Service Factor is abbreviated as SF.
NEMA MG1 - 1.42 defines SF as a multiplier, which when multiplied by the horsepower rating for the motor, indicates a permissible horsepower loading on the motor, under the conditions stated for the service factor.
A motor with a SF of 1.0 has NO Service Factor. Therefore, the motor should not be operated at horsepower loads greater than the motor's horsepower rating (current levels greater than FLA), for more than brief periods.
A motor with a SF of 1.15 has a 15% Service Factor. The motor can operate safely at current levels 15% greater than FLA.
A motor with a SF of 1.25 has a 25% Service Factor. The motor can operate safely at current levels 25% greater than FLA.
Service Factor and the motor's FLA are concerned primarily with internal heat development in the motor caused by current levels above the motors designed capacity, especially in the windings. Motors are designed to withstand a given amount of heat development due to electrical current levels, When current rises above a certain level, motor heat exceeds the motor design capacity, deteriorating the winding insulation and other components.
Example
A 30 horsepower motor has an FLA of 79 amps:
If the motor has a Service Factor of:
SF = 1.0 - Maximum continuous current = 79 amps
(79 x 1.0 = 79)
SF = 1.15 - Maximum continuous current = 90.85 amps
(79 x 1.15 = 90.85)
SF = 1.25 - Maximum continuous current = 98.75 amps
(1.25 x 79 = 98.75)
Important Note - NEMA MG1 9.15.1 states that continuous operation of a motor at current levels above FLA, but within the Service Factor, reduces motor life expectancy.
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Article - Power Characteristic
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Sleeve Bearing - See Non-Rolling Element Bearings
Liquids containing solid particles in suspension or carried within the flow. Generally, liquid slurries contain solid particles that will settle out to the bottom or float to the top if the liquid is allowed to be at rest.
Slurries are considered Non-Newtonian fluids for many purposes, however Slurries may be considered Newtonian fluids for NPSH calculations.
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Vernacular for pressure or head developed by a pump when there is no (zero) flow while the pump is operating.
A dimensionless value used by pump experts to analyze how a pump imparts energy into a Fluid. This numerical value describes the relationship between the following factors for any specific pump: Rotative Speed (rpm), Volumetric Flow Rate (gpm), and Head (feet).
Ns is the abbreviation used for the American system of RPM, GPM, and Feet of Head.
Ns is useful for the following purposes:
Helpful in the initial selection of the most correct pump for a specific application.
Predictive of the approximate Power Characteristic for a pump during the selection process, and in diagnostics of unknown pumps.
Informative about the range or window for a pump.
Specific speed can be considered short-hand for a pump expert when actual product data is not immediately available, and for assisting in the selection of a pump from thousands of pumps that could be considered, without having to examine the data for each pump.
Actual manufacturer's test data are required to know the pump characteristics accurately.
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Glossary - Net Positive Suction Head
Glossary - Suction Specific Speed
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Article - Power Characteristic
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Standard Test Conditions (STC)
The agreed upon conditions under which pump characteristics are determined experimentally and then reported by the testing agency or manufacturer. Without the STC, the pump characteristic has little meaning. For the water pump industry, by far the most common STC would be the Hydraulic Institute (HI) standards. For Centrifugal pumps the standard is ANSI/HI 2.6. For vertical centrifugal pumps the STC is ANSI/HI 11.6.
By common usage, a device that removes larger or macroscopic debris from a fluid. Fluid enters into the system through a strainer, which by various means allows the passage of fluid while catching or preventing larger debris or particles from passing through.
Strainers usually use screen, woven wire cloth, bar grille, V shaped wire, perforated metal, and expanded metal to catch and prevent debris from entering into the system.
FILTERS - Common vernacular differentiates between "strainers" and "filters". Strainers remove larger macroscopic debris from a fluid, while filters remove smaller and often microscopic particles.
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This word describes what we observe and how we describe the flow of any fluid moving as a result of atmospheric pressure.
Fluids flow only when acted upon by gravity, pressure, or application of a pushing force. Fluids in high pressure areas move towards low pressure areas by diffusion. When we "suck" water up a straw we may describe it as pulling water up the straw, but in reality we are simply creating a low pressure area in our mouth, and then atmospheric pressure pushes the water up the straw and into our mouth.
The same applies to pumps. Pumps moving free flowing non-viscous fluids such as water, do not pull fluid from the source, but rather, the pump creates a low pressure area at the eye of the impeller, and then other pressure sources push the fluid into the pump. Some of the sources that push fluids into pump intake nozzles are:
Atmospheric Pressure (Pressure on a fluid due to the weight of earth's atmosphere)
Pressure due to Elevation or Submergence (Gravity Potential Energy)
Pressure from other pumps
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Suction Cavitation - See Glossary - Cavitation
A dimensionless value similar to Specific Speed, used by pump experts to analyze how a pump responds to various input pressures. This numerical value describes the relationship between the following factors for any specific pump: Rotative Speed (rpm), Volumetric Flow Rate (gpm), and NPSH (in feet).
Suction Specific Speed is useful for the following purposes:
Informative about required margin of NPSHA over NPSHR.
Predictive of a pumps operating range or window.
Informative about the importance of Incipient Cavitation.
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