Hydraulics and Fluid Dynamics Flashcards

A hydraulic system uses oil with a specific gravity of 0.9. Compared to water, the oil weighs:

Answer: 10% less per unit volume

Specific gravity of 0.9 means the oil is 90% as dense as water, so it weighs 10% less per unit volume.

In a hydraulic system, what is 'back pressure'?

Answer: Residual pressure on the return side of an actuator opposing its motion

Back pressure is the pressure that exists in the return line and acts against the moving side of a cylinder, reducing net force.

A check valve is installed in a hydraulic line. What does it do?

Answer: Allows fluid to flow in one direction only

A check valve contains a ball or poppet that blocks reverse flow while allowing free flow in the intended direction.

When a hydraulic hose bursts suddenly, the most immediate danger is:

Answer: High-pressure fluid injection through skin, which can cause severe injury

High-pressure fluid can penetrate skin and cause serious internal injury even through small pinhole leaks.

A hydraulic motor converts:

Answer: Fluid pressure and flow into rotational mechanical output

A hydraulic motor is the reverse of a pump — pressurized fluid enters and drives a shaft to rotate.

Why do hydraulic systems typically use oil rather than water as the working fluid?

Answer: Oil lubricates components and resists corrosion, unlike water

Oil provides necessary lubrication to internal moving parts and does not cause rust or corrosion as water would.

If hydraulic system pressure is measured at 2,000 psi and a cylinder has a 5 sq in piston area, what is the maximum force it can exert?

Answer: 10,000 lbs

Force = Pressure × Area = 2,000 psi × 5 sq in = 10,000 lbs.