I bought a Yong Heng compressor new from Yong Heng to ensure it wasn't a fake. It arrived new with the air/oil separator parts never assembled and simply tossed in the housing bottom, so the air/oil separator wasn't going to do anything but look pretty. Cutting corners is probably due to an employee wanting to make a better rate (they're paid based on how many units they assemble per day), and this is a way to save time and therefore make more money.
Pictured above are the parts sitting at the bottom of the low-pressure air/oil separator. As delivered, the compressed air will pass from the inlet port directly to the outlet port, and the excess moisture will shorten the life of the high-pressure piston rings.
The two bottom parts were fished out of the bottom of the housing. Hopefully your separator is assembled, this one wasn't.
Clean the parts, removing any debris and oil then apply medium-strength (blue) thread-lock before assembling. Thread the filter into the housing cap (shown sitting on the pick which was used to help fish out the parts, with the filter half screwed in--only two drops of thread-lock are needed, the whole thing should not turn into a blue mess when assembled).
Use another two drops of thread-lock on the fine threads of the cap and screw the air deflector on. Do not put thread lock on the threads of the cap, the black o-ring will keep it from vibrating loose so thread-lock is not needed and could damage the o-ring.
The new check valves are brass, but they can plug up. If you remove the stainless tubes to access the check valve(s) be ready to chase threads (re-tap the threads) as the assembly quality isn't always spectacular. In the case of this compressor the threads weren't tapped cleanly, and screwing the stainless fittings into the aluminum ports caused the stainless threads to cut their own path and push the chips into the compressor. Chasing the threads and cleaning the chips out solved this problem.
The high-pressure check-valve is now brass instead of steel. The spring appears to be stainless.
The valve shipped clean and nothing on it degraded. Other steel parts found elsewhere had rusted, so if these were going to corrode some evidence would be visible at this point.
