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Reference Tables -- Fluid Power Formulas
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Basic Fluid Power Formulas / Hydraulics / Pneumatics
Variable
Word Formula w/ Units
Simplified Formula
Fluid Pressure - P (PSI) = Force (Pounds) / Area ( Sq. In.) P  =  F / A
Fluid Flow Rate - Q GPM= Flow (Gallons) / Unit Time (Minutes) Q = V / T
Fluid Power in Horsepower - HP Horsepower = Pressure (PSIG) Flow (GPM)/ 1714 HP = PQ / 1714
Actuator Formulas
Variable
Word Formula w/ Units
Simplified Formula
Cylinder Area - A ( Sq. In.) = π Radius (inch)2 A  =  π  R2
(Sq. In.) = π Diameter (inch)2 / 4 A  = π  D2 / 4
Cylinder Force - F (Pounds) = Pressure (psi)   Area (sq. in.) F  =  P A
Cylinder Speed - v (Feet / sec.) = (231 Flow Rate (gpm)) / (12 60 Area) v   =  (0.3208 gpm) / A
Cylinder Volume Capacity - V Volume = π Radius2 Stroke (In.) / 231

V = π R2 L / 231

(L = length of stroke)

Cylinder Flow Rate - Q Volume = 12 60 Velocity (Ft./Sec.) Net Area(In.)2 / 231 Q = 3.11688 v A
Fluid Motor Torque - T Torque (in. lbs.) = Pressure (psi) disp. (in.3 / rev.) / 6.2822 T  =  P d / 6.2822

Torque = HP 63025 / RPM T = HP 63025 / n
Torque = Flow Rate (GPM) Pressure 36.77 / RPM T = 36.77 Q P / n
Fluid Motor Speed - n Speed (RPM)  =  (231 GPM) / Disp. (in.)3 n  =  (231 GPM) / d
Fluid Motor Horsepower - HP HP = Torque (in. lbs.) rpm / 63025 HP  =  T n / 63025
Pump Formulas
Variable
Word Formula w/ Units
Simplified Formula
Pump Output Flow - GPM GPM = (Speed (rpm) disp. (cu. in.)) / 231 GPM =  (n d) / 231
Pump Input Horsepower - HP HP =  GPM Pressure (psi) / 1714 Efficiency HP  =  (Q P) / 1714 E
Pump Efficiency - E Overall Efficiency = Output HP / Input HP EOverall = HPOut / HPIn X 100
Overall Efficiency = Volumetric Eff. Mechanical Eff. EOverall = EffVol. EffMech.
Pump Volumetric Efficiency - E Volumetric Efficiency = Actual Flow Rate Output (GPM) / Theoretical Flow Rate Output (GPM) 100 EffVol. = QAct. / QTheo. X 100
Pump Mechanical Efficiency - E Mechanical Efficiency = Theoretical Torque to Drive / Actual Torque to Drive 100 EffMech = TTheo. / TAct. 100
Pump Displacement - CIPR Displacement (In.3 / rev.) = Flow Rate (GPM) 231 / Pump RPM CIPR = GPM 231 / RPM
Pump Torque - T Torque = Horsepower 63025 / RPM T = 63025 HP / RPM
Torque = Pressure (PSIG) Pump Displacement (CIPR) / 2π T = P CIPR / 6.28

 

General Fluid Power Guidelines:

Horsepower for driving a pump: 

For every 1 hp of drive, the equivalent of 1 gpm @ 1500 psi can be produced.

Horsepower for idling a pump: 

To idle a pump when it is unloaded will require about 5% of it's full rated power

Wattage for heating hydraulic oil: 

Each watt will raise the temperature of 1 gallon of oil by 1 F. per hour.

Flow velocity in hydraulic lines: 

Pump suction lines 2 to 4 feet per second, pressure lines up to 500 psi - 10 to 15 ft./sec., pressure lines 500 to 3000 psi - 15 to 20 ft./sec.; all oil lines in air-over-oil systems; 4 ft./sec.

 



 

 

 

 

 


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