Sudy Nim wrote:
Is it better to have the check valve located at the base of the pump
near the inlet or further away on the discharge pipe above the pump?
Also, would two check valves be of advantage, one at the base another
a couple of feet above the base? TIA

The check valve is located as close to the pump as is practical. I have NO
idea what the other poster is talking about w/r to not on the pump,
and -drilling- an airhole. It makes no sense, and drilling airholes is
silly as there IS no air to create a suction in a properly installed sump
pump system; it's not a closed system.
My current sump came with the valve pre-screwed into the pedestal, ready
for th PVC to connect to it. ANY instructions I've seen on the check valves
I've had to purchase ALWAYS have shown the check valve screwed into the sump
pump via the threads provided for it.

In general, the check valve should be close to the pump so that there is
less air to trap in the pipes between the pump and the valve; gives it a
faster startup and the water standing in the pipe won't compress and cause
"spurts" when the pump comes on.

I can see zero advantage to two check valves unless you're just thinking of
redundancy. However, each chack valve does offer a finite resistance to the
flow of water, so there would be some slowing of the water movement; no idea
how much. It IS a good idea to have one on hand though, just in case it's
needed. They're very easy to replace. So I don't suppose it'd hurt a LOT,
especially if the water didn't have to pump upwards very far, but ... I
really see little benefit. I seem to get about ten years out of a sump
pump, and have never yet had a check valve go bad on me.

http://en.wikipedia.org/wiki/Sump_pump
and also:
http://en.wikipedia.org/wiki/Check_valve

HTH
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