Locating Compressor leak down?

[slackdaddy1]

I completed moving my IR T30 vert 60 gal 5HP compressor to the shed.
I plumbed in an after cooler between the cylinder out put and the tank (Check valve)

I capped off the output bung and fired it up and let it build to 80 psi, then cut it off.
In 24 hours it has leaked down to 45 psi.

There is nothing hooked up to the compressor, the output bung (on the right side) is plugged with a MNPT plug and sealant.
There is a bottom drain with ball valve.
On the left are 2 bungs:
One with a tee- the pressure switch and a safety relief valve.
2nd has the checkvalve with the compressor in (including the relief/bleed off line from the switch.

I used soapy water leak detector and found nothing on any of the tank fittings and connections,,

The only things that could not be checked was the diaphragm in the switch,, or the check valve could be leaking back to the cylinder?
(this is probably a 20-25 year old compressor with original stuff.

Thoughts on finding this phantom leak ??

 

[rsanter]

Reed valves can leak

 

[slackdaddy1]

Reed valves can leak

Once the compressor is "Off",, the tank air should not be in connection with the cylinders.
And the cylinders and piping to the tank (checkvalve) are bled off by the switch.

 

[rsanter]

Once the compressor is "Off",, the tank air should not be in connection with the cylinders.
And the cylinders and piping to the tank (checkvalve) are bled off by the switch.

Check valves can leak

 

[Beerhippie]

Check valves can leak

IME, it's the odd one that doesn't, at least a little.

 

[slackdaddy1]

Check valves can leak

Yeah, thinking I should just replace that as it is original.
I may let it pump up to 100 psi, turn it off, undo the copper line from the pump to check calve, then put a balloon over the treads?

 

[The Cobbler]

then put a balloon over the treads

or soap test it.

 

[starlight_tools]

I did a soap test on a compressor the other day and still could not find the leak. I ended up having to increase the soap content in the water and tip the compressor over a bit and finally found where it was leaking out of the bottom of pipe plug that I had not touched. Very slow leak, but there it was. Also watch closely what the condition of your tank is. Old tanks rust out and become perforated, at that point stop using the compressor until you can replace the tank.

 

[Mick56]

If you have a stethoscope, maybe you could hear it

 

[RTM]

That's a little much drop for the cooling of the air.

 

[slackdaddy1]

I replaced the Check valve and that appears to have stopped the leak