Yong Heng leaking out low pressure side Pipe

[Thiel]

Hey guys,

my jong heng starts leaking out of the connection pipe from the low pressure side to high pressure cylinder side.
i tried to tighten it up but it still leaks.

can you help me to identify the thread ?

[truck]

If the air is leaking where you have it circled I'd be looking at the compression fitting. 

[Thiel]

yes, thats the leaking spot.

the compression fitting = pipe ?

it seems to be a press fitting

i cant remove the nut further because the bended part of the pipe is too wide

these two surface areas look good to me

if pushed together by hand i cant feel any resistence or slack

[Norm_m]

I had issues with the compression connections leaking on My YH and with the short bends on the tubing making it impossible to slide the compression nuts back you should remove the tube form the compressor and blow out the area inside the nut with air to make sure there is no tiny pieces of anything around the ferrule. I then apply a tiny bit of White Lithium lube around the ferrule on the tubing. Use two wrenches when installing the nut back on, one on the nut and one on the fitting.

[tracker1955]

Unfortunately, these are metric compression connections and may be hard to source without ordering them from China through aliexpress. If you cannot get them to seal by just tightening the two connections alone I would try about two wraps of teflon tape around the ferrel and then re-tighten the nut again. The teflon will bunch up around the ferrel and get jammed up between the nut and fitting enough to make a seal. I've done this many times before with plumbing, just haven't tried it on something with a lot of pressure though, fortunately, it's on the low side and not on the high side. Hope you get it sorted out.

[Hoosier Daddy]

Push the top blue button on your calipers that says "mm/inch". Also, metric threads are measured in how many centimeters it is for 10 threads not threads per centimeter.
That will help you find the right metric fitting. 

[dlee]

fyi- i measured the fittings on mine awhile back and labeled a couple of pics. This was before I installed the cyclone separator between the 1st and 2nd stages. But here they are for reference...

[elguapo99]

I would use a flare nut wrench to tighten those fittings so as not to distort the fitting on the tube.

[truck]

McMaster-Carr sells metric compression fittings.  https://www.mcmaster.com/#

[Thiel]

wow, thanks for your help.
i had not expected that they use metric threads lol. now it is much easier for me

my leak is sealed but i dont know how exactly i did it. i used loctite 290, waited a few hours, turned it on - leaked again. tightened a little more (i know the loctite broke) but it was sealing now!!
but the pressure still did not went up

checked all screws and connection with soapy water - nothing. uncrewed the burst disks a tiny bit - bubbles, okay this should happen with soapy water. 
i prepared myself for a last try and the needle went crazy fast up (im using a dead end plug / test plug in the filling hose) i stopped at 3700psi. i filled a few small air pistol cylinders to 3000 psi and it looks good to me for now.
dont ask for explanations