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									Service Delivery 3

    Hydraulics
            Aim

To ensure students can explain
the principles of obtaining and
delivering water.
           Learning Outcomes
  At the end of the session students will be
  able to:
• Understand the relationship between atmospheric
  pressure and suction lift
• Describe the principal characteristics of pressure
• Describe how friction causes pressure loss
• Explain the term ‘jet reaction’
• Carry out basic fireground calculations.
        Calculating areas.
    w                                   w

Area = wXh
                   h        h      Area =
                                vertical hXw


                   a
             Area = a+bXh
                    2

                   b
Calculating volumes.

     r



h




                        2
          Volume =   r  h
    Calculating volumes.

     d




h



         w       Volume = hXwXd
Calculating volumes.



   Water




           Volume = 2 x a x d
                        3
Pressure is perpendicular to any
    surface on which it acts.

           Atmospheric
             Pressure
Pressure at any point in a fluid at rest is
of the same intensity in all directions.
                   Pressure
                   Gauges
Pressure applied from outside to a
fluid contained in a vessel is
transmitted equally in all directions.
 Pressure gauges   Pressure   Pressure gauges
     Downward pressure of a fluid in an
     open vessel is proportional to depth.




                              3m

                2m


1m
The downward pressure of a fluid in
an open vessel is proportional to the
density of the fluid.




                       Water
                       136mm
Mercury
10mm
The downward pressure of a fluid on
the bottom of a vessel is independent
of the shape of the vessel.
Lifting water by atmospheric pressure.
                         vacuum




  Atmospheric pressure
     approx 1bar



                          Water
        Theoretical lift

Approximately 10 metres - assuming a
perfect vacuum can be created and the
water is cool and pure.
        Pressure and head
• The height to which water is lifted or
  pumped is referred to as the head

• To raise a column of water 1 metre in
  height requires a pressure of 0.1bar.
  This applies to both ‘suction head’ and
  ‘delivery head’.
Factors limiting suction lift
• Lifting water from it’s existing level to
  the pump inlet
• Overcoming frictional resistance to
  the water
• Turbulence at the pump eye
• Creation of flow.
        Practical lift

Because of these factors the
maximum practical suction lift is
generally regarded as 8 metres.
Lifting practically.



      7m               2m

      3m               8m




    water
   water
                   water
Five principal laws govern the
loss of pressure due to friction.
Friction loss varies directly with the
length of the hose

            Friction loss      0.4b

                0.2b




                1                2
            Hose lengths .
For the same velocity friction loss
decreases with the increase in diameter




  45mm        70mm           90mm.
  Friction loss increases directly with
  the square of the velocity


2000 litres/min    pressure loss   6bar



1000 litres/min    pressure loss 1.5bar.
Friction loss increases with the
interior roughness of the pipe.
For all practical purposes, friction
loss is independent of pressure.
   Calculating jet pressures
 Pressure loss due to friction;

• 70mm non-percolating hose 0.2 bars
  per 25 metre length.
Pressure loss due to head

             For every metre in
             height that water is
             pumped 0.1bar of
             pressure is lossed.
            Question
6 lengths of hose are being used to supply
a branch deployed at a height of 15m

What pressure will be required at the
pump to supply 3 bars pressure at the
branch.
                  Answer
Nozzle pressure required                6 bars
Pressure loss due to head 0.1b X 15 = 1.5b
Pressure loss due to friction 0.2b X 6 = 1.2b

Pump pressure required                8.7bars
Fireground flow rate calculation


• 45mm diameter hose = 300 litres/min

• 70mm diameter hose = 600 litres/min
Function of a branch and nozzle


 To convert pressure energy into
 velocity energy and ensure that an
 effective jet of water leaves the
 nozzle.
Achieved by reducing the cross-sectional
area that the water is flowing through




     45mm
     diameter
     hoseline
                            20mm diameter
                            nozzle.
  Advantages of higher nozzle
  pressures
• A greater striking power is achieved

• A longer reach can be obtained

• A larger volume of water is applied.
     Factors affecting the
     pressures adopted
• The type and size of nozzle used

• The type of jet required

• The intensity of the wind.
            Jet Reaction
The magnitude of the reaction is
dependant on;

• The mass of water per second passing
  through the nozzle

• The squared diameter of the nozzle.
Jet Reaction
Jet Reaction

                 2
= 1.57 x p x d
       10
                 2
  1.57 x p x d
       10

Using a 25mm nozzle at 7 bars pressure

            R = 1.57× 7 × (25x25)
                    10

             = 687 Newtons.
                 2
  1.57 x p x d
       10

Using a 12.5mm nozzle at 7 bars pressure

            R = 1.57× 7 × (12.5x12.5)
                    10

             = 172 Newtons.
              Confirmation
  Assessments will be based on this lesson and
  the corresponding study note
             Learning Outcomes
• Understand the relationship between
  atmospheric pressure and suction lift
• Describe the principal characteristics of pressure
• Describe how friction causes pressure loss
• Explain the term ‘jet reaction’
• Carry out basic fireground calculations.
THE END

								
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