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This article will serve as a hub for all Hitachi air compressor not building pressure, related issues. It’s a very common problem for Hitachi air compressor will not build pressure, and so, this article will present the reasons why this occurs, along with current reader questions and answers.
Why My Hitachi Air Compressor Won’t Build Pressure
The most likely reasons why your Hitachi air compressor won’t build pressure are:
- Compressor intake valve failing
- Compressor pump pressure valve failing
- Compressor gasket failure
- Compressor piston seal failure
- The tank check valve is compromised
Hitachi Air Compressor Intake Valve Failing
If it is the intake valve that has failed, then the compressor will draw air in on one cycle, but then that air will blow right back out the intake valve. You will need to remove the intake filter and feel if the air is moving in and out of that opening while the compressor is running.
Hitachi Air Compressor Pump Pressure Valve Failing
A fault pressure valve will cause air to flow into the tank through the pressure valve on the compression stroke but then be drawn right back out of the tank as the piston cycle to try and draw more air in through the intake valve.
If either the intake valve or pressure valve fails (breaks or fails to seat properly due to debris build-up) then your compressor will run all day and never build very much pressure in the compressor tank.
Hitachi Air Compressor Gasket Failure
The flow path of the intake air inside the pump head is often only separated from the flow path of the pressurized air to the tank by a gasket. It is possible that your Hitachi compressor is working adequately, but as it is cycling, the air is flowing back and forth across a failed gasket inside the pump instead of being forced into the tank.
Hitachi Air Compressor Piston Seal Failure
If the rings are defective, the pumps will lose pressure and compression strength. This can also reduce the pump’s efficiency to optimize the production of compressed air. It’s worth checking the piston seal and rings at the same time.
Hitachi Air Compressor Tank Check Valve is Compromised
When the tank check valve becomes defective, the discharge head of the pump will receive a high pressure of air. It will affect the pump’s motor might and stop it from restarting anytime the tank is full. If your air tank has a defective check valve, there will be air leaks from the unloader. So you must run another spot to check carefully on the unloader valve.
Please visit our Why An Air Compressor Won’t Build Pressure & How To Fix A Compressor Not Building Pressure guide for detailed information on each reason, along with how to conduct the necessary checks! If you’re wondering why your air compressor won’t stop running, we also have a guide on this!
Reader Questions & Responses
Hitachi 2 HP 4 Gallon Model # EC12 Air Compressor Won’t Build Pressure
Question
I have a Hitachi 2 HP 4 Gallon Oil-Lubricated Air Compressor Model # EC12.
The motor sounds strong, but I’m getting hardly any air in my tanks. I check the oil and looked at the gasket and it seems to look ok. Air is coming out of the top of the motor. Don’t know if that is normal.
Response
Hello Joseph. No, the air isn’t supposed to come out of the top of the motor. This symptom makes me think that you have a valve failure, and what may be happening (since air follows the path of least resistance) is that the air that’s being ingested by the compressor piston is being blown right back out of the same inlet port since it’s easier for the air to flow that way, than down past a check valve into the tank.
Why won’t your compressor build air pressure? There are a lot of reasons found on the troubleshooting page of this site that may also be a cause, though I suspect it’s the reed valve that is causing your compressor problems.
Questioner
Is the reed valve the cylinder shape by the gauges that you can pull to release the air?
Response
No, that’s the PRV, Joseph. The reed valves are located inside the intake hole (usually there is an intake filter screwed into the intake port) and they control the air in and stop the air out so that the air can be forced into the tank.
If you have any questions about Hitachi air compressor not building pressure, please leave a comment below, with a photo if applicable, so that someone can help you!
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Hello Bill, I recently purchased an Hitachi 4 gallon ec99s off of Amazon. Not a refurbished unit but a unit that was a return in its original box. The company I purchased it from states that all of them have been tested and work great. I received the unit very timely and it appeared as if it was never used. I plugged it in and the motor ran well but it never built pressure. I contacted the company and they apologized and sent a replacement immediately not requiring the original in return. I plugged the second unit in and it… Read more »
When you say air is escaping the “start valve”, might that also be known as a pressure switch? Where on that valve is air escaping? Is there an unloader valve on the side of the pressure switch? Is air coming out there. If so, and though I cannot see from any of the photos I found, where the metal pipe from the top of the pump enters the air tank, is there a fitting there with another line that goes over to the pressure switch? If so, and air is escaping out of the pressure switch (start valve) it’s likely… Read more »
I pulled up a parts diagram and it is calling the valve on the head, opposite the intake and filter, a start valve. I think the pressure switch is lower by the tanks. So the air is coming out off the top from a valve that is screwed into the air fins on the head. You can’t see it without removing the shroud.
OK, that’s likely the cold start valve. It’s supposed to bleed air when the compressor stops, and briefly when the compressor starts. That it’s not shutting off automatically makes it suspect, and given that it’s the second compressor with the same problem, it may be that they got a bad batch.
You will find a number of sources for these types of valves if you Google “air compressor cold start valves”. Too bad that you have to do this at all.
Ok, thank you for the help.