Mechanical Aptitude Mechanical Aptitude Hydraulics and Pneumatics 4

Question 1

A 4/2 directional control valve has:

Accepted Answer

4 ports and 2 positions

Answer

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

Question 2

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

Accepted Answer

Opens to divert fluid back to the reservoir

Answer

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

Question 3

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

Accepted Answer

Inversely proportional

Answer

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

Question 4

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

Accepted Answer

U-cup (lip seal)

Answer

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

Question 5

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

Accepted Answer

Pneumatic pressure is typically much lower

Answer

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

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