Yet another Yong Heng Mod

I wonder how much difference an interstage cooler would make. Anyone know what the pressure is between first and second stage is? I have been considering wrapping the transfer tubing in copper wire to see what the effect would be. It appears to me that a moisture/oil trap between stages would be beneficial to the life of the second stage valves based on the inspection of mine.
The pressure output from the first stage is 165 -180 PSIG. When I as running Yong Hengs, I used one of the old fashioned, hand-held compression testers to measure first stage pressure when doing diagnosis. It is one of the few features I miss in other compressors.
So, ive had my yong heng for about a year. It has begun NOT pressurizing above 160-180 bar. Oil chnaged a week or so ago (second since new). Changed all the air filters in line. Still hangs up.?? Any ideas?

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So, ive had my yong heng for about a year. It has begun NOT pressurizing above 160-180 bar. Oil chnaged a week or so ago (second since new). Changed all the air filters in line. Still hangs up.?? Any ideas?
The most common problems I experienced were check valves getting gummed up and high-pressure piston failure. Some Yong Hengs and clones seem to go on and on, while others are nothing but failure after failure. I've had (5) of them but switched to GX CS3 with a Nuoge (GX CS1 clone as a spare).

If you need photos of the internals of Yong Hengs, I have many.