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Pumps
Glossary
Atmospheric pressure
— The force exerted by the atmosphere on
the earth's surface, which allows a centrifugal 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 formula:
Brake HP = GPM x Ft./Head / 3940
Capacity —
The 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 and, under extreme
pressure, implode, taking tiny bits of metal away with each implosion,
pitting the impeller and volute surfaces. Excessive 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 pump—their 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.
Centrifugal
pumps offered by Sunbelt Rentals include dewatering, trash, and
submersible types.
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'.
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 requiring greater solids
handling capability, trash pumps should be used.
Diaphragm pump
— 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. Sunbelt Rentals offers both
gas and
air-powered diaphragm pumps, including special-purpose models for
handling hazardous materials such as corrosive chemicals
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 (MGD).
1 MGD = 700 GPM.
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 material.
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:
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Max. pressure x 2.31 =
Max. Head Rating
Max. Head Rating ÷ 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. Sunbelt Rentals
offers diesel-driven high head pumps from 3" to 12" diameter and 4"
diameter electric submersible high head pumps.
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.
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 resistant seal
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 RPMs.
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 their prime.
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. All larger, diesel-driven pumps
offered by Sunbelt Rentals (4" to 12" diameter) feature a self-priming
device that separates the air and water, allowing the pump to run dry and
re-prime itself without manual priming. Submersible pumps are also self-priming
since they intake water directly from the body of water without any
suction lift.
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 trash pumps.
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.
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. Sunbelt Rentals offers
both electric and hydraulic submersible pumps.
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 ocean’s 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. Larger, diesel-driven trash pumps offered by Sunbelt (4" to
12" diameter) are designed to handle 3" diameter solids.
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 impeller.
Pump
Terms...
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Inlet/Intake
- Refers to the opening through which water enters the pump head.
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Outlet/Discharge
- The opening through which water exits the pump.
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Flooded
Suction/Gravity Fed
- Liquid source is higher than the pump, and liquid flows to pump by
gravity. Recommended for centrifugal pump installations.
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Shutoff
- Point in
which pump will not push water passed the listed feet in a vertical
column . No flow past the listed vertical feet. This does not effect the
horizontal run but if the run is very long say 50 or 100 ft. then
friction comes into play.
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Flow
- The measure of the liquid volume capacity of a pump. Given in Gallons
Per Hour (GPH) or Gallons Per Minute (GPM) , as well as Liters Per Minute
(LPM) and Milliliters Per Minute (ML/M).
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Head
- Another
measure of pressure, expressed in feet. Indicates the height of a column
of water being lifted by the pump, neglecting friction losses in piping.
If pump is submerged, the head can be measured from the surface of the
water. Head ( Ft. of Water) = 2.31 PSI. Example: 10 feet equals 4.32 PSI.
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Seal-less
- No seal is used, power is transmitted from the motor to pump impeller by
magnetic force. Example is Magnetic Drive Aquarium Pumps and Wet rotor
pumps. Example : Little Giant aquarium pumps, PES Wet Rotor Models (most
mini pumps) and Cal "P" Models.
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Submersible
- A pump which operates only when totally submersed in the fluid which is
being pumped, with water-proof electrical connections or cord , using a
motor which is cooled by liquid.
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In-Line
- A pump which operates in open air , by connecting tubing to the inlet
and discharge outlet.
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Dual Purpose
- This versatile pump category is designed to operate submersed or in-line.
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NPT
- Refers to the
National Pipe Thread standard measurement.
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MNPT
- This refers to female pipe thread, in which the threads are on the inner
side of the connection fitting.
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Thermally
Protected
- Mechanically safety device in the motor to prevent overheating.
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Impedance
Protected
- A non-mechanical method of preventing motor overheating. The motor coil
is designed to "impede" excess current, resulting in a stabilized motor
temperature.
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Barbed Fitting
- As apposed to a threaded fitting , rings projecting outward around
fitting designed to grip hose. Usually measured in O.D. (outside diameter)
, as apposed to hose measured in I.D. (inside diameter).
