PART SIX:PLUMBING SYSTEMS WITH NOTES ON FIRE SUPPRESSION
freshwater tank leak or come adrift will
certainly ruin your day. Losing your water
supply well offshore can be life threatening.
Of course, you don’t have to worry about
fumes or minor drips when dealing with
freshwater tanks and plumbing as you do
with fuel systems. On the other hand, small
leaks have a tendency to get larger. You really
want all your freshwater tanks about as tight
and rugged as your fuel tanks, though they
don’t have to be pressure tested over 3 psi
(20.7 kPa) or 1 foot (0.3 m) above the maxi-
mum head to the highest vent, whichever is
greater.Freshwater Supply Piping
The schematic in Figure 20-2 shows a good
standard pressure-water system’s supply-side
piping. Most of these details are required for
safe and reliable operation. Note that the
tank vents must be higher than the fills. The
sumps and drain cocks on the tank bottom
are optional but do help with cleaning.Immediately downstream of the tank(s)
should be a filter to keep silt and other par-
ticulate matter out of the rest of the plumbing.
Most boats have just a simple mesh filter, but
you can add more sophisticated filters right
on up to UV filters that come close to steriliz-
ing the water. A good mesh filter (a strainer)
is adequate for most installations.Pressurizing the
Accumulator
From the filter, the water travels to the pres-
sure pump, which drives water through the
rest of the system. Some small, simple pip-
ing arrangements have just this pump with a
switch built into the faucets. Turn on a
faucet, and you turn on the pump. The better
and more sophisticated method is to have an
accumulator after the pump. An accumula-
tor is simply a tank with an air bladder inside.
As the pump develops pressure, it squeezes
the air bladder, and a sensor switches off the
pump when the bladder pressure reaches a
given pressure, say, 20 psi (2.9 kPa). Now
Figure 20-2. with all your faucets off, the pump will shut
Freshwater supply
piping