Pumps And Primers Flashcards
What is the definition of a pump?
A pump is a machine driven by some external power, used for transmitting energy to fluids
All pumps fall into three categories, what are they?
Positive displacement
Ejector or jet
Centrifugal
Centrifugal pumps are comprised of two main parts. What are they?
Impeller
Casing
3 gauges - high pressure, low pressure & compound are found on the rear of the appliance. What are they for?
High pressure gauge - displays output of hose reel jets
Low pressure gauge - displays output of main jets
Compound gauge - displays positive pressure of incoming supply, and negative pressure of over drawing the supply.
What are the characteristics of centrifugal pumps?
- At any given speed where there is no flow, (no delivery open) the pressure is at a maximum
- pressure decreases with an increase in discharge (opening of a delivery)
- pressure and flow increase as the pump speed is increased and vice versa
- when suction lift is increased pressure and flow decrease
When working from a pressure fed supply (hydrant) what could cause the supply to fail?
Failure of the supply itself (fractured main or a burst hose between the hydrant and the pump)
Over running the supply
What could be the cause of increased delivery pressure whilst at work? (This should be investigated at once as it implies a stoppage of some sort on the delivery side)
Kinks in the delivery hose
Vehicles standing on or debris fallen onto delivery hose
Blockage of jets by small stones which have passed through the pump
(Closing of the branch will also cause increased delivery pressure and gauges should be closely monitored to ensure other branches do not receive increased pressure)
What could cause a decrease in delivery pressure whilst at work?
Delivery hose burst
Branches being opening up
Pumps can be filled with water (known as priming) by three methods, what are they?
Elevated supply (water forced in by gravity, air pushes out) Pressure supply (water forced in by hydrant, air forces out. Known as soft suction) Use of a primer (only used when working for open water. Air pumped out. Atmospheric pressure forces water up into the pump.
What are the 3 types of primer?
Reciprocating (not used in modern appliances)
Exhaust gas ejector (used to prime portable pumps)
Rotary water ring (used on modern appliances to prime the centrifugal pump)
When working from open water, the pump fails to prime and you have a no vacuum reading. What could’ve caused this?
Strainer not adequately submerged Loose or faulty suction joints A delivery valve not properly seated or closed Air leaks in the suction hose Defective primer Air leak in the pipes to gauges Clapper valve on an exhaust ejector primer not seating Lack of water in the water ring primer.
When working from open water, the pump fails to prime and you have a high vacuum reading. What could’ve caused this?
Blockage of the basket or metal strainer
Faulty suction hose (the inner walls have separated and collapsed)
When working from open water, and whilst at work, you get decreased vacuum reading. What could this mean?
Level of static supply has risen
Less water being used by the branch (branch has been closed)
Working from open water and whilst at work, you get an increased vacuum reading. What could this mean?
Drop in the level of the static supply
More water being delivered (branch opened)
Blocked suction strainer
What is C in creft and what does it mean?
Creating the flow - a proportion of the atmospheric pressure is taken up in creating the flow
What is R creft and what does it mean?
Raising the water - from its existing level to the pump outlet
What is E in creft and what does it mean?
Entry loss - overcoming resistance due to the changes in direction as the water enters the pump impeller
What is F in creft, and what does it mean?
Frictional Resistance - to the water on both entering and passing through strainers and hose
What is T in creft and what does it mean?
Temperature of the water - the warmer the water the less lift can be attained as it tends to vaporise in the hose causing the pump to become unprimed.
When working from open water what is the term used to describe the distance the water must travel from its source to the the inlet of the pump?
Lift
What are the theoretical and expected lift distances?
Theoretical - 10m
Expected - 8m
What are the duties of a pump operator?
Control of the discharge pressure carefully and make any changes gradually
Ensure water supply is maintained constantly
If it is necessary to cut off the water supply due to various reasons, every effort must be made to warn branch operators before this happens
Watch gauges constantly whilst pump operating. They will they will tell you what is happening with regards to supply of and delivery
Ensure the tank supply is full at all times so it is ready for use if necessary
Ensure that, as pump operator, you know exactly where all your deliveries are working
What pressure should hose & main jets be?
Hose reel - 25 bar (high)
Main jet - 3/8 (low)
3 bar pressure if branch operator hasn’t given the bar
Changes 1 bar at a time
What are the advantage of ejector pumps
No moving parts parts
They will in oxygen deficient atmospheres
Little attention is required while operating
Who is responsible for calculating pressure required at the pump?
Branch operator
Where is the HPVU based?
Sheldon
Advantages of a centrifugal pump
Simple maintenance
They are small, light and compact relative to output
Can be run against closed deliveries without damage or danger
Can be driven directly from an internal combustion engine
