On Tue, 14 Jun 2011 08:08:59 -0400, BQ340 wrote:

On 6/14/2011 7:37 AM, wrote:
My Sears 5 hp ( ok: 2 hp) belt drive compressor has been leaking at
the unloader valve whenever the unit is shut of or it turns itself off
(for longer than I care to admit). I have been limping along with
this problem by manually regulating the pressure via the breaker or
using enought air to keep the unit running for extended periods. I
finaly replaced the unloader valve last night. New one leaks just as
much - after a moment of thought - duh, that is what the unloader
valve is supposed to do. Problem is that the unloader valve is
unloading the tank along with any residual pressure in the pump.
Question is: where is the air leak coming from? The reed valves in
the head (I presume there are reed valves, have not opened up a
compressor in 30 years) or a check valve between the pump and the
tank? Any been there fixed that? Thought I would ask before digging
deeper into the compressor. THanks

Mine of the same vintage has a check valve in the tank where the pipe
from the compressor attaches, looks like a pipe fitting but is the check
valve. When it went I cut the pipe & installed a compression fitting
type inline.


Same experience here on a 50 year old IR T-30, including the same
symptoms the OP describes. Grainger has replacement checks, though in
my case the OEM check was much easier to install, and worth the extra
cost in avoided time and aggravation.

BTW, any old check valve is not going to be a suitable replacement.

--
Ned Simmons