Fluid Power, Hydraulics Formula Equations

Hydraulic and Pneumatic Knowledge
Fluid Power Equipment

The following are equations for Fluid Power applications, Fluid Velocity on a pipe, Charles Law, and more.

Torque and Horsepower Relations:

T=(HP x 5252)/RPM
HP= (T x RPM)/5252
RPM = (HP x 5252)/T

Torque is FT-LBS

Hydraulic Fluid Power horsepower:

V = (GPM x PSI)/ 1714

PSI is gauge pressure in in pounds per square inch
GPM is oil flow in Gallons per minute.

Fluid Power Velocity of oil flow in pipe:

V =(GPM x .3208) /A

Z 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, and T2, P2, and V2 are final conditions

Boyle's Law for behavior of gasses:

P1V1 = P2V2

P1 and V1 are initial pressure and volume; P2 and V2 are final conditions.

Heat equivalent of fluid power:

BTU per hour = PSI x GPM x 1.5

Hydraulic cylinder piston travel speed:

S = CIM / A

S is thrust of force, in pounds
A is piston net area in square inches
PSI is gauge pressure.
CIM is oil flow into cylinder, cubic inches per minute

Side load on 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 the driving power applied to shaft

Effective force of a cylinder working at an angle to 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
A is the least angle, in degrees between cylinder axis and load direction

Heat radiating capacity of a steel reservoir:

HP = .001 x A x TD


HP = Power radiating capacity expressed in horsepower
A = Surface area, in square feet
TD = Temperature difference in deg. F between oil and surrounding air.

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, inches

Relationship between displacement and torque of a hydraulic motor:

T = (PSI x D)/ (24 x 3.14157)

T is torque in foot - lbs
D is displacement in cubic inches per revolution
PSI is pressure difference across motor

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