Pumping Operations Flashcards
What is a pump
A pump is a machine, driven by some external power, for transmitting energy to fluid. Could be hand pump or suitable driven engine.
What is a centrifugal pump
A centrifugal pump operates by using centrifugal force, that is, the tendency of a revolving body to fly outward from the centre of rotation.
The construction of the centrifugal pump consists of two main parts:
Impeller
Casing
The centrifugal pump converts kinetic energy into pressure energy.
What is the impeller
The impeller is rotated by means of an external power source.
Rotation induces a flow of water through the impeller passages and causes a partial vacuum at its inlet, which in turn induces more water into the suction inlet.
Water from the suction inlet (eye) is picked up by the impeller vanes and is energised as the impeller spins then discharged at high velocity out the periphery. As the water enters the casing most of this kinetic energy is converted into pressure energy.
What is the casing
The casing is designed to reduce turbulence and friction by creating as smooth a flow as possible.
The kinetic energy of the water when it leaves the impeller is converted into pressure energy as the water enters the casing. This is achieved by reducing the velocity of the water.
What is the volute
Shaped like a snail shell.
Water is thrown from the impeller and travels through a passage that steadily increases in cross sectional area until the delivery outlet.
This reduces the velocity of the water.
What are impeller vanes
Water enters through the inlet and travels towards the periphery through the vanes by centrifugal force. As it travels through the vanes it increases speed and discharges as high velocity.
How does a centrifugal pump work
Water is drawn from the suction inlet.
Water flows through the impeller vanes driven by external source making a partial vacuum and increasing velocity and kinetic energy.
Water enters the casing and travels through the volute reducing velocity and transferring kinetic energy into pressure energy.
High pressure pump
Is separate to main pump.
Must be activated in cabin first.
Should operate at 2000 kPa to produce significant atomisation.
Designed to operate to 4200 kPa where the kunkel valve will relieve pressure above.
HP casing only hold 1L of water and must be cooled if on but not in use.
How is the pump shaft sealed
By mechanical seal
Scania Urban Pumpers Capacity
Darley LMDH 1000 main pumps rated capacity of 3800 L/min at a pressure of 1000 kPa.
Darley LMDH 1500 main pumps rated capacity of 5700 L/min at a pressure of 1000 kPa.
Darley LMDH 1000 high pressure pumps rated capacity of 380 L/min at a pressure of 4100 kPa.
Fire ground calculations
Pressure and head calculations
Pressure is the force at which water is delivered.
Head is the vertical depth of a water column.
P = H x 10
In kPa
What is cavitation
When boiling occurs in the suction side of the pump.
This occurs when the pressure on the suction side of the pump falls below the vapour pressure of water.
Can cause major damage to impeller.
Causes of cavitation
The lift is too high for the volume of water and pressure being discharged.
The suction hose diameter is too small for the volume of water being discharged.
There may be a restriction or partial collapse of the suction line.
Hydrant supply being over-run.
Indicators of cavitation
The pump will make noise like there were many small stones passing through. (this is imploding vapour bubbles)
The engine evolutions will increase. (the engine is not pushing as much water so the engine does not have to work as hard)
When operating from a hydrant supply, the compound gauge will show a negative pressure and the collector hose will go soft. (over running supply)
When droughting, the compound gauge will show the maximum lift (will drop below -75kPa)
Decrease in delivery flow.
Air in the pump
Will produce some of the same sign as cavitation but is not cavitation and will not damage the pump as it goes through at the same pressure as the water.
Purpose of flow gauges
To measure the amount of water flow through a pipe.
Operate via internal paddle wheel sensor.
Points to remember for throttle control
Always return to idle position at the completion of pump operations.
Use in conjunction with opening and closing deliveries and outlets to maintain correct kPa.
What will the emergency shutdown button do and how can you reset it
Emergency shutdown will stop engine and pressure to all deliveries will be lost. To reset: Reset emergency stop button. Return throttle to idle. Select neutral. Disengage pump and HP hose. Turn ignition off and wait 10 seconds, Restart engine. Engage pumps. Select 'D' on auto transmission. Re-commence pumping.
How to control gated valves
Should be operated in a smooth manner to avoid water hammer when opening and closing.
Watch pressure and adjust throttle to maintain correct kPa.
Can be slightly closed to keep pressure but limit volume, if tank is running out too fast.
When are drain valves used
Delivery drain valves are used to release the pressure from a charged line of hose when it cannot be done via the branch.
Pump drain valves are used to completely empty the main pump casing. (mainly for workshops)
Purpose of pump pressure gauge
Indicates the delivery pressure of water from the main pump to the 64mm deliveries and monitor. Of bourdon tube design.
Purpose of high pressure gauge
Indicated the delivery pressure of water from the high pressure pump to the 25mm high pressure hose reels.