On Monday, September 15, 2008 10:11:18 PM UTC-5, Paul Franklin wrote:
On Mon, 15 Sep 2008 08:07:11 -0700 (PDT), jpj
wrote:

This weekend, possibly beyond my scope of ability, I tried to replace
the pressure switch on my sewage pump (Hydromatic skv40). I got a new
Hydromatic pressure switch from a local plumber's parts dept - looks
just like the one I'm replacing.
I thought all I would have to do is remove the old pressure switch and
attach the new one. After getting it attached and piggy backing the
pump cord/plug, I filled the basin with water, but the pressure switch
never kicks on. I can reach in and push the bottom of the switch and
the pump kicks on, but it isn't firing by itself.

This was the same problem with the one I am replacing. The pump works
fine when I plug it directly into the wall so I assumed it was the
pressure switch? How does the pressure switch work? Does the basin
have to be air tight to create enough pressure?

-Thanks -

Since it works when you press on it, you know it's wired right. The
diaphragm switches are tripped by the difference between atmospheric
pressure on one side of a diaphragm, and the pressure of the --ummm--
"water" on the other side. Generally the water needs to be 8-12
inches above the switch before it will turn on; is it deep enough? The
basin does not need to be air tight.

Also, diaphragm switches are often vented through the cord. A thin
plastic tube runs from the dry side of the diaphragm, up through the
cord, and out through the side of the piggyback plug. You can see the
little tube sticking out the side. It's important that this vent not
be covered with tape, etc. The vent is what maintains atmospheric
pressure on the dry side of the switch. If the end of the vent is
covered, it can cause the switch to either not turn on, or not turn
off. If you have any sharp bends or kinks in the cord, they can also
cause the vent to be blocked.

HTH,

Paul F.

Hey Paul, I know this is an old post but I just wanted to say thanks because this was the answer to my problem as well. I had debris clogging the pump initially but once I cleaned it out I couldn't get the pump to turn on automatically. I wasn't letting enough water fill the tank.

Thanks again,
Dustin