So, where does your air escape from?

I am not sure. By the time I had unplugged it and dragged it out from
under the lathe, it had reset. I was able to feel that it was coming
from around the switch box. I turned it back on but it operated
normally. Hindsight being what it is, I should have dragged it out
before unplugging. sigh

I'm with you about the valve. I have just checked CH troubleshooting
guide on their site and it suggests the check valve needs replacing. I
can't find my model number there so have left a message to see what's
what. I bought this in about '98 so they may no longer support it for
parts. I'll be really ****ed off if that's the case.

vbg Sears HP I am guessing. I think I did a calc some time back and
it was about 2.5hp based on the Watts rating. Still a lot of power to
eat if it was running all night.

Where did you buy the new check valve? I might just do that if CH no
longer support this model. The unloader worked fine when I switched it
back on and but very unlikely it was the cause.

Dave