Hydraulic Systems Flashcards

What is the purpose of a hydraulic pressure reducing valve?

Answer: To maintain a constant lower pressure in a branch circuit downstream of the main system pressure

A pressure reducing valve maintains a constant, lower pressure in a secondary circuit branch, regardless of fluctuations in the main system pressure. It senses downstream pressure and modulates to keep it at the set value.

Why must hydraulic hose assemblies be replaced if the outer cover shows exposed wire braid?

Answer: Exposed braid means the hose has suffered external damage compromising its burst strength and allowing moisture to corrode the reinforcement

Exposed wire braid indicates that the outer protective cover has been worn through or cut, compromising the hose's rated burst strength. Moisture penetrating to the braid causes corrosion, further weakening the hose and risking catastrophic failure.

What does volumetric efficiency of a hydraulic pump indicate?

Answer: The ratio of actual pump output flow to theoretical output flow, indicating internal leakage

Volumetric efficiency is the ratio of actual output flow to theoretical flow (based on displacement × speed). A decrease in volumetric efficiency indicates increasing internal leakage due to wear, which means the pump delivers less flow for the same speed.

What is the purpose of a sequence valve in a hydraulic circuit?

Answer: To ensure that one actuator completes its stroke before a second actuator begins to move

A sequence valve opens when pressure reaches its set point, indicating that the first actuator has completed its stroke (stalled against its load), then directs flow to the second actuator. This ensures operations occur in the correct order.

What type of hydraulic fluid should never be mixed with petroleum-based hydraulic fluid?

Answer: Water-glycol or phosphate ester fire-resistant fluids

Water-glycol and phosphate ester fire-resistant fluids are chemically incompatible with petroleum-based fluids. Mixing them causes chemical reactions, sludge formation, seal damage, and loss of fire resistance. Different seal materials are required for each type.

How do you test the pre-charge pressure of a bladder accumulator safely?

Answer: Isolate the accumulator, drain the oil side to zero pressure, then check gas pressure with a proper charging kit

To safely check pre-charge, the accumulator must be isolated from the system and the oil side pressure reduced to zero. Then a nitrogen charging kit with a gauge is connected to the gas valve to measure the pre-charge pressure.