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Hitachi Air Compressor Leaks Air – Hitachi Air Compressor Problem

Published Categorized as Air Compressor Leaking Air, Hitachi No Comments on Hitachi Air Compressor Leaks Air – Hitachi Air Compressor Problem

Air leaks can be a significant source of wasted energy on Hitachi air compressors. They will cause pressure drops in the system, as well as resulting in additional costs. This article will provide why your Hitachi air compressor leaks air, and the most likely locations if you’re looking to diagnose and fix the issue!

Table of Contents

Why Is Air Leaking From My Hitachi Air Compressor?

Hitachi air compressors leak air for several different reasons. It could be that the fittings are not sealed, the hose or pipe has a crack, or a compromised component that needs replacing.

Here’s a table of the most common components that could be causing your Hitachi air compressor to leak:

Condensate TrapsCouplings
Cylinder Rod PackingDisconnects
LubricatorsPoint-of-Use Devices
Pipe JointsPressure Regulators
Shut-Off ValvesThread Sealants
Why Hitachi Air Compressor Is Leaking Table

To help you locate your Hitachi air leak, you generally have 3 methods of detection to choose from:

  1. Listening and feeling – this is the simplest method, but not always the most accurate.
  2. Applying soapy water to an area where a leak is suspected – is a reliable but time-consuming method.
  3. Using an ultrasonic leak detector – is the best method and has quickly become an industry standard.

For more information on how to find and fix leaks on your air compressor, visit our guide!

Useful Pages on Air Compressor Leaks

Reader Questions & Responses

Hitachi EC12 Air Compressor Leaks Air – Hitachi EC12 Air compressor Troubleshooting


I have a Hitachi EC12.

The existing pressure switch was an 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 https://www.ebay.com/itm/Air-Compressor-Pressure-Switch-Hitachi-882-609-PS104PPL-/400380488858?ssPageName=ADME:L:OC:US:3160) 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.


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.



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.


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.

If you have any questions regarding the Hitachi air compressor leaks air, please leave a comment below, with a photo if applicable, so that someone can help you!

By Aidan Weeks

A passionate Mechanical Engineer with endless enthusiasm for fluid power - building off the back of over 18 years of high quality contribution and discussion stimulated by Bill Wade here at About Air Compressors. With both practical and theoretical experience in pneumatics and hydraulics, I'm putting my knowledge to work - and working my grey-matter through my research, assistance and publishing work here at About Air Compressors. Feel free to reach out any time! P.S. A HUGE shout out to Doug who really offers such great value to all visitors to About Air Compressors - once again, feeling like I'm standing on the shoulders of GIANTS by getting to work alongside such a great community

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