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HYDRAULICS Flashcards

(67 cards)

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1
Q

What factors affect pressure in hydraulics?

A

Depth of the water and height (head) of the nozzle and pump above or below the water source

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2
Q

What is the relationship between pressure and head?

A

Pressure from head is independent of the amount of water and the shape of the container

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3
Q

What happens to pressure as water flows along a hose?

A

Pressure drops due to height of the nozzle above the pump and friction loss

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4
Q

What must the pump operator provide to overcome losses in pressure?

A

The correct pressure at the pump

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5
Q

Define pressure in the context of hydraulics.

A

The force acting on a given surface area

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6
Q

What are the basic units of pressure measurement?

A
  • Bars
  • Newtons
  • Pascals
  • Kilopascals
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7
Q

Which unit of pressure does AFS use and why?

A

Kilopascals because bars, newtons, and pascals are very small units of pressure

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8
Q

What is a kilopascal (kPa) in relation to pascals?

A

1000 pascals

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9
Q

Convert 1 bar to kilopascals.

A

100 kilopascals

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10
Q

What is the atmospheric pressure at sea level in kilopascals?

A

101.32 kPa

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11
Q

What principles of pressure are important at AFS?

A
  • Perpendicular pressure
  • Static pressure
  • How pressure is transmitted
  • Effects of depth and density of a liquid on pressure
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12
Q

What directly affects the water pressure that can be achieved at the nozzle?

A

Depth and density of a liquid

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13
Q

What is perpendicular pressure?

A

Perpendicular pressure is pressure that acts at right angles to any surface on which it acts.

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14
Q

What is static pressure?

A

Static pressure is the stored energy available to force water through pipes, hoses, and valves. When no water is flowing, static pressure is exerted at the same pressure in all directions.

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15
Q

What is pressure transmission?

A

External pressure applied to a static fluid in a container is transmitted equally in all directions.

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16
Q

How is pressure related to depth in a fluid?

A

The downward pressure of a fluid in an open container is proportional to its depth.

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17
Q

What is the pressure at a depth of 1 meter if P = 30 kPa?

A

30 kPa

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18
Q

What is the pressure at a depth of 1 meter if P = 20 kPa?

A

20 kPa

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19
Q

What is the pressure at a depth of 1 meter if P = 10 kPa?

A

10 kPa

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20
Q

How does pressure relate to fluid density?

A

Pressure from a denser liquid, such as mercury, is greater than the pressure from a less dense liquid, such as water.

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21
Q

What is the pressure exerted by 2m of water head?

A

P = 20 kPa

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22
Q

Does the shape of the container affect downward pressure?

A

No, the same depth of water will exert the same downward pressure, irrespective of the shape of the container.

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23
Q

What is the downward pressure at 1m depth?

A

P = 20 kPa

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24
Q

What is jet reaction?

A

Jet reaction is the kickback that occurs when water is discharged from the nozzle, pushing in the opposite direction to the flow.

