Wells & Pumps
Well types
In many areas of the country, finding potable water is as easy as getting out
a shovel and digging a hole in the ground. Okay, maybe "easy" isn't the right
word, but wherever the water table is only several feet below the surface of the
ground, part of the battle may already be over. In such a shallow-well
situation, lifting the water up to the house is going to be a little easier, if
only because the distance you have to move it is modest.
If your area doesn't have a high water table, or if it lacks a stable supply
of potable water near the surface, you must dig deeper to achieve the same
result. And because a deep well means that the water has to be lifted farther,
the strategies for moving it change.
Shallow-well pumps
These days, the most common pump for a shallow well is a jet pump. Jet pumps
are mounted above the well, either in the home or in a well house, and draw the
water up from the well through suction (see Single-Drop Jet-Pump System diagram
on next page). Because suction is involved, atmospheric pressure is what's
really doing the work. Think of the system as a long straw. As you suck on the
straw, you create a vacuum in the straw above the water. Once the vacuum is
there, the weight of the air, or atmospheric pressure, pushes the water up the
straw. Consequently, the height that you can lift the water with a shallow-well
jet pump relates to the weight of the air. While air pressure varies with
elevation, it's common to limit the depth of a jet-pump-operated shallow well to
about 25 ft.
Jet pumps create suction in a rather novel way. The pump is powered by an
electric motor that drives an impeller, or centrifugal pump. The impeller moves
water, called drive water, from the well through a narrow orifice, or jet,
mounted in the housing in front of the impeller. This constriction at the jet
causes the speed of the moving water to increase, much like the nozzle on a
garden hose. As the water leaves the jet, a partial vacuum is created that sucks
additional water from the well. Directly behind the jet is a Venturi tube that
increases in diameter. Its function is to slow down the water and increase the
pressure. The pumped water–new water that's drawn from the well by the suction
at the jet–then combines with the drive water to discharge into the plumbing
system at high pressure.
Because shallow-well jet pumps use water to draw water, they generally need
to be primed–filled with water–before they'll work. To keep water in the pump
and plumbing system from flowing back down into the well, a 1-way check valve is
installed in the feed line to the pump.
Shallow-well pumps
These days, the most common pump for a shallow well is a jet pump. Jet pumps
are mounted above the well, either in the home or in a well house, and draw the
water up from the well through suction (see Single-Drop Jet-Pump System diagram
on next page). Because suction is involved, atmospheric pressure is what's
really doing the work. Think of the system as a long straw. As you suck on the
straw, you create a vacuum in the straw above the water. Once the vacuum is
there, the weight of the air, or atmospheric pressure, pushes the water up the
straw. Consequently, the height that you can lift the water with a shallow-well
jet pump relates to the weight of the air. While air pressure varies with
elevation, it's common to limit the depth of a jet-pump-operated shallow well to
about 25 ft.
Jet pumps create suction in a rather novel way. The pump is powered by an
electric motor that drives an impeller, or centrifugal pump. The impeller moves
water, called drive water, from the well through a narrow orifice, or jet,
mounted in the housing in front of the impeller. This constriction at the jet
causes the speed of the moving water to increase, much like the nozzle on a
garden hose. As the water leaves the jet, a partial vacuum is created that sucks
additional water from the well. Directly behind the jet is a Venturi tube that
increases in diameter. Its function is to slow down the water and increase the
pressure. The pumped water–new water that's drawn from the well by the suction
at the jet–then combines with the drive water to discharge into the plumbing
system at high pressure.
Because shallow-well jet pumps use water to draw water, they generally need
to be primed–filled with water–before they'll work. To keep water in the pump
and plumbing system from flowing back down into the well, a 1-way check valve is
installed in the feed line to the pump.
Breaking the depth barrier
Unfortunately, you may have to go a little deeper than 25 ft. for your water.
Surprisingly, you can still do it with a jet pump. It simply involves separating
the jet from the motor and impeller housing and placing the jet assembly down in
the water (see Double-Drop Jet-Pump System diagram). In a typical deep-well
jet-pump configuration, one pipe mounted to the impeller housing drives water
down into the jet body that's located about 10 to 20 ft. below the minimum well
water level. A second pipe connects the output side of the jet body back to the
pump.
At the jet, the increase in water velocity creates the partial vacuum that
draws standing well water into the second pipe and then back into the pump and
plumbing system. Deep-well jet pumps use both the suction at the jet to bring
water into the system and pressure applied by the impeller to lift the water.
To prevent overpumping the well, a deep-well jet-pump installation may
include a 35-ft.-long tailpipe. It's connected to the intake end of the jet
housing and extends down into the well. If the water level dips below the level
of the jet housing, the pump operates in the same manner that a shallow-well
pump does. While flow rate drops off, water will be available until the level
drops below about 25 ft. from the jet housing-the limit for a shallow pump. The
35-ft.-long tailpipe effectively ensures that the well will never be pumped out.
Of course, the height of the jet over the water level affects performance. The
farther away it is, the less efficient the pumping becomes.
Like shallow-well systems, a jet pump in a deep-well system needs to be
primed to operate. A foot valve at the bottom of the well piping prevents water
from draining from the pipes and pump. Jet pumps that have two or more impellers
are called multistage pumps.
Moving to the source
While a jet pump can reliably handle a well several hundred feet deep, a more
effective solution is to move the pump down into the well so, instead of lifting
the water, it's pushing it up. A typical submersible pump is characterized by a
long cylindrical shape that fits inside the well casing. The bottom half is made
up of a sealed pump motor that is connected to the aboveground power source and
controlled by wires. The actual pump half of the unit is comprised of a stacked
series of impellers-each separated by a diffuser-that drives the water up the
pipe to the plumbing system.
In modern installations, the well casing outside the home is connected to the
plumbing system by a pipe that runs beneath the ground to the basement (see
Submersible Pump System diagram). This horizontal pipe joins the well pipe at a
connector called a pitless adapter. The function of the adapter is to permit
access to the pump and well piping through the top of the well casing, while
routing water from the pump into the plumbing system.
While submersible pumps are more efficient than jet pumps in delivering more
water for the same size motor, pump or motor problems will necessitate pulling
the unit from the well casing-a job that's best left to a pro. However,
submersibles are known for their reliability and often perform their role 20 to
25 years without servicing. Submersible pumps may also be used in shallow wells.
However, silt, sand, algae and other contaminants can shorten the pump's
life.
Common elements
No matter what kind of system you have, the components on the output side of
all pumps are similar.
Pumps are not intended to run continuously, and they don't start each time
you open a tap or flush the toilet. In order to provide consistent water
pressure at the fixtures, the pump first moves water to a storage tank. Inside a
modern tank is an air bladder that becomes compressed as the water is pumped in.
The pressure in the tank is what moves the water through the household plumbing
system.
When the pressure reaches a preset level, which can be anywhere from 40 to 60
psi, a switch stops the pump. As water is used in the home, pressure begins to
decrease until, after a drop of about 20 psi, the switch turns on the pump and
the cycle is repeated. You'll find the pressure gauge mounted on the tank with
wires leading to the switch that controls the pump.
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