Stanley Silent Compressor Repair
I own a small, oil-less compressor sold by Stanley. It really is a product developed by Italian company FNA and licensed to different companies.
I believe the compressor is sold under at least these names:
- Airboy Silence 116 OF E
- NuAir B2BE104
It's a nice little compressor which has enough power for a nail gun and small HVLP paint jobs.
Unfortunately after about three years, it first started to leak air and then never stopped pumping even when the pressure reached the maximum of pressure, causing the safety valve to open.
I contacted the Stanley support for repairs, but they basically said that they don't provide any support or repairs for licensed products like this and I should contact the seller instead 
.
I also contacted three compressor repair companies in Berlin and only one of them responded. However the response was pretty much what I expected: a repair would cost more than the ~140 EUR for a new compressor.
So it was time to figure out how to repair it myself. I watched a bunch of YouTube videos and most of them said that symptoms like mine were caused by a broken check valve.
I found an schematic drawing online(local copy) that lists the valve as “992 9430214 KIT NOT RETURN VALVE PZ”.
Searching for 9430214 brings up two German sellers for the check valve assembly: drehen-fraesen-bohren.de and cnc-shop.mobasi.com. I ordered at the first shop and a couple of days later, I had my new valve.
Opening the compressor is relatively easy. Release the pressure and unplug the compressor first! Remove all the screws on the right side and pull off the housing. Then reach in and unplug the cables from the switch, remove the screws of the left side and pull off the other half of the housing. Next unscrew the feet of the pump, so it can be moved out of the way. Remove the cable zip ties, so you can move the cables more freely.
All fittings can be removed much easier when the sealing compound is heated using a heat gun. For re-sealing I used TEC-100 "Liquid Hemp".
I replaced the check valve assembly (keeping the original electro-magnet, assuming it was not broken and not wanting to rewire it). Once everything was assembled again… the symptoms were as before. 
At least I now actually understand how the whole check valve assembly works, which I thought is pretty interesting:
Since I was back at square one, I looked for any other possible leaks. I put soapy water on all the connections but they were all looking fine. But when I leaned in closer, I could feel air flow in my face! And that's when I tried soapy water on the sides of the pressure sensor… Bingo!
The pressure switch turns on the pump whenever the pressure of the tank is below 6 bar and turns it off when 8 bar are reached. And that switch was clearly broken.
The manual lists it as part number 9430208. It's labeled as SK-0608 230 VAC 10A Off: 8bars On: 6bars. I could not find an official replacement part for it.
But knowing that 8 and 6 bars are about 120 and 90 PSI, I was able to find similar pressure switches.
I ordered this one and a 1/4" to 1/8" adapter and replaced the old one. And this time it worked!
