Fluid Power Formulas

Cylinder Speed and Motor Torque

Fluid Pressure

Pounds/Square Inch

Pressure=Force (pounds) /Unit Area (Square Inches) P=F/A or psi=F/A

Cylinder Area

Square Inches

Area= p x Radius2 inches

A=pr2

Area=(p/4)x Diameter2 inches

A=pD2/4 or A=0.785D2

Cylinder Force

Pounds

Force= Pressure (psi) x Net Area (square inches)

F=psi x A or F=PA

Cylinder Speed

Feet/second

Velocity= (231 x Flow rate (gpm))/(12x60xNet Area (square inches))

V=231Q/720A or V=0.3208Q/A

Cylinder Volume Capacity

Gallons

Volume=(pxRadius2(inches)x Stroke (inches) )/231

V=pr2L/231

Volume=Net Area (square inches) x Stroke (inches)/231

V=AL/231 L=stroke length

Cylinder Flow Rate

Gallons per minute

Flow Rate=(12x60xVelocity(feet/sec) xNet Area(square inches))/231

Q=720vA/231 or Q=3.117vA

Fluid Motor Torque

Inch pounds

Torque=(Pressure(psi)xF.M.Displacement(cubic inch/rev))2p

T=psi d/2p or T=Pd/2p

Torque=(Horsepowerx63025/RPM

T=63025 HP/n

Torque=Flow Rate(gpm)xPressure(psi)x36.77/RPM

T=36.77QP/n or T=36.77psi/n

Fluid Motor Torque/100psi

Inch pounds

Torque/100psi=F.M. Displacement (cubic inches/rev)/.0628

T100psi=d/.0628

Fluid Motor Speed

Revolutions/Minute

Speed=231 x Flow rate (gpm)/F.M. Displacement (cubic inches /revolution)

n=231Q/d

Fluid Motor Power

Horsepower Output

Horsepower=Torque Output (inch pounds) x RPM/63025

HP=Tn/63025

Pump Outlet Flow

Gallons per Minute

Flow= RPM x Pump Displacement (cubic inches/revolution)/231

Q=nd/231

Pump Input Power

Horsepower required

Horsepower input=Flow Rate Output (gpm) x Pressure (psi)/1714 x Efficiency (Overall)

Hpin=QP/1714Eff or Hpin=GPM x psi/1714Eff

Flow Rate Through Pipe

Feet/Second

Velocity=0.3208 x Flow rate Through I.D. (gpm)/Internal Area (square inches)

V=0.3208/A

Compressibility of Oil

Additional Oil required to reach Pressure

Additional Volume=Pressure(psi)xVolumeof Oil Under Pressure/250,000

VA=PV/250,000

Approximately % per 1000 psi

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