On Thu, Apr 12, 2012 at 10:09:39PM -0400, SteveW wrote:
>
> As always, Ben, you come through with the correct cold logic! (LOL!!!)
It's that engineering/security mindset. Have to forcibly switch it off
for stuff like flirting with cute girls, etc. :)
> I realize it's probably totally impractical and for myself, I'd stick a
> check valve onto the line 6" downstream from the outflow outlet on the pump
> and call it a day.
>
> But coming up with a practical innovative low cost run dry pump with enough
> pressure to 'clear' the line to the thru-hull would be an interesting
> intillectual exercise for a "garage tinkerer".
>
> I'm one of those always looking for a completely dry (and sparkling clean -
> I'm talking eat off it clean) bilge. Haven’t found the boat that could meet
> that criteria yet. And I'm not going to spend the $$ to find a boat "built
> around" that kind of a bilge!
Well, you could borrow part of Norm's excellent idea: use something like
his milk-jug float to get the switch/whatever electronics you wanted to
use well away from the water and the pump. The after-run circuit would
be fairly simple: when the float switch closes, it not only powers the
pump but also charges a capacitor through a resistor. When the switch
opens, the voltage in the capacitor turns on a transistor (a MOSFET, I
suppose) that sits across the switch contacts. Eventually - the delay
depends on the resistor and the capacitor that were used - the cap
discharges and unlatches the transistor. Let me know if you'd like me to
send you a schematic.
From the mechanical end of it, though, you'd still need to figure out
how you're going to get to zero water in the bilge. Strum boxes won't do
it; neither will a hose cut at an angle. You'll still need that "pocket"
- but be aware that gruck will collect there and eventually plug up
whatever pickup you're using.
I think you might have to go with the Pareto Principle on this one. :)
Ben
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