S Hydraulic Systems

Question 1

What is a single acting actuator?

Answer 1

Hydraulic pressure moves the piston in 1 direction only, a spring supplies the return force

Question 2

Wha is a double acting balanced actuator?

Answer 2

Hydraulic pressure can move the piston in either direction with equal force

Question 3

What is a double acting unbalanced actuator?

Answer 3

Hydraulic pressure can move the piston in either direction, but different forces will be generated in each direction

Question 4

What is a non-return/check valve?

Answer 4

Allow fluid to flow in 1 direction only

Question 5

What is a selector valve?

Answer 5

Can direct fluid to various parts of the system

Question 6

Why is a hydraulic reservoir pressurised?

Answer 6

To prevent boiling

Question 7

What are the 5 uses of accumulators?

Answer 7

1. Store energy to keep fluid under pressure
2. Provided limited supply in an emergency
3. Dampen pressure fluctuations
4. Allows thermal expansion
5. Cater for small internal leaks

Question 8

What is an automatic cut off valve (ACOV)?

Answer 8

When system pressure increases above a pre set level a valve opens to create an idling circuit

Question 9

What drives a hydraulic pump?

Answer 9

Engine

Question 10

What is a hydraulic motor?

Answer 10

Uses hydraulic pressure to generate rotary motion

Question 11

Where is the hydraulic filter located?

Answer 11

Downstream of the hydraulic pump

Question 12

What happens if the hydraulic filter becomes clogged?

Answer 12

• Red filter pop out button or cockpit warning light

- Bypass valve automatically allows unfiltered fluid to flow past blocked filter

Question 13

What does a pressure relief valve do?

Answer 13

Protects system from over pressurisation

Question 14

What does a thermal relief valve do?

Answer 14

Dumps excess pressure due to heat inducted expansion

Question 15

Where does the relief valve send fluid?

Answer 15

Back to the reservoir

Question 16

What is a restrictor valve (choke valve)?

Answer 16

Reduces fluid flow to slow the speed of operation of a service

Question 17

What is a priority valve?

Answer 17

Ensures sufficient fluid flow at all times to the primary controls and wheel brakes

Question 18

What is a shuttle valve?

Answer 18

Allows one service to be operated by 2 independent supplies, selects the most appropriate supply

Question 19

What is a hydraulic fuse?

Answer 19

• Located upstream of components
• Prevents fluid loss in the event of a major leak
• If flow becomes too great, pressure drops behind the piston and forces it to close

Question 20

What is a shut-off valve?

Answer 20

Stops hydraulic flow to a service, therefore stopping it, is not self regulating so needs to be operated by a controller

Question 21

What is a PTU?

Answer 21

Power transfer unit, uses one system to pressurise another

Question 22

Why is it important to monitor hydraulic temperature?

Answer 22

Excess temp reduces viscosity and lubrication

Question 23

What 3 parameters of the hydraulic system are monitored?

Answer 23

• Temperature
• Pressure
• Quantity