Pressure Loss Calculations

Question 1

The 2 main reasons for the reduction in pressure?

Answer 1

Frictional loss in hose.

Effects of gravity when working above water supply

Question 2

The smaller the internal diameter of the hose, the greater the amount of frictional loss

Answer 2

.

Question 3

The higher the required output flow m, the higher the amount of frictional loss

Answer 3

.

Question 4

Will working below the supply of water mean pressure gain?

Answer 4

Yes

Question 5

Will a longer hose, or a hose with more length fitted experience a greater pressure loss?

Answer 5

Yes

Question 6

If a flow rate through a hose is doubled, how much pressure will be lost due to friction?

Answer 6

Increased by a factor of 4

Question 7

3 laws of frictional loss?

Answer 7

The longer the hose, the greater the friction loss.

If the hose is doubled, the frictional loss will increase by a factor of 4

The smaller the internal diameter, the higher the frictional loss. (45mm hose is approx 5 times greater than 70mm and 32 times greater than 90mm hose)

Question 8

Does pressure loss due to friction increase as flow rate increases?

Answer 8

Yes,

But it doesn’t for pressure

Question 9

How much frictional loss is experienced in one length, (23m) of 45mm hose with a branch at 400lpm?

Answer 9

1 bar per length of hose.

Question 10

How much pressure is lost due to frictional force in 1 length (23m) of 70mm hose.

Answer 10

0.2 bar per length.

Question 11

What are the effects of gravity when working above or below the supply of water?

Answer 11

-1 bar per 10m of height above (0.1bar per 1meter)

+1 bar per 10m below the water supply (0.1 bar per 0.1 meters)

Question 12

What should you do if an overall pressure loss is less than 0.5 bar?

Answer 12

Ignore it.

Question 13

What should you do if a pressure loss is between 0.5 and 1 bar?

Answer 13

Round it up.

Question 14

When using a delta branch, adding 1 bar per 45mm hose, and 0.2 bar per 70mm of hose will make sure a efficient pressure at the branch is achieved regardless of flow setting at branch.

Answer 14

.

Question 15

Most floors are 3 meters in height, meaning a pressure loss of?

Answer 15

0.3 bar per floor.

Question 16

Who is responsible for making pressure loss calculations and adjustments to the ‘water on’ order?

Answer 16

The branch operator

Question 17

What should the pump operator do if required pressures cannot be met?

Answer 17

Inform incident commander.

Question 18

What diameter of hose should be used when you augment the water supply?

Answer 18

The largest possible.

Water supply should be twinned from hydrant

The amount of pressure lost due to friction is quartered when twinned

Question 19

What does using a 45mm hose at branch length archive?

Answer 19

Branch operator has more manoeuvreabilty whilst allowing the pump to work more efficiently at lower engine speed

Question 20

What is the most important single factor which effects frictional loss?

Answer 20

Diameter of hose

Question 21

How much pressure loss due to frictional corse will be occur, when a 70mm hose is supplying a pump from the hydrant at 2000lpm?

Answer 21

2.7 bar

Question 22

4 factors effecting pressure loss?

Answer 22

Internal diameter

Output of flow

Height in meters above or below supply

Length of hose line

Question 23

What is ‘the head of water’?

Answer 23

A column of water exerting a downward pressure.

1 bar for every 10m

0.1 bar for every meter

Question 24

How much pressure loss due to friction does a 45mm hose have on the different flow settings?

Answer 24

130lpm - 0.3bar

230lpm - 0.3 bar

300lpm - 1 bar

400lpm - 1 bar

PER LENGTH 23meters

Friction loss on 70mm hose is negligible on these flow settings due to larger diameteru

Question 25

For foreground pressure loss calculations, any pressure under 0.5 can be ignored, and pressure loss over 0.5 should be rounded up.

Answer 25

.

Question 26

Can 45mm hose be used to augment a supply?

Answer 26

NO

Question 27

The lower the branch pressure, the shorter the throw before jet is broken up.

Answer 27

.

Question 28

Practical considerations?

Answer 28

1 bar per length of 45mm of hose, regardless of flow.

45mm losses 1 bar at 300 and 400 lpm, and 0.3 bar at 130 and 230 lpm

70mm hose losses 0.2 bar per length regardless of flow rate

<0.5 ignored, >0.5 rounded up

70mm and 90mm suffer less frictional loss

3meters per floor. (0.3 bar)

Twinned hose lines, pressure lost due to friction is quartered

Lower the branch pressure, shorter the throw

Always consider using 70mm delivery hose, to 45mm branch length

Reducing flow rate at beach will reduced frictional loss. (If safe to do so)

Branch operater responsible for calculating pressure loss and adjusting water on order.

Pump operater responsible for supplying correct pressure, and if it cannot be achieved informing crew, and incident commander.