Describe a Centrifugal Pump?
A centrifugal pump operates by using centrifugal force
tendency for a revolving body to draw outwards from the centre.
This converts kinetic energy into water pressure energy.
Impeller and a casing.
Label the 5 parts of a single stage pump
- Delivery outlet
- Impeller
- Volute
- Guide vanes
- Water Inlet (eye)
Describe the Volute
A snail shaped casing that slows the velocity of water coming from the impeller.
Describe the Eye
The water inlet of the impeller. Centrifugal force creates a low pressure area where water is sucked into the impeller.
What is the impeller?
The impeller rotates to create centrifugal force which sends water outwards from the centre.
Describe the casing
The casing is an airtight passage surrounding the impeller.
Reduces turbulence and friction by creating as smooth a flow as possible, reduces the velocity of the water.
What are the guide vanes?
They guide water from the eye to the volute smoothly to reduce turbulence and increase efficiency.
What are the pump capacities for
LDMH-1000 at 1000kpa and LDMH-1500 at 1000kpa?
3,800 lpm and 5,700 lpm
What volume of water is used to cool our Darley pumps?
18lpm (new pumpers have 60 lpm)
What happens if the pump operates without any discharge?
Pressure energy is converted to heat energy and if allowed to build up the pump can be damaged.
Formula for the relationship between pressure and head?
Pressure= Head x 10
P= Hx10
Describe cavitation
When in a vacuum, water will boil at a lower temperature. This causes vapour bubbles which then implode, leading to damage to the impeller.
List causes of Cavitation
- Delivery of water is more than collection of water
- Hydrant is being overrun
- Draughting hose or collection line diameter is too small or is being restricted
- The lift is too high for the volume of water and pressure being discharged
List indicators of Cavitation
- Sounds like small stones passing through the pump (this is the implosion of the vapour bubbles)
- Compound gauge will drop into negative
- Decrease in pressure for deliveries
- Collector hose will go soft (when working from a hydrant supply)
What happens when the emergency shut down button is pressed?
Shuts down the engine, and all pressure to all deliveries is lost.
What the restart procedure after the emergency button has been pressed?
Idle
Turn ignition OFF
Turn ignition ON (restart engine)
The pump switches are still engaged
Select ‘D’ Drive
Pumping can recommence
What is the pressure when using a hydrant?
800kpa
What are the 4 types of gages on the pump panel and what do they show?
- Compound Gage- shows the pressure at which the water is entering the pump. Shows the relationship between water in and out
Indicates lift when draughting - Main Pressure- Reads and displays the pressure of water delivery from main pump in KPA
- High Pressure pump- shows the pressure of the delivery from the HP Pump/hose
- Flow gages- shows each delivery’s litres per minute
What are 4 supplementary cooling techniques?
- Run either of the HP hose on a ‘flush’ stream near front tyre
- Run the HP hose into the inspection hatch on roof of pumper.
- Regularly open branches
- Pump water from delivery to tank filler storz which creates a closed circuit
- Throttle back so pump is running at a lower RPM to prevent overheating
What KPA do we run the HP hose at?
2000 kpa
What seals are used in ACTFR pumps?
Mechanical. Ceramic faced. Primary ring (static) Mating ring (rotates). These seals will be damaged if subjected to prolonged dry running
When using the appliance-based monitor, we must only turn it on when?
When pump is at idle (under no pressure). Always tie it off.
Water tank capacity of 1500L, The crew is using 2 HP hoses working at 2000kpa, How much time do you have to get water into the pump?
Lpm = KPA/10-50
2000kpa / 10 - 50
200-50
= 150 x 2 (the two HP hoses)
= 300
Time = Capacity / lpm
1500L / 300
= 5 Minutes
You’re supplying water to the 25th floor, the Branch man requires 800kpa, what pressure to you need to supply at the truck to achieve this?
30 kpa per floor
=25x30
=750
Therefore 800kpa (hydrant pressure) +750
=1550kpa
