Mechanical Aptitude Hydraulics and Pneumatics Flashcards

A 4/2 directional control valve has:

Answer: 4 ports and 2 positions

Valve notation lists ports first, then positions, so a 4/2 valve has 4 ports and 2 switching positions.

What does a pressure relief valve do when system pressure reaches its set point?

Answer: Opens to divert fluid back to the reservoir

A relief valve opens at its set pressure to bypass excess fluid back to tank, protecting the system from overpressure.

Boyle's Law states that for a fixed mass of gas at constant temperature, pressure and volume are:

Answer: Inversely proportional

Boyle's Law states P₁V₁ = P₂V₂: as pressure increases, volume decreases proportionally when temperature stays constant.

Which seal type is most commonly used to prevent fluid leakage in hydraulic cylinder rods?

Answer: U-cup (lip seal)

U-cup lip seals are the most common rod seal because they provide excellent dynamic sealing as the rod moves in and out.

In a pneumatic system, what is the typical maximum working pressure compared to a hydraulic system?

Answer: Pneumatic pressure is typically much lower

Pneumatic systems typically operate at 80–150 PSI, while hydraulic systems routinely work at 1,000–5,000 PSI or higher.

What is the main advantage of a hydraulic system over a pneumatic system for heavy lifting?

Answer: Hydraulic systems can generate much greater forces due to higher operating pressures

Because hydraulic fluid operates at much higher pressures than compressed air, hydraulic systems can produce far greater forces for heavy-duty applications.

What happens to the speed of a hydraulic cylinder if pump flow rate is doubled while load remains the same?

Answer: Speed doubles

Cylinder speed is directly proportional to flow rate entering it, so doubling the flow doubles the piston velocity.