Hello there!

I have a Hitachi EC28M compressor that seems to have a faulty valve (?) that leaks air.
The problem is that I can't even identify the part, it seems to me it is not even in the assembly diagram - but I have to admit I am not experienced with fixing compressors.
I was wondering if maybe you can help identify the part or at least have a general name and function of it as that would help with my search I assume. (The official customer service was no help sadly)

This is a link here to the tool part diagram: https://www.metabo-hpt.com/docs/default-source/product-parts-list/ec28m_bd.pdf?sfvrsn=5a963966_2

And here are some pictures of the part: (it's sitting under the ON/OFF switch box)

Thank you!

Hi and thanks for the tip!
I did the test and now it seems to me that BOTH valves are defect as the compressor acts the same way with and without the unloader valve disconnected. Or from what I have read it could be the capacitator too.

I realize now that in my first post I did not describe my problem accurately. The compressor starts up normally but before reaching the max pressure the Reset button pops and stops the motor. Always on the same spot. When all tubes are disconnected the motor puffs along happily for a long time.

Now what I think the problem could be:
1. the unloader valve on the switch - this one is def broken I can hear the air hiss out from it
2. the ball valve on the tank - nr. 57 in the pdf linked above
or 3. the capacitator.

My main problem is that I can not identify the unloader valve in the assembly diagram so I could order a replacement. To me, it looks like it is not shown in the diagram. (when I asked Hitachi CS they just sent me the same pdf again)
My other problem is that I do not know how to test the capacitator...
Also, i did not find a single website to order parts from for this compressor - is that even possible or am i so bad at research?

Any help would be appreciated!
Thank you.

This video shows how to test a capacitor.

mastertoolrepair.com/how-to-test-capacitor-p-19193.html

Thank you, I will give this a go!