Fire Service Pumps

Question 1

Requirements of a Fire Service Pump

Answer 1

• Self contained
• Able to handle large quantities of water
• Able to produce fairly high pressures
• Reliable
• Easy to operate and maintain
• Able to pump against a closed delivery

Question 2

Types of Pumps

Answer 2

Positive displacement pumps; those that can displace liquids and gases.

Non-Positive displacement pumps; those that can displace liquids only (a primer is required to pump air from the system

Question 3

Advantages of Centrifugal pumps

Answer 3

• Simple maintenance
• Can be run against closed deliveries without damage
• Light and compact relative to their output
• Can be driven directly from an internal combustion engine.

Question 4

Non-Positive Displacement Pumps

Centrifugal

Answer 4

• At any given speed where there is no flow, pressure is at a maximum
• Pressure decreases as the deliveries are opened and flow increases
• When the pump speed increases, pressure and flow increase

Question 5

Impeller

Answer 5

• Water is drawn into the eye
• Shaft
• Rotating impeller
• Water is thrown off the impeller due to centrifugal force
• Volute
• Water is discharged from the volute

Question 6

Non-Positive Displacement Pumps

Peripheral Pump

Answer 6

• Delivers high pressure
• Ring of guide vanes
• Prevents wear and tear to centrifugal pump.

Question 7

Low Pressure Guage

Answer 7

• Indicates the pressure in ‘bars’ of the water in the pump and entering hose lines
• It does not record the pressure at the branch unless the branch is closed down.

Question 8

High Pressure Guage

Answer 8

• Indicates the pressure in ‘bars’ of the water in the pump & entering the high pressure hosereels
• It does not record the pressure at the branch unless it is closed down.

Question 9

Compound Guage

Answer 9

Records a negative pressure when working from an open source and a positive pressure when working from a pressure fed supply

Question 10

Working from a Pressure Fed Supply

Failure of water may be caused by:

Answer 10

• Failure of the mains supply, such as a fractured main or burst delivery length of hose
• Choked internal strainer in pump
• Over-running the supply causing the soft suction to flatten.

Question 11

Working from a Pressure Fed Supply

Increased delivery pressure may be caused by:

Answer 11

• Hand controlled branches being shut down
• Sharp kinks in delivery hose
• Vehicles parked or collapsed debris on delivery hose
• Surge in mains pressure
• Blockage of nozzle by stones when internal strainer omitted.

Question 12

Working from a Pressure Fed Supply

Decreased delivery pressure may be caused by:

Answer 12

• Hand controlled branches being opened
• Burst length of delivery hose
• Drop in mains pressure.

Question 13

Cavitation

Answer 13

• Bubbles form because of pockets of low pressure occurring around the centre of the impeller and this causes the water to vaporise
• Trying to supply more water than is coming in to the pump – the remedy is to ease off the throttle
• This is exaggerated when the water is hot.

Question 14

Frictional Loss

Answer 14

● Friction loss varies directly with the length of the hose
● For the same velocity, friction loss decreases with the increase in diameter
● Friction loss increases with the interior roughness of the hose
● Friction loss is independent of pressure.

Question 15

Frictional Loss / Calculating Pump Pressures

Answer 15

Pressure loss due to friction:
70mm hose, 25m length 0.2 bar
45mm hose, 25m length 0.4 bar
For every metre in height 0.1 bar

For example:
40m @ 0.1 bar per metre = 4 bar pressure loss.