|
Useful Formulas
Motor Application Formulas
Output
|
Horsepower =
|
Torque
(lb. ft.) x RPM
5250 |
Kilowatts =
|
Torque (N·m)
x RPM
9550 |
|
Torque (lb. ft.) =
|
Horsepower
x 5250
RPM |
Torque (N·m)
= |
Kilowatts
x 9550
RPM |
Speed - AC Machinery
| Synchronous
RPM = |
120 x
Frequency (Hz)
Number of Poles |
|
| Percent Slip
= |
Synchronous
RPM = Full-Load RPM
Synchronous RPM |
x100 |
Time for Motor to Reach
Operating Speed (in Seconds)
| Seconds = |
Wk2
(lb. ft.2) x Speed Change (RPM)
308 x Avg. Accelerating
Torque (lb. ft.) |
| Wk2
= Inertia of Rotor + |
Inertia
of Load x Load RPM2
Motor RPM2 |
| Average
Accelerating Torque = |
[(FLT +
BDT)/2] + BDT + LRT
3 |
Where:
|
BDT = Breakdown Torque
FLT = Full-Load Torque
LRT = Locked-Rotor Torque |
back to table of contents
Shaft Stress
|
Shaft Stress (psi) =
|
HP x 321.000
RPM x D3
|
|
|
Shaft Stress (kg/mm2)
=
|
KW x 4.96 x 106
RPM x D3
|
|
|
|
|
Where:
|
D = Shaft Diameter (in or
mm)
HP = Motor Output
KW = Motor Output
psi = Pounds Per Square Inch
RPM = Revolutions Per Minute |
Centrifugal Applications
|
Affinity Laws
|
Fans and Blowers |
Flow1
Flow2 |
= |
RPM1
RPM2 |
HP = |
CFM x PSF
33000 x Efficiency of Fan
|
Pres1
Pres2 |
= |
(RPM1
)2
(RPM 2) 2 |
HP = |
CFM x PIW
6343 x Efficiency of Fan
|
HP1
HP2 |
= |
(RPM1
)3
(RPM 2) 3 |
HP = |
CFM x PSI
229 x Efficiency of Fan
|
|
|
|
|
|
|
Where:
|
Pres = Pressure
RPM = Revolutions Per Minute
|
CFM = Cubic Feet Per Minute
PIW = Inches of Water Gauge
PSF = Pound Per Square Foot
PSI = Pounds Per Square Inch |
Pumps
|
HP =
|
GPM x FT x Specific
Gravity
3960 x Efficiency of Pump
|
|
Volume of Liquid in a Tank
Gallons = 5.875 x D2 x H
1 gallon (US) of water weighs 8.35
lb.
Specific gravity of water = 1.0
|
|
HP =
|
GPM x PSI x Specific
Gravity
1713 x Efficiency of Pump
|
|
|
Where:
|
FT = Head in feet*
GPM = Gallons per minute
PSI = Pounds per square inch |
|
|
| *Head in feet = 2.31 x pounds per square inch
gravity. |
|
Where:
|
D =
Tank diameter (ft)
H = Height of liquid (ft) |
back to table of contents
|
1724 Tomich Court