Hydraulic & Pneumatic Systems Flashcards

In a hydrostatic transmission, what component varies the displacement to change output speed and direction?

Answer: Variable displacement piston pump

A variable displacement piston pump adjusts swashplate angle to change flow volume and direction, directly controlling motor speed and rotation direction without mechanical gearing.

Which hydraulic valve function is described as 'normally open, pilot-to-close'?

Answer: A pilot-operated check valve allowing free flow until pilot pressure closes it

A normally-open pilot-operated check valve permits free flow in its normal state but blocks flow when pilot pressure is applied, used for clamping or locking circuits.

Bernoulli's principle applied to hydraulic flow through a restriction means that:

Answer: Pressure decreases as flow velocity increases through a constriction

Bernoulli's principle states that in a flowing fluid, increased velocity at a restriction is accompanied by decreased static pressure, the basis for flow meter operation.

What distinguishes an electrohydraulic servo valve (EHSV) from a standard proportional valve?

Answer: EHSVs use mechanical feedback for extremely precise position control with minimal hysteresis

Servo valves incorporate mechanical or electrical feedback (torque motor + flapper nozzle) providing sub-millisecond response and hysteresis below 1%, far exceeding proportional valve accuracy.

In a pneumatic vacuum system using a venturi generator, vacuum is created by:

Answer: Compressed air flowing through a nozzle creating low pressure by Bernoulli effect

A venturi vacuum generator passes compressed air through a converging nozzle; the high-velocity jet creates a low-pressure zone at the side port, drawing in surrounding air to create vacuum.

When sizing hydraulic tubing, the maximum recommended fluid velocity for pressure lines is typically:

Answer: 5–10 ft/sec

Hydraulic pressure lines are typically sized for 10–15 ft/sec maximum to limit pressure losses and turbulence, with return lines kept below 10 ft/sec.

A counterbalance valve in a vertical hydraulic press circuit is primarily used to:

Answer: Prevent the load from descending uncontrolled if a line ruptures

A counterbalance valve maintains back-pressure on the rod side of a vertical cylinder, preventing load-induced runaway descent and providing safety if supply pressure is lost.