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the motion control and electrical / mechanical power
transmission fields. Let our combined experience of
over 400 years design a solution for you.
  • •







 
   
Handy Formulas


  Ohm's Law
Ohms = Volts/Amperes (R = E/I)
Amperes = Volts/Ohms (I = E/R)
Volts = Amperes x Ohms (E = IR)

Power - A/C Circuits
Efficiency =    746 x Output Horsepower
                              Input Watts
Three-Phase Kilowatts =     Volts x Amperes x Power Factor x 1.732
                                                              1000
Three-Phase Volt-Amperes =     Volts x Amperes x 1.732
3-Phase Amperes =                    746 x Horsepower                   
                                   1.732 x Volts x Efficiency x Power Factor
3-Phase Efficiency =                      746 x Horsepower               
                                     Volts x Amperes x Power Factor x 1.732
Three-Phase Power Factor =               Input Watts       
                                               Volts x Amperes x 1.732
Single-Phase Kilowatts =     Volts x Amperes x Power Factor
                                                          1000
Single-Phase Amperes =               746 x Horsepower            
                                         Volts x Efficiency x Power Factor
Single-Phase Efficiency =              746 x Horsepower            
                                          Volts x Amperes x Power Factor
Single-Phase Power Factor =         Input Watts   
                                                Volts x Amperes
Horsepower (3-phase) =     Volts x Amperes x 1.732 x Efficiency x Power Factor
                                                                         746
Horsepower (1-phase) =     Volts x Amperes x Efficiency x Power Factor
                                                                    746

 

Power - D-C Circuits
Watts =     Volts x Amperes (W = EI)
Amperes =     Watts (I = W/E)
                             Volts
Horsepower =     Volts x Amperes x Efficiency
                                         746

 

Speed - A-C Machinery
Synchronous RPM =     Hertz x 120
                                     Poles
Percent Slip =     Synchronous RPM - Full-Load RPM x 100
                                      Synchronous RPM

 

Torque - Horsepower
Torque (lb.-ft.) =     Horsepower x 5250
                                      RPM
Horsepower =     Torque (lb.-ft.) x RPM
                                     5250

 

Time for Motor to Reach Operating Speed (seconds)
Seconds =           WK2x Speed Change       
                    308 x Avg. Accelerating Torque
WK2=     Inertia of Rotor + Inertia of Load (lb.-ft.2)
Average Accelerating Torque =     [(FLT + BDT)/2] + BDT + LRT
                                                                    3
FLT = Full-Load Torque BDT =     Breakdown Torque
LRT =     Locked Rotor Torque
Load WK2 (at motor shaft) =     WK2 (Load) x Load RPM2
                                                       Motor RPM2
Shaft Stress (P.S.I.) =         HP x 321,000     
                                     RPM x Shaft Diam.3

 

Resistance - Temperature
RC =     RH x (K + TC)
               (K + TH)
RH =     RC x (K + TH)
               (K + TC)
K =     234.5 - Copper
   =     236 - Aluminum
   =     180 - Iron
   =     218 - Steel
RC =     Cold Resistance (°C)
RH =     Hot Resistance (°C)
TC =     Cold Temperature (°C)
TH =     Hot Temperature (°C)

 

Vibration
D =     .318 (V/Hz) D= Displacement (Inches peak-peak)
V =      ¶(Hz) (D) V = Velocity (Inches per second peak) ¶=pi
A =     .051 (Hz)2 (D) A = Acceleration (g's peak)
A =     .016 (Hz) (V) Hz = cycles per second

 

Volume of Liquid in a tank
Gallons =     5.875 x D2 x H
D =     Tank Diameter (ft.)
H =     Height of Liquid (ft.)

 

Centrifugal Applications
Affinity Laws for Centrifugal Applications
Flow1     =     RPM1
Flow2            RPM2
Pres1     =     (RPM1)2
Pres2            (RPM2)2
BHP1     =     (RPM1)3
BHP2            (RPM2)3

 

For Pumps
BHP =     GPM x FT x Specific Gravity
               3960 x Efficiency of Pump
BHP =     GPM x PSI x Specific Gravity
               1713 x Efficiency of Pump
Head in Feet =     2.31 PSIG

 

For Fans and Blowers
BHP =              CFM x PSF          
              33000 x Efficiency of Fan
BHP =             CFM x PSW         
              6344 x Efficiency of Fan
BHP =            CFM x PSI          
              229 x Efficiency of Fan

 

Where
BHP =     Brake Horsepower
CFM =     Cubic Feet per Minute
FT =     Feet
GPM =     Gallons per minute
PSI =     Pounds per square inch
PSIG =     Pounds per square inch gravity
PSF =     Pounds per square foot
PIW =     Inches of water gauge
Specific Gravity of Water =     1.0

 
 
 


Power Torque Incorporated   425 Old State Rd (St Louis), Mo 63021
800-878-2250 • 636-343-2250 • fax 636-343-4374 • email info@powertorque.com
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