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>I still don't get why mounting it any higher will change things.
The only thing that can raise the float in a pump switch is water,
and the only way I can think of that water can get back into the
bilge and raise the float again after the it's dropped enough to shut
off the pump is by running back in from the discharge line. You
didn't say what kind of bilge pump your Aqualarm switch is operating
(or I missed it) but if it's a "normal" impeller pump, it won't get
all the water out of the bilge because an impeller only moves water
when there's water to be moved. Once it starts sucking air it won't
pick up much more water but it will "hold" water up in the discharge
hose as long as it's running. As soon as the pump stops running the
water in the hose will run back into the bilge unless there is an
anti-drainback valve in the discharge line which I believe is
considered a bad practice for bilge pump discharge lines
Since a typical bilge space is not a vertical-sided container but is
more of a slope-sided "pan" it will take "x" amount of water to raise
the water level half an inch, but it will take more than "x" amount
to raise the water level another half an inch. So moving the bilge
pump switch up a bit will usually ensure that the volume of water
that will run back into the bilge from the discharge line when the
pump stops will not be enough to activate the switch again. Some of
the Aqualarm bilge pump switches run the pump an extra 15 seconds
after the float has dropped to its shutoff position. This is another
way of ensuring that the water that drains back from the discharge
line won't raise the float enough to start the pump again, assuming
that the pump is pumping water during that 15 seconds and not just
sucking air. I don't see this feature called out in the specs for
the 20090.
____________________
C. Marin Faure
GB36-403 "La Perouse"
Bellingham, Washington
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