A piston pump uses the up and
down or back and forth movement of
a piston to displace water in a
cylinder.
As a piston is driven in
one direction, water fills the
chamber behind it. The water is
forced into the system when the
piston reverses directions. Flow
of water into and out of the chamber
is controlled by valves.
Shallow Piston pumps
can be used up to 22 feet. Pump
capacity depends on cylinder size
and strokes per minute. The
pressures it can produce are limited by the strength of the pumping equipment and motor horsepower.
Advantages of this type of
pump are that it can pump small
amounts of sand. It can also
be installed over small diameter wells. It has a constant
rate of yield (positive displacement), and is adaptable to
hand operation.
Disadvantages are that it
causes a pulsating discharge, and
may cause noise and vibrations.
This is the same as for shallow
except the pump cylinder is attached
to the bottom of the drop pipe.
As the piston moves up and down,
it pumps water up through the drop.
pipe.
Deep-well piston pumps can
lift water from 600 feet. Double
acting piston pumps can pump
65% more water with only 15%
more horsepower.
Advantages and disadvantages
for this type are the same as for
shallow piston pumps.
The basic components of
ejectors are an are a
nozzle and venturi tube
Ejectors operate as follows.
Water is delivered, under pressure by the centrifugal pump
through the nozzle of the ejector.
The sudden increase in water
velocity as the water flows
through the narrowing nozzle
decreases the pressure of the
water. As a result, the water
speed near the outside of the mouth
of the nozzle is very high, and the
pressure is very low. The low
pressure zone acts as a partial
vacuum and water from the well
is sucked from the well around
the intake pipe of the nozzle
and into a venturi tube.
The gradual enlargement of the
venturi tube decreases the water
velocity and increases the pressure.
The centrifugal pump then picks up
the flow, sending part of the water
through the discharge pipe and the
rest back to the injector.
If the well is shallow, the
pump is on the ground surface and
the jet and centrifugal pump are
adjacent to each other. Water can
be lifted from up to 22 feet deep.
For deep wells, the centrifugal
pump is still on the surface, but
the jet and venturi are submerged inside the well casing. Water can be
lifted in this way from up to 85 feet.
- Advantages-
The only moving part in the pump
is the impeller, so repairs are few.
Also, for both deep and shallow wells
jets can be offset from the well for
easy access.
-Disadvantages-
These pumps are easily damaged
by sand, and as the distance the water
needs to be lifted increases, the amount
of water diverted from the distribution
system to be injected into the jet increases. For instance, to lift water
50 feet deep, half of the water pumped
is returned to the jet. For 100 feet
of lift, 76% is diverted.
The operating principle
of the centrifugal pump can be
illustrated by considering the
effect of swinging a bucket of
water around in a circle of
water at the end of a rope. The
force pushing the water against
the bottom of the bucket is
centrifugal force. If a hole were
cut in the bottom of the bucket,
water would flow through the hole.
Further, if an intake pipe where
connected to an air tight cover
over the top of the bucket, the
flow of water out the hole would
result in the development of a
partial vacuum inside the bucket.
This vacuum would bring water
into the bucket from a source at the
other end of the intake. In this
way, continuous flow from the source
and out through the bucket would be
established.
In terms of real centrifugal
pumps, bucket and lid correspond
the pump casing, the hole and
intake pipe correspond to the intake
and discharge of the pump, and the
rope and arm perform the functions
of the impeller.
Centrifugal pumps can be used
for depths up to about 15 feet.
They are considered very efficient
for capacities of over 50 gpm and
pressures of less than 65 pounds
per square inch. They are con-
sidered ideal for use as a booster
pump to send water from a well
pump to storage or to a distribution
system.
-Advantages-
Produces a smooth and even flow.
Some types pump some sand. Centrifugal pumps are also usually reliable
with a good service life (1).
-Disadvantages-
Centrifugal pumps lose their
prime easily, and their efficiency depends upon on operating
under design heads and speed (1)
There are two basic types
of impellers. volute and
turbine. Turbine impellers
are surrounded by diffuser vanes
which provide gradually enlarging
passages in which the velocity
of the water is slowly reduced thus
transforming the velocity head into
pressure head. Volute impellers
are characterized by having no
diffusion vanes. Instead, its
impeller is housed in a case which
is spiral shaped and in which the
velocity of the water is reduced upon
leaving the impeller, with resultant
increase in pressure.
Choice between these two types
varies with the conditions of use.
The volute type is generally preferred
for large capacity, low head use - meaning shallow wells. The turbine type is
used in water wells for deep lift
installations.
Turbine Multistage pumps
operate under the same principle
as the turbine-impeller centrifugal
pump except there are one or more
impellers mounted close together on a
vertical shaft. The bowls are
positioned below the water level,
and the discharge pipe and shaft
extend to a motor on the surface.
These pump are usually used for
high capacity from deep wells - up to
1500 feet deep. The capacity and
pressure depends on design, diameter,
and number of impellers.
-Advantages-
Produces smooth, even flow and
is easy to frost proof. The long
drive shaft requires a straight and
vertical well casing.
-Disadvantages-
To repair the pump, it must be
pulled from the well.
This type operates like a
centrifugal pump except that several
impellers are mounted together on a
vertical shaft. The impellers and
motor are in a housing which is
positioned below the water level.
Submersible pumps can lift
from up to 1000 feet deep. The
pump capacity and pressure depends
on diameter, speed, and number of
impellers.
-Advantages-
Submersible pumps produce a
smooth and even flow and are easy
to frost proof. They also have a
short pump shaft to the motor.
-Disadvantages-
This pump type is easily damaged by sand in the water, and repair requires pulling the pump out
of the well.
The helical rotor pump
operates like an auger to force
water up through the pump. The
motor and auger are in a housing
under the water level.
The capacity of the pump depends
on the design of the rotor. Water
can be pumped from depths of up to
1000 feet and well casings can be
4 inches or larger in diameter.
-Advantages-
Helical rotors produce a
smooth and even flow, and they
are easy to frost proof. In
addition, there is a short pump
shaft to the motor. Sand also
damages these pumps less than any
other type.
-Disadvantages-
Repair of the pump requires
pulling it from the well.