Hello, I just put this old compressor back in service with a nice new paint job and some parts. I bypassed the original up-loader since it does not work and installed a 175 psi heavy duty pressure switch with a up-loader on it. I attached the pressure line from the head to this switch and find when it shuts off at 175 the air continuously comes out of the up-loader.

I suspect this is not normal.. is it!!..

should I conclude either air is by-passing the rings or there is a leaky valve. in other words it needs rings and valves.

or am I missing something.. somehow I imagined the uploader would release the air momentarily then close again which now doesn't seem to make sense. any thoughts?? the unit is a 2 stage unit, 3 hp 230 volt... HUGE tank.

its something though.. sitting next to my 2 vintage cars its part of the gang

maybe it had at one time a tank check valve.. don't see one. Maybe its in the cylinder head. does anyone know?

figured it out.. after removing the head I realized this unit was likely rebuilt since valves and cylinder bore were like new. no way any valves were leaking. Some pipes were replaced to the tank sometime in its life, likely the check valve was installed in that network of pipes. I ordered one to fit within the 1/2" NPT piping.. it got to solve it. maybe this post will help someone so I leave it..