Hydraulic Systems

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Questions and Answers

What is the primary purpose of a 'cut-out' in a hydraulic system?

To prevent fluid leakage during pipe fractures

To allow continuous pressure to essential systems during reduced supply

To relieve pump load when services are complete and the accumulator is charged (correct)

To dampen pressure surges in the system

How can hydraulic pressure be restored in a system?

By compressing fluid in the reservoir

By using a pressure/heat exchanger

By compressing the air charge in an accumulator (correct)

By increasing pump speed

What is the color of the band on a hydraulic seal?

White

Green (correct)

Red

Yellow

What is the function of a maintainer valve in a hydraulic system?

To allow continued pressure to essential systems during reduced supply Signup and view all the answers

In a hydraulic system, what component prevents creep in jack-operated services with multiple positions?

Cut-out Signup and view all the answers

What is the purpose of a 'cut-out' in limiting fluid loss during a pipe fracture?

It is a secondary purpose Signup and view all the answers

Where is the temperature overheat switch located in a hydraulic pump?

In the case drain Signup and view all the answers

What happens if a component has an internal hydraulic leak?

Increase in fluid temperature Signup and view all the answers

What happens to hydraulic fluid when it is overheated?

Increase acidity Signup and view all the answers

How is the hydraulic pump depressurising solenoid actuated?

Energised Closed for fail-safe Signup and view all the answers

How do you prevent hydraulic fluid frothing?

By pressurising Signup and view all the answers

Accumulators as fitted to aircraft hydraulic systems...

store fluid under pressure Signup and view all the answers

A Skydrol hydraulic fluid seal would be made of...

butyl rubber, ethylene propylene or Teflon Signup and view all the answers

Synthetic hydraulic fluid subjected to overheating is high in...

acidity Signup and view all the answers

A normal hydraulic system will...

show pressure and source of hydraulics Signup and view all the answers

A constant volume hydraulic system uses what to relieve pressure in the system when no services are being used?

ACOV Signup and view all the answers

What is the purpose of using two spanners to stop a pipe from twisting?

To secure pipe connections Signup and view all the answers

How is air removed from hydraulic fluid?

Pass over a tray Signup and view all the answers

What is the function of a pressure control relay in a hydraulic pump?

De-energised to start the pump Signup and view all the answers

How is the output of a constant delivery pump varied?

By regulators Signup and view all the answers

What does a check flow valve in a hydraulic system prevent?

Reverse flow Signup and view all the answers

When does an hydraulic de-pressurising valve get energised?

When selected off Signup and view all the answers

In a closed hydraulic system, what happens at the selector valves when no functions are required?

Pressure is maintained at the selector valves at all times Signup and view all the answers

What components constitute a hydraulic power pack?

Reservoir, pump, selector valve, filter Signup and view all the answers

What is one possible issue if an accumulator loses air pressure?

Rapid depressurisation of system Signup and view all the answers

For what purpose would you fit a thermal relief valve in an hydraulic system?

Relieve excess pressure Signup and view all the answers

What is the correct fluid to use in aircraft hydraulic systems?

Only the specified fluid Signup and view all the answers

What are the essential components of a hydraulic system of the constant delivery type?

Accumulator and automatic cut-out valve Signup and view all the answers

What is the primary function of an automatic cut-out valve in a hydraulic system?

Prevent hydraulic lock formation Signup and view all the answers

Why is a maintaining valve fitted to a hydraulic system?

Ensure a supply of fluid to essential services in case of system failure Signup and view all the answers

What is the purpose of a thermal relief valve in a hydraulic system?

Senses fluid pressure Signup and view all the answers

How are hydraulic systems typically flushed?

The same type of fluid as used in the system Signup and view all the answers

What kind of seals are required for Phosphate Ester hydraulic fluid?

Butyl Rubber Signup and view all the answers

What is the primary purpose of a RAT hydraulic pump?

Flying controls if hydraulic power lost. Signup and view all the answers

Where does the hydraulic hand-pump fluid supply usually come from?

The bottom of the reservoir. Signup and view all the answers

Why are hand pumps in hydraulic systems typically double-acting?

Double acting. Signup and view all the answers

What is the purpose of a shuttle valve in a hydraulic system?

Changing over from main to auxiliary system in case of failure Signup and view all the answers

Why are restrictor valves used in a hydraulic system?

To control the rate of system operation Signup and view all the answers

What is the purpose of a non-return valve in a hydraulic system?

Direct fluid to the hydraulic actuator Signup and view all the answers

Why are the end fittings on a non-return valve different?

To prevent incorrect installation Signup and view all the answers

In a hydraulic accumulator, what happens when the hydraulic system pressure reaches 3000 PSI?

It remains at 3000 PSI Signup and view all the answers

What causes automatic cut-out valve hammering in a hydraulic system?

Low accumulator pressure Signup and view all the answers

Why are hand pumps in a hydraulic system usually single-cylinder double-acting?

Two non-return valves are fitted Signup and view all the answers

During a leak test of an hydraulic system, what should the system pressure be?

Maximum pressure Signup and view all the answers

What is required for constant delivery hydraulic pumps in a system?

An automatic cut-out valve and accumulator Signup and view all the answers

Where are pressure relay valves fitted in a hydraulic system?

Before a pressure gauge Signup and view all the answers

Study Notes

Hydraulic Pump and System Components

The temperature overheat switch in a hydraulic pump is located in the case drain.
A component with an internal hydraulic leak will result in an increase in fluid temperature.

Hydraulic Fluid Properties

Overheating hydraulic fluid will increase its acidity.
Synthetic hydraulic fluid subjected to overheating is high in acidity.

Hydraulic System Operation

Hydraulic systems normally operate at 3000 PSI.
A normal hydraulic system will show pressure and source of hydraulics.
When no services are being used, a constant volume hydraulic system uses an Accumulator Charge Valve (ACOV) to relieve pressure in the system.

Hydraulic Pump Types

A fixed volume axial pump contains a drive shaft, swash plate, and cylinder block.
A variable angled pump starts at maximum stroke.

Hydraulic System Components

A duplex seal consists of a rubber 'T' section ring sandwiched between two Teflon rings.
A shuttle valve is used to change over from main to auxiliary system in the case of failure.
A restrictor valve is used to control the rate of system operation.
A mechanical sequence valve is used to ensure the operation of landing gear and doors.