25psi, I would suspect the reed valves, head gaskets or a leak. With the compressor running spray soapy water on all fittings, around the head area and tank components. If no leak is found, remove the air filter and feel for suction at the intake(make sure head is not too hot). If you feel good suction at first then suction is lost after reaching 25 psi, most likely reeds or gaskets (with bad reed valves, sometimes you will actually feel air blowing out of the intake). Good luck

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Motor "bogs down" at roughly 120 psi...almost stops


You suspect this unit as being a two stage because of the unusually high cut off pressure. It is a single stage and the motor really has a difficult task and is being pushed to the limits. to reach this pressure. We usually reset the pressure to lower setting ~~ say around 140. Your pump probably has a leaking intank check valve (brass fitting at tank) or leaking valve plate in pump. Simple tests : with pressure in tank unplug compressor from outlet and listens for air leak around pressure switch. As you unplug the running compressor from outlet you should hear air leaking from pressure switch for just a moment as air is let out of airline from pump to tank. If air leaks out till zero pressure then change the valve. If tank holds pressure then valve probably ok. Next test, with no air in tank and air filter removed, plug in compressor and feel intake port for strong suction. If the valve plate is bad, suction will decrease as pressure neers the 120 mark till the point of feeling that air is actually blowing out of intake. With good valve plate there will be strong suction untill unit reaches set pressure. If valve plate is bad also change the cylinder and piston ring. Good luck with your repair.

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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?


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.

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I have a compressor that will run but if it gets up to pressure the tank will bleed all the air out. I turn the compressor off around 90 psi and I can use it then I have to turn it on then off before 120...


If I understand correctly the safety valve, item #64 on the parts diagram, is opening at 120lbs and not shutting until the tank is drained. If that is the case you most likely have a bad safety valve, part #881-493 which is available from http://www.ereplacementparts.com. The non-return valve is basically a check valve that prohibits the flow of air from the tank back to the cylinder. I hope this helps!

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1 Answer

Compressor blows off, does not maintain pressure


Hi there. This is normal. The pressure is set to stop at around 120-140 PSI as a safety measure. It probably kicks in again around 80 PSI so as to remain pressurized between 80 and 140 PSI. Since most air tools operate in this range, it is ok for the compressor to maintain pressure in that range. You do not want to adjust the maximum pressure safety release valve as it could be extremely dangerous as certain components in the compressor may only be rated up to 140 PSI or slightly higher before they fail or blow apart.

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Drops compressiom from 120-60 psi after 3 new pressure switches


When the pressure switch fails the comperssor will overpressure to the point of safety release at about 150 - 160 psi. It sounds as if your compressor is not producing enough pressure to cycle off at 120 and just keeps running. This happens when air is leaking from fittings or worn cylinder / reed valves. Don't worry, with some simple tests we will find the actual problem. I am assuming that your compressor is oilfree type. If there are leaks the compressor may not reach set pressure. I use soapy water on all connections and on the head/headvalve (remove plastic covers to get to all parts that may leak) while compressor is running. Make repairs as necessary. If still low pressure, while compressor is running and has reached max obtainable pressure (in your case 60 lbs), carefully place finger over intake port hole (remove filter). If the compressor is pumping normally but leaking there will be ample suction at intake and cause the compressor to speed-up when intake is obstructed with finger. If you feel plenty of suction and no visible (soapy water) leaks, then the problem is probably the cylinder /ring is not correctly seating /scratched and air is leaking past cylinder. Make sure that the cylinder /piston ring is properly aligned and that the lip on the vinyl ring is up toward the head. On oilfree compressors you can examine the cylinder by pushing the piston all the way up, then look for scratches neer top of cylinder. If scratched, pressure is leaking past cylinder, install cylinder kit. If you do not feel suction but rather air blowing out of the intake, (do this test when tank has reached 60 psi) then the problem is the headvalve plate/reed valves are leaking. The reeds must seal perfectly on their seats and not be bent or have obstruction. Replace as necessary. If reeds or headgasket is leaking the discharge air will be very hot. Only one other thing to check and that is the intank check valve. Easy to check. Run compressor till you have about 50+ lbs in the tank then unplug compressor. Carefully loosen the inlet hose at checkvalve and listen for air leaking out of tank. (check valve is the brass valve at tank) If leaking replace checkvalve. Use caution when removing head to try and save the gaskets. If you have oil type pump, and no air leaks (soapy water test) suspect reed valves/valve plate. Good luck on your repair and email if you have other question.

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