In hydraulic and pneumatic control systems, which statement is true?

• A. Hydraulic uses incompressible fluid to transmit power; Pneumatic uses compressed gas
• B. Hydraulic uses compressible gas to transmit power; Pneumatic uses incompressible fluid
• C. Hydraulic uses only electricity
• D. Pneumatic uses hydraulic fluid

Answer: (A)

In hydraulic and pneumatic control systems, the way pressure is transmitted depends on the fluid’s properties. Hydraulic systems use a liquid, typically oil, which behaves almost incompressibly. When you apply pressure, it is transmitted through the liquid with little volume change, so a small movement in the hydraulic line can generate a large force at the actuator. This is why hydraulics are favored for high-force, precise control.

Pneumatic systems use a gas, usually air, which is compressible. The fluid’s compressibility means pressure can build by compressing the gas, storing energy in the form of increased pressure and volume. This leads to softer, more forgiving motion with rapid response but generally lower force compared to hydraulics.

So the true statement is that hydraulic uses incompressible fluid to transmit power, while pneumatic uses compressed gas. The other options mix up these properties or introduce electricity or hydraulic fluid as the working medium, which don’t fit how these systems operate.