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Quick Disconnect
- Fittings that are locked on the the pump ports with a latch or locking
device to convert pump ports to threaded or barbed connections , usually
used on high pressure pumps.
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Relay
- Electrical solenoid with heavy contacts designed to absorb high current
or high amp draw , usually for motors with 3 HP or larger or used with
sprinkler timers to activate a sprinkler pump. Coil voltage of solenoid
may vary depending on control device, usually coil voltages come in 24V ,
110V or 230V AC , amp and horsepower ratings for contacts are usually
listed.
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Kilowatt(1000
watts) Hour
- Electrical measurement designed to bill customers based on usage per
hour. Watts are listed for every unit , power consumption and cost is
dependent on the KILOWATT HOUR charged in your area. If a pump states that
it uses 1000 watts and your power company charges you 10 cents a kilowatt
hour then it cost's you 10 cents an hour to run that unit and if the pump
list's 250 watts then it cost's you 2.5 cents per hour to run that unit.
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Centrifugal pump
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moves water by displacing liquid from the center of the impeller as it
spins to the outer part of the impeller creating a vacuum in the center by
means of centrifugal force. The diameter of the impeller predicts the
pressure and the width predicts the water flow. Impellers can spin at 3600
RPM and 1800 RPM and other speeds , all fountain pumps are centrifugal.
This type of pump is not self priming except in the case of sprinkler
pumps , pumps with leaf baskets and pumps with foot valves installed (jet
pumps).
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Positive
Displacement pump
- remove water from a cavetti or cylinder by directly applying pressure to
a diaphragm or piston or a flexible impeller and cam. Check valves are
used to preserve the pressure down line except in the case of the flexible
impeller and cam. Usually diaphragm or flexible impeller or piston pumps
are used for more exact amounts of water and for higher pressures. This
makes them ideal for solar applications , RV's, pressure washers, small
cabins, R.O., misters or situations where water demand is low but pressure
demand is high. A centrifugal pump is limited in the pressure it can
produce unless the design of the pump allows for impeller stacks. This
type of pump is usually self priming a few feet.
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terminology common to their
applications.
It was explained earlier in this online pump school
that pumps lift water with the aid of atmospheric pressure then
pressurize and discharge it from the casing. The practical suction lift,
at sea level, is 25 feet. The published specifications of most pump
manufacturers will list this as maximum suction lift.
Pump performance is measured in volume as gallons per minute
(GPM) and in pressure as head. In general a
trade off occurs between head and flow with an increase in head causing
a decrease in flow and vice versa.
head refers to gains or losses in pressure caused by
gravity and friction as water moves through the system (see
figure below). It can be measured in lbs/in2 (PSI) but is
most commonly listed in feet of water.
To illiustrate this consider that a Multiquip 3 inch trash pump is rated
with a maximum head of 90 feet. A pump must produce 1 PSI to push a
column of water vertically 2.31 feet, therefore dividing the maximum
head rating of a pump by 2.31 will provide the maximum pressure
capability of the pump.
90 (ft/head) / 2.31 (ft/head) = 38.96 PSI
Similarly multiplying 2.31 by the maximum pressure capability of the
pump will provide the maximum head rating of the pump.
2.31 (ft/head) / 38.96 PSI = 90 (ft/head)
Depending on how the measurement is taken suction lift and head may also
be referred to as static or dynamic. Static indicates the
measurement does not take into account the fritcion caused by water
moving through the hose or pipes. Dynamic indicates that losses due to
friction are factored into the performance. The following terms are
usually used when referring to lift or head.
Static Suction Lift - The vertical distance from the water line
to the centerline of the impeller.
Static Discharge Head - The vertical distance fromthe discharge
outlet to the point of discharge or liquid level when discharging into
the bottom of a water tank.
Dynamic Suction Head - The Static Suction Lift plus the
friction in the suction line. Also referred to as a Total Suction
Head.
Dynamic Discharge Head - The Static Discharge Head plus
the friction in the discharge line. Also referred to as Total
Discharge Head.
Total Dynamic Head - The Dynamic Suction Head plus the
Dynamic Discharge Head. Also referred to as Total Head.
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