# Hydraulic Formulas, Hydraulic calculations, Hydraulic considerations Hydraulic Formulas speaks to hydraulic calculations and hydraulic considerations which are taken into account when dealing with hydraulic systems.

Torque and Horsepower relations

T = HP X 5252 + RPM HP = T X RPM + 5252 RPM = HP X 5252 + T Torque values are in foot pounds

Metric

T + Kw X 9543 + RPM Kw = T X RPM = 9543 RPM = Kw X 9543 + T

T = Torque, Nm (Newton-meters) RPM = Speed revs per minute Kw = Power in Kilowatts

Hydraulic (fluid power) horsepower

HP = PSI X GPM +1714 PSI is gauge pressure in pounds per square inch GPM is oil flow in gallons per minute

Metric

Kw = Bar X dm3/min + 600 Kw is power in kilowatts Bar is system pressure dm3?min is flow, cu dm/minute

Velocity of oil flow in pipe

V = GPM X 0.3208 + A V is oil velocity in feet per second GPM is flow in gallons per minute A is inside area of pipe in square inches

Metric

V = dm3/min + 6A V is oil velocity in meters per second dm3/min is oil flow in cubic dm/minute A is inside area of pipe in square centimeters

Charles Law for behaviour of gases

T1V2 = T2V1 or T1P2 = T2P1 T1 P1 and V1 are initial temperature, pressure and volume T2 P2 and V2 are final conditions

Boyles Law for behaviour of gases

P1V1 = P2V2 P1 and V1 are initial pressure and volume P2 and V2 are final conditions

Hydraulic Formulas

Circle Formulas

Area = pi X radius square OR pi X diameter square + 4 Circumference = 2 X pi X radius OR pi X diameter pi = 3.14

Heat equivalent of fluid power

BTU per hour = PSI X GPM X 1.5

Hydraulic cylinder piston speed

S = CIM + A S is piston travel speed, inches per minute A is piston area in square inches

Force or thrust of any cylinder

F = A X PSI F is force or thrust in pounds A is piston net area in square inches PSI is gauge pressure

Metric

N = A X Bar X 10 N is Cylinder force in Newtons A is piston area in square centimeters Bar is gauge pressure

Force for piercing or shearing sheet metal

F = P X T X PSI F is force required in pounds P is perimeter around area to be sheared in inches T is sheet thickness in inches PSI is the shear strength rating of the material in pounds per square inch

Side load on a pump or motor shaft

F = (HP X 63024) + (RPM X R) F is the side load in pounds against shaft R is the pitch radius in inches of sheave on pump shaft HP is driving power applied to shaft

Hydraulic Formulas

Effective force of a cylinder working at an angle to the direction of the load travel

F = T X sin A T is the total cylinder force in pounds F is the part of the force which is effective in pounds A is temperature difference in degrees F between oil and surrounding temperature.

Heat radiating capacity of a steel reservoir

HP = 0.001 X A X TD HP is the power radiating capacity expressed in horsepower A is surface area in square feet TD is temperature difference in degrees F between oil and surrounding air

Burst pressure of pipe or tubing (Barlows Formula)

P = 2t X S + O P is burst pressure in PSI t is wall thickness in inches S is tensile strength of the material in PSI O is outside diameter in inches

Metric

P = 2t X S + O

P is burst pressure in Bar t is pipe wall thickness in mm S is tensile strength pipe material in Bar O is outside diameter of pipe in mm

Relationship between displacement and torque of a hydraulic motor

T = D X PSI + 24 Pi T is the torque in foot pounds D is displacement in cubic inches per revolution PSI is pressure difference across motor pi = 3.14

Travel speed of a hydraulic cylinder piston

S = V + A S is travel speed in inches per minute V is volume of oil to cylinder in inches per minute A is area in square inches

Metric

S= V + A S is travel speed in meter per second V is oil flow in dm3 per minute A is piston area in square centimeters

Hydraulic Formulas

Recommended maximum oil velocity in hydraulic lines

fps = feet per second

Pump suction lines is 2 to 4 fps Pressure lines to 500 PSI is 10 to 15 fps Pressure lines to 3000 PSI is 15 to 20 fps Pressure lines over 3000 psi is 25 fps Oil lines in air/oil system is 4 fps

Metric

Mps = meters per second

Pump suction lines is 0.6 to 1.2 mps Pressure lines to 35 bar is 3 to 4.5 mps Pressure lines to 200 bar is 4.5 to 6 mps Pressure lines over 200 bar is 7.5 mps Oil lines in air/oil systems is 1.25 mps

Considerations

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 its full rating horsepower.

Compressibility of Hydraulic Oil

Volume reduction is approximately ½ % for every 1000 PSI of fluid pressure.

Compressibility of water

Volume reduction is about 1/3% for every 1000 PSI of pressure.

Wattage for heating hydraulic oil

Each watt will raise the temperature of a gallon of oil by 1 degree 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 feet per second pressure lines 500 to 3000 PSI 15 to 20 feet per second pressure lines over 3000 PSI 25 feet per second all oil lines in air over oil system 4 feet per second

Hydraulic Formulas