What fluid power is
Before any formula: what a "power system" does, where hydraulics sits among the choices, and the one idea the whole course is built on — pressure does the work.
Source: Rabie, Fluid Power Engineering, Ch. 1.
Before you start
What you need first
- Nothing — this is the very first topic. Just curiosity about how machines make force and motion.
What you'll be able to do
- Say what a power system is and name its three parts.
- Tell apart the four families — mechanical, electrical, pneumatic, hydraulic.
- Explain what hydrostatic hydraulics is and why we choose it.
Start here · the big picture
A power system moves and shapes power
A power system takes power in at one place and delivers useful motion at another — carrying it, transforming it, and controlling it along the way.
Four families of power systems
There are four ways to carry power from the source to the load. Each is good at something different.
The four, side by side
No family wins everywhere — each is chosen for what it is best at.
| Property | Mechanical | Electrical | Pneumatic | Hydraulic |
|---|---|---|---|---|
| Power-to-weight | Poor | Fair | Good | Best |
| Stiffness (holds a load still) | Good | Poor | Fair | Best |
| Long-distance transmission | Poor | Best | Good | Good |
| Control & flexibility | Fair | Best | Good | Good |
| Motion type | Rotary | Rotary | Both | Both |
After Table 1.1 (simplified). Examples: mechanical = a car drivetrain; electrical = the power grid; pneumatic = an air wrench; hydraulic = a forklift or excavator.
Two kinds of hydraulic — we use one
Hydraulic systems use a liquid (oil) to carry power. There are two kinds:
- Hydrodynamic — power is carried by the oil's speed (kinetic energy). Example: a car's torque converter.
- Hydrostatic — power is carried by the oil's pressure. This is our course.
Where these ideas come from
Two old discoveries sit under this whole course. In 1647, Blaise Pascal found that pressure in a trapped fluid spreads equally in every direction — that becomes Pascal's law in the next topic, and it is why a small pump can lift a heavy load. In 1738, Daniel Bernoulli set out the conservation of energy — the rule that a machine can multiply force but never create energy, which we use directly in Topic 2.
Why choose hydraulics — and when not
✏️ Try it yourself
Which family does each machine use — mechanical, electrical, pneumatic, or hydraulic?
- A bicycle's chain and gears
- The electricity grid feeding a factory
- An air wrench in a tyre shop
- A forklift lifting a pallet with oil pressure
Recap — the whole topic on one screen
| Idea | What you own now |
|---|---|
| Power system | Source → transmission & control → load |
| Four families | Mechanical, electrical, pneumatic, hydraulic |
| Our course | Hydrostatic hydraulics — power carried by oil pressure |
| The one idea | The pump squeezes the oil; the pressure does the work |