**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

Return from Hydraulic Formulas to Home Page

Return from Hydraulic Formulas to Explain Hydraulics

Hard copy and E book for sale. Introduction to Building Mechanical Systems. Click here.