Ramsay Hydraulics & Pneumatics Flashcards

A hydraulic intensifier has a large input piston with an area of 20 in² and a small output piston with an area of 4 in². If 500 psi is applied to the large piston, what output pressure will the small piston generate?

Answer: 2,500 psi

A hydraulic intensifier multiplies pressure by the ratio of the input area to the output area. P_out = P_in × (A_large / A_small) = 500 × (20 / 4) = 500 × 5 = 2,500 psi. The trade-off is that flow rate is reduced by the same ratio.

A hydraulic system suddenly develops a rattling noise and the pump begins eroding internally. Operating temperature is normal and fluid level is adequate. What is the MOST likely root cause?

Answer: Suction line restriction causing cavitation at the pump inlet

Cavitation occurs when inlet (suction) pressure falls below the fluid's vapor pressure, typically due to a restricted or undersized suction line, a clogged inlet strainer, or fluid that is too cold and viscous. Vapor bubbles form and then violently implode, causing the characteristic rattling noise and rapid erosion of pump internals. High back-pressure, relief valve setting, and check valve wear do not cause cavitation.

A bladder-type hydraulic accumulator is pre-charged with nitrogen to 1,000 psi. System maximum pressure is 3,000 psi and minimum working pressure is 1,500 psi. At what system pressure will the accumulator STOP delivering fluid to the circuit?

Answer: 1,000 psi

An accumulator delivers stored fluid as long as system pressure is higher than the gas pre-charge pressure. Once system pressure drops to the pre-charge level (1,000 psi), the bladder or diaphragm is fully expanded and no more fluid can be expelled — the accumulator is empty. It stops delivering at pre-charge pressure, not at the minimum working pressure.

A counterbalance valve is installed in the rod-side line of a hydraulic cylinder supporting a heavy vertical load. If the upstream supply hose ruptures during a hold cycle, what will the counterbalance valve do?

Answer: Block rod-side flow and prevent the load from free-falling

A counterbalance valve maintains a set back-pressure on the rod side that exceeds the load-induced pressure. If the upstream supply line ruptures, pressure at the valve's pilot port drops to zero, so the valve snaps shut and blocks rod-side flow — preventing the load from free-falling. It will only open (in the controlled direction) when positive pilot pressure from the cap-side supply exceeds its set point.

A pneumatic venturi vacuum generator uses 80 psi shop air flowing through a converging nozzle. Which statement CORRECTLY describes conditions at the throat of the venturi?

Answer: Velocity increases and static pressure decreases, generating a partial vacuum

By Bernoulli's principle, in a flowing fluid total energy is conserved. At the venturi throat, the flow area is smallest, so air velocity must increase to maintain continuity. As kinetic energy (velocity) increases, static pressure energy must decrease — dropping below atmospheric pressure and creating a vacuum at the side port. This is the operating principle of ejectors and vacuum cups in pneumatic systems.

A priority flow divider valve is set to supply exactly 6 GPM to a power steering circuit (Circuit A). The hydraulic pump delivers 14 GPM at operating speed. A technician then throttles the return line on Circuit B with a needle valve, increasing its back-pressure significantly. What happens to flow in Circuit A?

Answer: Circuit A flow remains at 6 GPM because the priority divider is pressure-compensated

A priority (pressure-compensated) flow divider maintains constant priority flow to Circuit A regardless of downstream load changes in either circuit — that is its design purpose. It achieves this by sensing and compensating for pressure variations. Throttling Circuit B raises that branch's pressure, but the divider's compensator spool automatically adjusts to keep Circuit A at its set 6 GPM. Only if pump output itself drops below 6 GPM would Circuit A be affected.