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Plumbing & Ventilation
Pressurized Freshwater Systems
Do you want on-demand water supply?
On-demand pumps have a pressure switch that
makes the pump build up pressure in the freshwater
line. Whenever water is demanded and the faucet
is opened, a stream of pressurized water is avail-
able. The pump turns on to maintain this pressure as
needed. By contrast, manual pumps have no pres-
sure switch, and must be turned on manually (via an
electric switch) prior to when the water is required.
Do you want an electric or a manual pump?
Some pumps use electricity to operate, and others use
muscle power. But almost any pressure water system
should have a freshwater and/or saltwater manual
pump and spigot as backup. Electrical pump failure
should not eliminate your access to fresh water.
How many outlets does the pump need
Freshwater pumps are frequently described by how
many outlets they can supply ("for 2-3 faucets"). Ad-
ditional taps or fixtures in the system might cause a
reduction in flow capacity, erratic flow, or excessive
pump cycling if several were "open" at one time.
How much capacity do you want?
Pumps will generally be selected by how many gallons
per minute (gpm) they can pump, and/or by how much
pressure they can develop. The freshwater pumps we
offer have capacities between 1.1 and 11 gpm. Some
general guidelines for sizing the pump:
Number of Fixtures Recommended gpm
Up to 3.0 gpm
Up to 4.0 gpm
More than 4.0 gpm
Do you want to pump
both fresh- and
Many galley pumps cannot be
used with saltwater because salt
will damage the valves and seals
or corrode internal metals. How-
ever, to conserve fresh water,
especially on small vessels with
limited tankage, you might want
to use saltwater for dishwashing.
A popular method uses a bucket
for the first wash cycle before
rinsing the clean dishes with
fresh water, either in the galley sink or with the deck
shower system. If you want to pump both fresh- and
saltwater, select a saltwater-capable pump like the
Paragon Jr. by Groco.
Where will you mount the pump?
determines whether you need a self- or non-self-
priming pump. Non-self-priming pumps have to be
mounted at or below the water level, so water is al-
ready in the pump chamber. They can push water
uphill against gravity. Self-priming pumps can be lo-
cated above the water level because they can draw
the water up to them when they are turned on.
What to look for
Does your boat have 12V or 24V?
We offer several
pumps for both. Amperage draw varies by capac-
ity. NOTE: Starting amperage draw might be signifi-
cantly higher than operating draw.
Which port size do you need?
pumps will have port sizes of 3/4" or 1" to allow more
flow. Some shower pumps offer multiple port sizes
between 3/4" and 1 1/2". Otherwise 1/2" NPT ports
are common on freshwater pumps.
The importance of multiple pump chambers:
More chambers generally mean smoother operation,
with less pulsation, in diaphragm pumps.
Variable speed pumps offer a notice-
able improvement over accumulator tank systems. They
change the speed of the motor to deliver the precise
amount of water wherever it is needed. There's virtually
no lag time, and there's no drastic difference in pres-
sure if two or more faucets are open simultaneously.
The pump's output under ideal (open
flow) conditions. This doesn't take into account head
height, friction in the system and other factors that
reduce output. For most boats, high gpm pumps
may not be an advantage, especially if the fixtures
only permit a limited amount of water to flow.
Run dry capability:
Some electric pumps can be
damaged by running dry. The mechanism burns up or
wears out when there is no fluid present. To prevent
this, some pumps have "run dry" sensors that detect a
lack of flow and shut off the pump to protect it.
A check valve
is a mechanical valve that only per-
mits flow in one direction. It will also prevent city
water pressure (which is higher than the pump can
handle) from going into the pump. Most diaphragm
pumps have check valves built in.
A pressure switch
opens the electrical circuit to a
pump (and turns it off) when the water in the sys-
tem reaches a preset pressure, usually 35-60psi.
It closes the circuit (and turns the pump back on)
when the pressure falls below that point. It makes
on-demand pumps function automatically.
The rest of the system
The best tanks are made of thick-
walled, high-density polyethylene, but flexible tanks
can work in an odd-shaped or inaccessible space.
Tank size depends on the space available and your
needs (anywhere from one to ten gallons per person
per day). Make sure your tank's deck fill has a tight
seal and that your tank's vent terminates inside the
boat so your drinking water supply won't be fouled
by outside water.
Most pumps and fixtures are designed for
1/2" ID hose. Be sure the hose you choose can
handle 35-40psi and is made from FDA-approved
(nontoxic) materials. Hot-water hoses must be rein-
forced to withstand high temperatures.
A sealed air chamber com-
bined with a water reservoir provides expansion vol-
ume to reduce pump cycling from minor pressure
changes and give a steady flow. Larger tanks store
enough water to eliminate pump cycles when mod-
est amounts of water are needed. Until a few years
ago, this was the last word for functional pressure
water systems. Now, variable-speed pumps have
eliminated the need for accumulator tanks.
Municipal Water Inlet:
By connecting a drinking-
water-safe garden hose between a municipal water
inlet and a faucet on shore, you'll have a continu-
ous source of pressurized water at the dock without
ever having to fill the tank or operate the pump. To
protect and isolate your pump and accumulator tank
from potentially damaging high pressure, install a
one-way check valve as shown in the diagram.
The water heaters we carry can be
operated at the dock by AC power or underway by
drawing heat from your engine's cooling water. Even
a small, 6-gallon heater is enough to provide hot
water for washing dishes or taking a short shower.
Showers, whether in the head or
out on the swimstep, greatly enhance your quality
of life onboard. High capacity pumps with large
accumulator tanks will provide the most home-like
shower. When adding an interior shower, it is neces-
sary to have a shower sump so you don't fill up your
dry bilge with slimy water every time you bathe.
On-demand water supply?
How much capacity?
Both fresh- and saltwater?
What to look for
Pressurized water systems make life aboard more
comfortable by providing water "on tap" for dish-
washing, showers and other applications. The
complexity of installing and maintaining one will
depend on the number of outlets and accessories
Where they are used:
On all boats larger than
runabouts and daysailers, fresh water on board
is both a convenience and a necessity. The fresh-
water pump is at the heart of the delivery system
that ensures a constant supply to the fixtures in
galley, head and shower.
Municipal Water Inlet
Deck Fill Freshwater Tank
How many outlets?
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