Formulas

T = HP x 5252 ÷ RPM

HP = T x RPM ÷ 5252

RPM = HP x 5252 ÷ T

Torque and Horsepower Relations

*Torque values are in foot pounds.

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

Charles’ Law for Behavior of Gases

T1V2 = T2V1, or T1P2 = T2P1

* T1, P1 and V1 are initial temperature, pressure and volume
* T2, P2 and V2 are final conditions.

T = HP x 5252 ÷ RPM

HP = T x RPM ÷ 5252

RPM = HP x 5252 ÷ T

Hydraulic (Fluid Power) Horsepower

* PSI is gauge pressure in pounds per square inch
* GPM is oil flow in gallons per minute

Circle Formulae

Area = πr², or πD² ÷ 4
Circumference = 2πr, or πD

* r is radius
* D is diameter, inches
* π is 3.14

Heat Equivalent of Fluid Power

BTU per hour = PSI x GPM x 1½

S = CIM ÷ A

Hydraulic Cylinder Piston Travel Speed

* S is piston travel speed, inches per minute
* CIM is oil flow into cylinder, cubic inches per minute
* A is piston area in square inches

Thrust or Force of Any Cylinder

T = A x PSI

* T is thrust or force, in pounds
* A is piston area, in square inches
* PSI 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 sheer strength rating of the material in pounds per square inch

F = (HP x 63024) ÷ (RPM x R)

Side Load on Pump/ Motor Shaft

* F is the side load, in pounds, against shaft
* R is the pitch radius of sheave on pump shaft, in inches
* HP is driving power applied to shaft

Effective Force of a Cylinder working at an Angle to Direction of the Load Travel

T = A x PSI

* T is thrust or force, in pounds
* A is piston area, in square inches
* PSI is gauge pressure

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 °F between oil and surrounding air

Heat Radiating Capacity of a Steel Reservoir

Burst Pressure of Pipe or Tubing

P = 2t x S ÷ O

* P is burst pressure in PSI
* t is wall thickness, in inches
* S is tensile strength of material in PSI
* O is outside diameter, in inches

Relationship between Displacement and Torque of a Hydraulic Motor

T = D x PSI ÷ 24π

* T is torque in foot pounds
* D is displacement in cubic inches per revolution
* PSI is pressure difference across motor
* π is 3.14

Hydraulic Tank Volume & Fill (Gallons)

(Height (h) X Width (w) X Length (l))/231 = Capacity in Gallons

* Measurements in inches

Torque, HP, Speed Relations in Hydraulic Pumps and Motors

T = HP x 5252 ÷ RPM
HP = T x RPM ÷ 5252
RPM = HP x 5252 ÷ T

English Units

* T = Torque, foot-lbs.
* RPM = Speed, revs/min
* HP = Horsepower

Metric Units

T = Kw x 9543 ÷ RPM
Kw = T x RPM ÷ 9543
RPM = Kw x 9543 ÷ T

* T = Torque, Nm (Newton-meters)
* RPM = Speed, revs/min
* Kw = Power in kilowatts

Hydraulic Power Flowing Through the Pipes

HP = PSI x GPM ÷ 1714

English Units

* HP = Horsepower
* PSI = Gauge pressure, lbs/sq. inch
* GPM = Flow, gallons per minutes

Metric Units

Kw = Bars x dm³/min ÷ 600

* Kw = Powers in kilowatts
* Bars = System pressure
* dm³/min = Flow, cu. dm/minute

Force Developed by an Air or Hydraulic Cylinder

T = A x PSI

English Units

* T = Force or thrust, in lbs.
* A = Piston area, square inches
* PSI = Gauge pressure, lbs/sq. inch

Metric Units

N = A x Bars x 10N = Cylinder force in Newtons

* A = Piston area, sq. centimeters
* Bars = Gauge pressure

Travel Speed of a Hydraulic Cylinder Piston

S = V ÷ A

English Units

* S = Travel speed, inches/minute
* V = Vol. of oil to cyl., cu.in/min
* A = Piston area, square inches

Metric Units

S = V ÷ 6A

* S = Travel speed, meter/sec
* V = Oil flow dm³/minute
* A = Piston area, square centimeters

Barlow’s Formula - Burst Pressure of Pipe & Tubing

P = 2t x S ÷ O

English Units

* P = Burst pressure, PSI
* T = Pipe wall thickness, inches
* S = Tensile str., pipe material, PSI
* O = Outside diameter of pipe, inches

Metric Units

P = 2t x S ÷ O

* P = Burst pressure, bars
* T = Pipe wall thickness, mm
* S = Tensile str., pipe material, bars
* O = Outside diameter of pipe, mm

Velocity of Oil Flow in Hydraulic Lines

V = GPM x 0.3208 ÷ A

English Units

* V = Velocity, feet per second
* GPM = Oil flow, gallons/minute
* Velocity of an oil flow in pipe
* “GPM is oil flow in gallons per minute” = Inside area of pipe, sq. inches

Metric Units

V = dm³/min ÷ 6A

* V = Oil velocity, meters/second
* dm³/min = Oil Flow, cu.dm/minute
* A = Inside area of pipe, sq.cm

Recommended Maximum - Oil Velocity in Hydraulic Lines

fps = feet per second
Pump suction lines – 2 to 4 fps
Pres. lines to 500 PSI – 10 to 15 fps
Pres. lines to 3000 PSI – 15 to 20 fps
Pres. lines over 3000 PSI – 25 fps
Oil lines in air/oil system – 4 fps

English Units

Metric Units

mps = meters per second
Pump suction lines – .6 to 1.2 mps
Pres. lines to 35 bar – 3 to 4½ mps
Pres. lines to 206.8 bar – 4½ to 6 mps
Pres. lines over 200 bar – 7½ mps
Oil lines in air/oil system – 1¼ mps

Rules of Thumb

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 rated horsepower.

Compressibility of Hydraulic Oil

Volume reduction is approximately 0.5% for every 1000 PSI pressure.

Compressibility of Water

Volume reduction is about 0.3% for every 1000 PSI pressure.

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/second
Pressure Lines up to 500 PSI: 10 to 15 feet/second
Pressure Lines 500 to 3000 PSI: 15 to 20 feet/second
Pressure Lines over 3000 PSI: 25 feet/second
All Oil Lines in Air-Over-Oil System: 4 feet/second