Absolute Pressure - See Pressure
Air or any other gas trapped in a high spot in a pipe or conduit. Since gasses are lighter than liquids, they always rise to the top of any body of liquid. These gasses will remain at that high spot until they either dissolve into the liquid or are swept down and forward in the flow by the velocity of the liquid moving through the pipe or conduit.
Air locks are a particularly difficult problem on pump intake lines because good intake design normally attempts to maintain low velocities. Without higher velocities to force the gas forward with the flow, the liquid is then forced to travel underneath the pocket of gas, causing unnecessary pressure loss and difficult priming of the pump.
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A unit of measure for electrical current. 1 ampere = 1 coulomb of charged particles moving in a conductor per second. For common use in the electrical industry those charged particles are electrons, and therefore one ampere or amp equals 1 coulomb (6.24 x 1018 electrons), moving in a conductor per second.
The more electrons moving in a conductor per second, the more powerful the magnetic field surrounding that conductor. Inductive sensors surround the wire to detect and measure the strength of the magnetic field, thereby revealing how many amperes are moving in the circuit.
Volt-Amp (VA)
When amperes are multiplied by voltage the value is called Volt-Amp (VA). VA is used to express the capability of small transformers. A 50 VA transformer supplying 24 volts to a load can deliver 2.08 amps of current to the load (50 ÷ 24 = 2.0833).
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Local air pressure or range of air pressures, at the pump or system location. ATM can be determined by various means.
A system designer can roughly estimate ATM based on the elevation of a site above Sea Level. If greater accuracy is required then it is advisable to obtain the range of ATM values from actual site measurements with a barometer or from reliable sources.
Variations of ATM due to weather (Lows, Highs, winds, and Temperature), geographical variations, and latitude and longitude, are often not significant in NPSH calculations.
When highly accurate determination of ATM is not necessary the following values apply for ATM at sea level:
U.S.
1 ATM = 14.695 psi (Usually rounded to 14.7 psi)
1 ATM = 33.957 Feet of Head
1 ATM = 29.921 Inches Mercury (Hg)
1 ATM = 406.807 Inches Water
Metric or CGS
1 ATM = 1.0132502 Bar
1 ATM = 1013.25024 Millibars
1 ATM = 760 mm Hg (Mercury) (Also stated as 760 Torr)
1 ATM = 101.32504 Kilopascals (kPa)
Rotodynamic Machine continuously imparting velocity energy into a fluid by means of a spinning impeller / propeller. The term "Axial Flow" refers to the fluid flow path which is parallel with the axle or shaft spinning the propeller. Axial Flow pumps are not centrifugal pumps because very little centrifugal force is involved in the energy transfer from the propeller into the fluid and behavior characteristics are much different than centrifugal pumps.
Axial Flow Pumps are low head high volume pumps compared to centrifugal pumps. The power curve for Axial Flow Pumps is inversely proportional to the flow rate (higher flow = less power required). The operating range for Axial Flow Pumps is small compared to Centrifugal Pumps, especially at flow rates much below BEP as centrifugal pumps can.
Specific Speed range for Axial Flow Pumps is approximately Ns>10000.
Axial Flow pumps are often used for flood irrigation, moving fluids across an elevation difference, flood control, water falls, and any other application requiring the movement of fluids with low head requirements.
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Glossary - Francis Vane (Impeller)
Glossary - Radial Vane (Impeller)
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