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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.

Table of Contents

Why My Hitachi Air Compressor Won’t Build Pressure

The most likely reasons why your Bostitch 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 Air Compressor Won’t Build Pressure – Hitachi Air Compressor Troubleshooting Problems

Question

I have a Hitachi 2 HP 4 Gallon Oil-Lubricated Air Compressor Model # EC12.

Hitachi EC 12 air compressor
Hitachi EC 12 air compressor Photo: plumbersstock.com

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!