Introduction to Fluid Power

by

Mike Pierno

Pascal’s Law, simply stated, says this:

Pressure applied on a confined fluid is transmitted undiminished in all directions, and acts with equal force on equal areas and at right angles to them.

F = P x A

Pascal’s Law

HOW PRESSURE IS CREATED

Pressure results whenever there is a resistance to

fluid flow or to a force which attempts to make the

fluid flow. The tendency to cause flow (or the push)

may be supplied by a mechanical pump, compressor,

or may be caused simply by the weight of the fluid.

Atmospheric pressure is a “head” of air.

Pressure “head” comes from the weight of the fluid.

Force is Proportional to Pressure and Area

These Pressure, Force and Area relationships are sometimes illustrated as shown below to aid in remembering the equations.

F = P x A

P = F / A

A = F / P

When a cylinder is used to clamp or press, its output force can be computed as follows:

F = P x A

Again:

P is Pressure (PSI (Bar) (Pascals))

F is Force (pounds (newtons))

A is Area (Square inches (Square meters)

P A

F

Simple Mechanical Lever

Simple Hydraulic Lever

141.3

141.3

141.3

141.3

Parallel Flow PathsList the order in which the cylinders will extend, and calculate the pressure needed to lift the load for each.

A B C

4” bore 2” bore 6” bore

Sequence

1st

2nd

3rd

PSICyl.

24,000 lbs. 24,000 lbs. 24,000 lbs.

Series Resistance and Pressure

Bernoulli’s PrincipleBernoulli’s Principle states that if the flow rate is constant, the sum of the kinetic ands pressure energy must be constant. Therefore, if the kinetic energy decreases, it must result in an increased pressure. Likewise, when the cross-sectional area of the flow path decreases, the kinetic energy (velocity) produces a corresponding decrease in pressure.

Laminar flow is in parallel paths.

Turbulence results in flow resistance.

Velocity is inversely proportional to pipe cross-sectional area

Introduction to Fluid Power

by

Mike Pierno