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25
What can happen if jet reaction is not controlled?
If not controlled, jet reaction can whip the hose around at high speed, posing a serious threat of injury and damage.
26
How can a pump operator minimize jet reaction?
A pump operator can minimize jet reaction by opening and closing delivery valves slowly, operating the throttle to adjust pressure slowly, and achieving optimum nozzle pressures.
27
What should nozzle operators do to control jet reaction?
Nozzle operators can position a backup firefighter behind them, lay the hose flat and straight, and reduce nozzle output if necessary.
28
When does jet reaction most commonly occur?
Jet reaction most commonly occurs when valves are opened too quickly.
29
Why is jet reaction especially dangerous?
Jet reaction is especially dangerous on uneven or wet ground or in precarious situations.
30
What effect does increased water flow have on jet reaction?
The hose kickback effect of jet reaction is greater as the water flow increases, which can knock firefighters off their feet if taken by surprise.
31
What is head in pump operation?
Head is the difference in height in metres between the pump outlet and the nozzle where the water is delivered.
32
What is head loss?
Head loss occurs when water flows uphill, requiring more pressure to overcome gravity.
33
What is head gain?
Head gain occurs when the nozzle is lower than the pump, requiring less pressure to send water downhill.
34
How do you calculate head?
Use the formula: Head (H) = Pressure (P) ## Footnote Head loss/gain is the difference in height (in metres) between the pump outlet and the nozzle.
35
What is suction or vertical lift?
Suction or vertical lift is the maximum height you can draw water from the source to the eye of the pump.
36
What is the theoretical maximum suction lift?
The theoretical maximum suction lift is 10 m, but the practical maximum is about 7.5 m.
37
What is barrier height?
Barrier height is the maximum height a pump is capable of delivering to.
38
How does nozzle height affect pressure?
Add 10 kPa of pressure for every metre the nozzle sits higher than the pump; subtract 10 kPa for each metre the nozzle is below the pump.
39
What is the formula for pressure due to head?
Pressure due to head P = H x 10 ## Footnote (P = pressure. H = head in metres)
40
How do you calculate head from pressure?
H = P / 10 ## Footnote (Pressure in kPa = H x 10 = head or height in metres)
41
What is the standard air pressure at sea level?
The standard air pressure at sea level is approximately 100 kPa.
42
What acronym helps remember the factors affecting suction lift?
CRESTA
43
What does 'C' in CRESTA stand for?
Creation of flow: A proportion of atmospheric pressure is used to create water flow.
44
What does 'R' in CRESTA represent?
Resistance to friction: Friction loss in the suction hose is determined by hose length, interior surface, diameter, and water speed.
45
What is meant by 'Entry loss' in the context of suction lift?
Entry loss is caused by changes in direction as the water enters the pump impeller.
46
How does the size of the suction hose affect flow?
The larger the diameter of the suction hose, the greater the flow.
47
What happens to water temperature inside the suction hose?
At lower pressures, water boils and vaporizes at lower temperatures, which can break the water column and cause the pump to lose its prime.
48
What is atmospheric pressure's role in suction lift?
Atmospheric pressure is the only pressure available to force water up a suction hose.
49
What is the difference between positive and negative pressure?
Positive pressure is above atmospheric pressure (100 kPa), while negative pressure is below atmospheric pressure.
50
What does negative pressure correspond to when using a static water supply?
Negative pressure on the inlet side of the pump usually corresponds to the lift being achieved.
51
How does negative pressure relate to lift?
For example, a pressure of -30 kPa corresponds to a lift of 3 m because 1 m of head is equal to 10 kPa of pressure.
52
What causes friction loss in hydraulics?
Friction loss is caused by factors such as the Length of hose, Internal surface, Diameter of hose, and Speed of water (LIDS).
53
How does friction loss affect pressure?
The greater the friction, the greater the loss of pressure. More pressure must be applied to overcome friction.
54
What is the safe maximum working pressure of a hose?
The safe maximum working pressure of a hose is 1050 KPa.
55
How does friction loss vary with hose diameter?
Friction loss decreases with an increase in diameter for the same velocity.
56
What factors influence friction loss?
Friction loss varies with the length of the hose, increases with the roughness of the inside of the hose, increases as the square of the velocity, and is independent of pressure.
57
How does flow rate affect friction loss?
The higher the flow rate, the greater the pressure loss from friction. ## Footnote Low flow rate over a 25 m length = 15 kPa friction loss; High flow rate over a 25 m length = 50 kPa friction loss.
58
What is the relationship between flow rate and friction loss?
Double the flow rate results in four times the friction loss; half the flow rate results in one quarter of the friction loss.
59
How does running hoses in parallel affect friction loss?
For the same flow, friction loss decreases when two hoses are run in parallel.
60
Can flow rate always be adjusted to reduce friction loss?
No, some equipment, such as large nozzles and ground monitors, require a high flow rate.
61
What is velocity in the context of water flow?
Velocity is the speed and direction at which water is flowing through a nozzle, hose or a pipe.
62
How do you calculate velocity?
To work out velocity, take the volume flow in cubic metres per second and divide it by the area. This gives the velocity in m/sec.
63
How do you calculate the volume of a rectangular swimming pool or tank?
Volume (in litres) = length x width x depth x 1000
64
What should you do if the depth of the tank or pool is uneven?
Calculate the average depth by checking the depth in different parts, adding these together, and dividing by the number of measurements.
65
How do you find the average depth for a swimming pool that is shallower at one end?
Take the depth at each end and divide by two.
66
How do you calculate the volume of a round water tank?
Volume (in litres) = 0.8 x diameter² x depth x 1000
67
How do you find the diameter of a round tank using paces?
D = Circumference (paces round tank in metres) / 3

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