Hydraulics

Question 1

Define ‘Hydraulics’

Answer 1

A branch of science and technology about the conveyance of liquids through pipes and channels especially as a source of mechanical force or control

Question 2

Define ‘Pneumatics’

Answer 2

A branch of science or technology about the mechanical properties of gasses.

Question 3

What happens to the fluid in hydraulics?

Answer 3

It is held in a closed system

Question 4

What are the pros of hydraulics?

Answer 4

> Fluids are incompressible so can exert extreme pressures

> Hydraulics consume less energy than pneumatics because pneumatics uses continually replenished gas.

> Hydraulics produce highly defined actions

> Hydraulics are self-lubricating and aid anti-corrosion

Question 5

What are the cons of hydraulics?

Answer 5

Hydraulic fluid is a contaminant and is no suitable for certain applications

Question 6

What are pumps?

Answer 6

Converts mechanical energy into hydraulic energy

Question 7

How do hydraulic pumps work?

Answer 7

> Creates a vacuum at the pump inlet which allows atmospheric pressure to force liquid from the reservoir into the inlet line to the pump.

> Delivers liquid to the pimp outlet and forces it into the hydraulic system

> Balls dictate the direction of liquid flow.

Question 8

What is pressure?

Answer 8

> It does not generate pressure. It produces the flow necessary for the development of the pressure which is a function of resistance to the fluid flow.

Question 9

What is a positive displacement pump?

Answer 9

Delivers the same amount of liquid for each cycle of the pump action. Delivery remains constant regardless to the changes in pressure.

Question 10

What is a variable displacement pump?

Answer 10

Delivers the different amounts of liquid for each cycle of the pump action.

Question 11

List the properties of cylinders?

Answer 11

> Single Port / Dual Port

> Single Acting / Dual Acting

> Returned / Returned by a spring / Returned by an external force

Question 12

What are 4 different activation methods?

Answer 12

> Lever controlled

> Foot controlled

> Push button controlled

> Solenoid controlled

Question 13

List the two types of resevoirs

Answer 13

> Non-pressurised hydrostatic

> Non-pressurised atmospheric

Question 14

List 6 types of valves

Answer 14

> Check valves without spring

> Check valves with spring

> Shut off valve (normally open)

> Shut off valve (normally closed)

> Directional control valves

> Pressure release valves

Question 15

For a direction control valve, what are the 3 different functions it can perform?

Answer 15

> Stop fluid flow

> Allow fluid flow

> Change the direction of fluid flow

Question 16

What is a double acting cylinder?

Answer 16

> Facilitates the exertion of force in either direction.

> Box with the lines that extend out indicate the default state

Question 17

For a pump, what are the 3 different symbols and what do they mean?

Answer 17

> Circle = Motorised

> Triangles = Number of directions of pumping ability (1 or 2 triangles)

> Arrow (from bottom-left to top-right) = Variable displacement [Symbol1]

Question 18

For a cylinder, what are the 3 different symbols and what do they mean?

Answer 18

Lines (coming out from the side) = Ports

Spring = Returned by spring

Lever/Foot/Push-button/Solenoid = Control method [Symbol2]

Question 19

What is the symbol for non-pressurised hydrostatic?

Answer 19

[Symbol3]

Question 20

What is the symbol for non-pressurised atmospheric?

Answer 20

[Symbol4]

Question 21

What is the symbol for a check valve?

Answer 21

[Symbol5]

Question 22

What is the symbol for a check valve with a spring?

Answer 22

[Symbol6]

Question 23

What is the symbol for a normally open shut off valve?

Answer 23

[Symbol7]

Question 24

What is the symbol for a normally closed shut off valve?

Answer 24

[Symbol8]

Question 25

Draw a directional control valve, normally closed, 2 ports 2 positions with spring return and level control

Answer 25

[Symbol9]

Question 26

Draw a directional control valve, normally open, 2 ports 2 positions with spring return and button control

Answer 26

[Symbol10]

Question 27

Draw a directional control valve, normally closed, 2 ports 2 positions with spring return and solenoid control

Answer 27

[Symbol11]

Question 28

What is the symbol for automatic valves (pressure relief)

Answer 28

[Symbol12]

Question 29

What are the 4 parameters of a cylinder?

Answer 29

\> Bore: The diameter of the internal chamber \> Rod: The diameter of the piston rod \> Stroke: The distance the piston will travel \> Pressure: The maximum hydraulic pressure allowed

Question 30

How is PSI calculated? What is the equation?

Answer 30

PSI = Force (lb) / Surface area (in²)

Question 31

What is the equation to calculate the force applied to the side of the piston without the rod?

Answer 31

F_A = P_Sπr²

Question 32

What is the equation to calculate the force applied to the side of the piston with the rod?

Answer 32

F_B = P_Sπ(C_D² - R_D²) / 4

Question 33

How is the distance that the rod moves based on the volume of fluid calculated on the rodless side?

Answer 33

R_TD = V / πr²

Question 34

How is the distance that the rod moves based on the volume of fluid calculated on the rod side?

Answer 34

R_TD = 4V / π(C_D² - R_C²)

Question 35

What happens when there are two pistons in parallel with diffent weights?

Answer 35

\> The lighter piston moves first \> When the ligher piston is fully extended, the heavier one moves \> When the heavier piston is fully extended, the pressure release valve is activated [Picture25]

Question 36

What happens when you have pistons in series?

Answer 36

\> Regardless of weight, the first piston moves until it is fully extended \> When fully extended, the second piston moves