Those of you who read my report on my grandiose bilge system know that
I ignored the advice of the capacitance switch builder who said they
couldn't cost less than a grand and work. Well, he was right. This is
a great idea but it's not ready for prime time on most boats.

I set the whole thing up in my basement in a tub about the size of my
bilge sump with the hose let uphill to simulate the run that will go
in the boat.

Other solid state, electronic float switches have a high "On" trigger
point and a lower "Off" trigger. The See Water is instant on when
water touches the probe. Even a splashed drop seems to set it off.
There is no ON time delay at all. The instant the water drops below
the probe, an 8 - 10 second time delay starts. This is to draw the
water down low enough that backflow through the hoses won't set up an
endless cycle that drains the batteries. Unfortunately, the time delay
is totally inadequate for the length of hose run that would be found
on most sailboats.

I also noticed that the switch twice did not shut off at all and this
is while brand new and clean in a test set up. Once down in the bilge
with some stuff floating around, who knows? Fortunately, West Marine
has a great return policy and took both switches back even though I
had to hack the wires short to remove them.

I've now done what I should have first thing, made some calculations
of my sump size and hose volume. I want generous pumping capacity
which means 1 1/8" hose to avoid head losses in the long runs. The
volume of hose divided by the area of my sump is greater than the ON /
OFF range of any switch I have been able to locate.

I don't want to use check valves because a little bit of fluff sucked
into one could set up the endless pumping cycle. Also, if the water
drained back from the check valve, the line would essentially be
airbound.

I need a little over two inches of ON / OFF range and there ought to
be a half inch margin over that. I'm stumped. Anybody got any ideas?

--

Roger Long