potted reed variety. An example is the Ultra Bilge
Pumpswitch manufactured by Ultra Safety Systems
( www.tef-gel.com) of Mangonia Park, Florida. I’ve used
hundreds of these switches over the years, and they’ve
proven to be exceptionally reliable. Warranties for these
switches range from five years to lifetime. Among other
options and features, they offer extended “hysteresis”
(also called “differential”), the vertical distance between
the levels at which the switch activates and deactivates
the pump. An extended hysteresis can negate the need
for a check valve where long discharge lines and small
bilge wells cause frequent short cycling of the pump.
(With this arrangement, the pump will continue to run
for a period of time after the water has been pumped
clear of the bilge, removing as much of it as possible in
the process.) The only real weakness of the potted-reed-type switch is that an oil-fouled bilge might deposit
emulsified oil inside the switch cylinder, which can
prevent the cylinder from rising or falling. For those
who keep their bilges free of oil, this isn’t a concern.
Like a manual switch, a float switch must be capable
of carrying the steady-state load and the locked-rotor
load of the pump. If, for instance, the pump manufacturer calls for a 15-amp fuse, the float switch must
be rated to carry this load continuously. Float switches
should always be wired into the positive side of the
pump’s circuit. If the switch is wired into the negative
leg, the inside of the pump will remain positively
energized at all times. The smallest breakdown in
insulation or carbon arcing inside the pump housing
could cause this current to leak through the pump’s
shaft and into the bilgewater and immersed metals such
as seacocks or shaft logs, which will almost certainly
result in stray current corrosion of this hardware.
One additional comment on automatic bilge pump
switches is warranted. For many years, the most
common switch looked vaguely like a hinged paddle.
Inside the switch was a small drop of mercury. As the
paddle floated upward, the mercury, which is electrically
conductive, would roll back into a set of contacts,
activating the pump. This system worked exceptionally
well. The point of failure usually was the wire attached to
the float; after a few thousand cycles, the insulation
broke down, the conductors corroded, and the pump
stopped working (and the vessel may have experienced
stray current corrosion as a result of the exposed,
energized conductor).
Because of the environmental hazard presented by
mercury, these switches are no longer manufactured. But
thousands were sold, and many no doubt are still in use.
If you have one, beware of the mercury content. If the
switch paddle is crushed or shattered, the mercury could
Bilge Pumps, Part II
Top: Even properly installed crimp connectors are not up to the
harsh, corrosion-inducing conditions found in most bilges. These
connections are far from waterproof and, when lightly tugged,
they may separate, as the ones shown here did. Above: A
typical bilge pump and float switch installation accompanied
by a high-water alarm float switch. High-water alarms should
be installed so that the crew is alerted to any abnormal
accumulation of water, rather than emergency flooding alone.
