Chapter 9 Flashcards
Positive displacement pumps are?
Self priming, deliever a definite volume of water or air. And exhaust air from the pump and deliver water
Positive discharge pumps are called “constant flow machines” because?
They produce the same flow at a given speed regardless of discharge pressure. All the air and water are forced out of the pump with each operating cycle
What type of pump are modern fire apparatus equipped with as their main pump?
Centrifugal pump
How do centrifugal pumps create pressure needed to achieve proper drainage charge pressure?
Depends on the velocity of the water produced by the centrifugal force to provide the pressure
What are positive displacement pumps used for in modern apparatus?
They are used as priming devices to get water into the centrifugal pump during drafting operations
Piston pumps can provide pressures up to what psi 1000 psi?
Piston pumps?
What type of pump from the standpoint of design is the simplest type of pump?
Rotary pumps
What are rotary pumps used for in modern apparatus?
Confined to small capacity booster type pumps low volume high pressure pumps and priming pumps
How do rotary gear pumps work?
Consist of two gears that rotate in a tightly meshed pattern inside a watertight case. They are constructed to contact each other and are in close proximity to the case. This allows it to force air or water out of the pump with each gear creating airtight or watertight pockets
Rotary gear is what type of pump because each pocket in the gears contains a definite amount of water which is forced out of the pump each time the gears turn with a positive action
Positive displacement pump
What are most gear pumps gears are made of ___ and pump casing is made of?
Bronze or another soft metal for the gears, and a strong alloy such as cast metal for the pump casing
Rotary vane pumps are constructed by?
Moveable elements that automatically compensate for wear maintenaning a tighter fit with closer clearances as the pump is used.
What is one of the most common types of pumps used to prime a centrifugal fire pump?
Rotary vane pump
What feature makes the rotary vane pump much more efficient than the rotary gear pump at pumping air?
The self adjusting feature. When the vane that is in contact with the casing becomes worn, centrifugal force causes it to extend further causing it to maintain a tight fit
What is a centrifugal pump classified as?
Non displacement pump as it does not pump a definite amount of water with each revolution
The volume capacity of the pump is dictated by?
The size of the impeller
The increase in pressure is roughly equal to the square of the change in the?
Impeller speed. Double the impeller speed, will result in 4 times as much pressure
Is a centrifugal pump able to pump pump air and be self priming?
No, it is not able to do do either
What are the two basic types of centrifugal pumps used in the fire service?
Single stage and multi stage.
A double suction impeller is used to?
Minimize lateral thrust of large quantities of water entering the eye of the impeller. The double suction takes water in from both sides the reaction being equal and opposite cancels out the lateral thrust
Why is radial thrust cancelled out in double suction impellers?
Water is removed at two places and traveling in opposite directions.
This part helps create a hydraulically balanced pump that reduces stress on the pump, vehicle chassis, and helps lengthen the service life of the pump and apparatus.
Double suction impeller
What feature makes multi stage pumps more efficient?
The capability to connect the stages in series for maximum pressure, or in parallel for maximum volume by use of a transfer valve
Series means?
Maximum pressure
Parallel means ?
Maximum volume
The process between switching over from pressure and volume is known as?
Changeover
What should be done if making any changeover on the fireground?
Carefully coordinate with attack crews so that they will be prepared for a slight interruption during the transfer
If there is any question as to the correct position for the transfer valence it is best to operate in?
Parallel(volume) rather than series(pressure)
What is good to remember as far as your limitations for series(pressure) mode?
The volume of water available while operating in the pressure position is limited to the amount that one impeller can supply
How can you check the operation of a clapper valve?
Checked by removing the strainer from a large intake opening and reaching into the pump with a long wooden dowel or similar type of rod. The flapper valve must be able to swing freely
A very close tolerance must be maintained between the pump casing and the hub of the impeller. This opening is usually limited to?
.01 inch any increase in the opening lessens the effectiveness of the pump
What is an initial indication of wear on a pump?
During pump test when increased engine rpm is required to pump at the rated capacity