Atmospheric pressure The
force exerted by the atmosphere on the earth's surface, which allows
pump to operate. At sea level, the atmospheric pressure equals
14.7 PSI. As elevation increases, atmospheric pressure decreases,
therefore pump performance also decreases.
Brake horsepower Pump
performance can be expressed in horsepower using the following
||Brake HP = GPM x Ft./Head / 3940
water handling capability (volume) of a pump expressed as gallons
per minute (GPM).
Cavitation Status in which the pump
impeller is not receiving a full supply of material. This can
be due to reduced
flow or over rotation. Excessive pump RPM can cause a vortex in
the eye of the impeller. Air bubbles attach to the metal surfaces
under extreme pressure, implode, taking tiny bits of metal away
with each implosion, pitting the impeller and volute surfaces.
cavitation can cause severe, permanent damage to the pump components,
resulting in poor performance.
Centrifugal force The action that causes
something to move away from its center of rotation.
Centrifugal pump Uses centrifugal
force to move water or other liquids. Centrifugal pumps use an impeller
and a volute to create the partial vacuum and discharge pressure
necessary to move water through the casing. The impeller and volute
form the heart of a pumptheir design determines its flow,
pressure, and solid handling characteristics. As the impeller rotates
and churns the water, it purges air from the casing, creating an
area of low pressure, or partial vacuum, at the eye (center) of
the impeller. The weight of the atmosphere on the external body
of water pushes water rapidly through the hose and pump casing toward
the eye of the impeller. Centrifugal force created by the rotating
impeller pushes water away from the eye, where pressure is lowest,
to the vane tips, where pressure is the highest. The velocity of
the rotating vanes pressurizes the water, forcing it through the
volute and discharging it from the pump.
Check valve (swing
check valve) A device used in a suction
or discharge line that allows flow in only one
direction to prevent
reverse flow, thus isolating the material being pumped.
Critical lifts Suction
lifts greater than 25'.
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Dewatering pump Designed for clear water
applications (agricultural, industrial, and residential). As
a general rule, dewatering pumps
are limited to a 10% solids concentration and a solids size of
one-fourth the diameter of the suction inlet. For applications
solids handling capability, trash pumps should be used.
Uses a positive displacement design rather than centrifugal force
to move water through the casing, delivering a specific amount of
flow per stroke, revolution, or cycle. Due to their great air handling
capabilities, diaphragm pumps are ideal for applications involving
slow seepage at the point of suction.
Duty point The
point on a performance curve that plots flow (GPM) and head (feet).
Dynamic discharge head The sum of
the static discharge head and the discharge friction loss in
the discharge line. Also referred to as Total Discharge Head.
Dynamic suction head The
sum of the static suction lift and the suction friction loss
in the suction
line. Also referred to as Total Suction Head.
Flow rate How many gallons per minute
(GPM) of pump flow are required. Flow can also be expressed
in gallons per hour (GPH) and in million gallons per day
Float Switch A
device used to start and stop a pump based on preset water levels.
Fluid type Whether the fluid being pumped
is clean or dirty, contains any solids or abrasives, or is a hazardous
Friction loss Reductions in flow due to turbulence as water
passes through hoses, pipes, valves, and fittings. This includes both suction
and discharge friction losses.
Head Gains or losses in pressure caused
by gravity and friction as water moves through a system. It can
be measured in lbs. per square inch (PSI) or feet of water. A pump
must produce 1 PSI to push a column of water vertically 2.31 feet.
Use the following formulas to convert:
pressure x 2.31 = Max. Head Rating
Max. Head Rating χ 2.31 = Max. Pressure
High head (high-pressure) pump Capable
of handling flows at significantly higher total dynamic head ratings
(TDH). They utilize a closed design impeller and a compact volute
called a diffuser to generate the high discharge pressure needed
and cannot handle large solids.
Hose length (or pipe) The suction and
discharge hose or pipe lengths required for a given application.
Longer hoses increase friction loss, thereby reducing pump performance.
Therefore, hose lengths should be kept as short as possible.
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Impeller A rotating
disk with a set of vanes coupled to the engine or drive shaft that
produces centrifugal force within the
pump casing of a centrifugal pump.
Maximum suction lift The
height (approx. 25') that water can be lifted by a centrifugal pump
in actual conditions,
taking into consideration altitude, friction loss, temperature,
suspended particles, and the inability to create a perfect vacuum.
The 25' suction lift is attainable for cold water (60°F) at
sea level. Suction lift diminishes as elevation increases, due
to the reduction in atmospheric pressure. In addition, suction
lift decreases as the water temperature increases since warm water
contains more entrained air.
Mechanical seal A spring-loaded pump component
that forms a seal between the pump and the engine or motor. Pumps
designed for working in harsh environments require a more abrasive
Net Positive Suction Head (NPSH)
Positive flow of water to suction part of pump.
Performance curve A chart or graph that
illustrates pump performance by plotting the total head and flow
rate at various suction lifts. Performance curves for diesel-driven
pumps also show pump performance at various engine RPM's.
Prime The creation of a partial vacuum
inside the pump casing, which allows water to flow into the pump.
Seepage The rate at which the fluid being
pumped accumulates at the point of suction. Slow seepage allows
air into the pump suction, which causes some types of pump to lose
Self-priming The ability of a pump to purge
air from its casing and suction hose, creating a partial vacuum
and allowing water to flow freely into the pump. Most smaller portable
centrifugal pumps (2" to 4" diameter) require an initial
manual priming before operation is begun and then operate as self-priming.
Solids concentration Ratio of solids to
liquid in the overall volume of the material being pumped, which
is helpful in determining the proper pump for the application. Hydraulic
submersible pumps handle higher solids concentrations than diesel-driven
Solids size Average diameter of individual
particles in the material being pumped, which is important to know
when specifying a pump. Large solids can be filtered with strainers
or rock guards.
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Static discharge head The vertical distance
from the centerline of the pump impeller to the point of discharge.
(See definition for dynamic discharge head.)
Static suction lift The vertical distance
from the lowest suction point to the centerline of the pump impeller.
This distance should be kept to a minimum for maximum pump performance.
(See definitions for theoretical and maximum suction lift.)
Strainer A fitting at the end of a suction
hose that prevents solids larger than its solids handling capability
from entering the pump.
Submersible pump A centrifugal
pump designed to operate within the water source being pumped, thereby
eliminating the suction lift limitations common to other types.
Theoretical suction lift The maximum height
(33.9') that water can be lifted inside a tube under perfect conditions
(perfect vacuum) at sea level. At this point, the water inside exerts
a pressure equal to the weight of the atmosphere pushing down on
the oceans surface. Theoretical suction lift is calculated
by dividing the atmospheric pressure at sea level (14.7 lbs. per
square inch) by the weight of one cubic inch of water (.0361 lbs.).
This equals 407.2" or 33.9'.
Total dynamic head (TDH) The sum of the
dynamic suction head and the dynamic discharge head. Also referred
to as Total Head.
Trash pump Designed to
handle large amounts of debris, with a solid handling capability
of 25% by volume. As a rule of thumb, trash pumps can handle spherical
solids up to one-half the diameter of the suction inlet.
Viscosity The resistance to flow of a liquid
at a given temperature. Highly viscous liquids are thick and tend
to flow slower than liquids of low viscosity.
Volute The casing surrounding the impeller
in a centrifugal pump that collects the liquid discharged from the
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