>Whenever my bilge pumps run, they do a fine job of pumping
>out nearly all the water in the bilge, however when they
>shut off, some residual water drains back into the bilge from
>the drain hose. This little bit of water is enough to trigger
>the pump on again and this cycling continues forever. Does
>anyone have any suggestions on how to break this cyclic behavior?
>Is this normal operating procedure? It's my understanding that
>check valves in bilge outlet lines are not a good idea, so I'd
>like to avoid that route, if possible.
>One pump is float controlled and one is electronic, both are
>relatively new, but neither one seems to know when to quit.
The fact is, that they are triggered by the amount of water in
the bilge, and it isn't the pump's fault, but the plumbing.
One solution is to use a separate switch which is placed higher
in the bilge than the amount of water which drains back through
the hose fills the bilge.
Another possibility is to minimize the amount of back-flow by
running the hose up above the level of the outlet as vertically
as possible, so that the volume of water which can flow back
is minimized... ...that is, when the outflow reaches its
highest level, it will run downhill and out the discharge.
If you do this, you MUST ensure that the outflow is above the
water-line at all times, other wise you could, conceivably,
start a siphon when the pump shuts off, thus refilling the boat :-(
So instead of this:
| Pump | //
| Pump | ||
Now, instead of containing the amount of water from end-to-end,
the line will likely only contain the amount of the vertical
portion (in practice, some MAY siphon back from the down-hill
section when the pump goes off, but probably not enough to
cause a problem. Unless your bilge sump is very small. Or
the result, if the down-hill portion is just right, might be
that the existing flow keeps a siphon running in the desired
By the way, your pump will work better as a bonus, because the
sheer weight of the column of water it is lifting will be smaller
and, once it turns the corner, gravity, and perhaps some resulting
siphon action, will be helping the pump to do its job.
Also, if the discharge DOES get immersed, the loop will make it
necessary for a siphon to start, rather than a simple down-hill
flow, in order to back-fill the boat.
If you really want to be first-rate, you could install a siphon-
breaker loop (vented loop) on the outflow, but perhaps that is