Chapter # 10 Fire Pump Theory Flashcards
Are the majority of water systems unable to maintain adequate pressure in the hydrant system for effective fire fighting.
Yes, that is why we need fire pumps.
What was the earliest type of pump used in the fire services?
Hand operated piston pumps.
A positive action takes place. All water and air are forced out of the pump body with each operating cycle.
Positive displacement pumps
Do modern apparatus have a positive displacement pump?
Yes, this allows drafting.
Does not use positive action; rather it depends on the velocity of water produced by centrifugal force to provide the necessary pressure.
Centrifugal pump
What are two types of positive displacement pumps?
Piston and Rotary
The forward stroke causes water (or air) to be discharged, and the return stroke causes the pump to fill with water (or air) again. This is known as what?
Single action piston pump.
Adding additional valves to piston pumps can produce a usable fire stream. This is known as what?
Double acting piston pump. Because it both receives and discharges water on each stroke of the piton. (up and down).
What is the output capacity of a piston pump determined by?
The size of the cylinder and the speed of the piston travel.
It is more practical to build……….. pumps than one large single cylinder pump.
muticylinder
What can help to minimize the pulsing of a piston pump fire stream?
A air chamber.
Name some reasons the piston pump has been faced out as a high capacity fire pump.
Pulsating stream. Prone to wear. Can not pump dirty water (unless bronze).
Although piston pumps are no longer used as high capacity fire pumps, are they still used to provide high pressure fire streams? In what applications?
Yes, Muticylinder, PTO driven pumps provide pressure up to 1,000 psi. for high pressure fog lines or to inject foam concentrate into a water line or manifold at a higher pressure then what the water pump is creating. All provide a dependable relief valve.
The simplest of all fire pumps from the standpipe of design.
Rotary pumps.
Used in the past as the main fire pump. Used today as small capacity booster type pumps, low volume high pressure, and priming pumps.
Rotary pumps
Name two types of rotary pumps.
Rotary vane or Rotary gear.
Has two gears that rotate in a tightly meshed pattern inside a water tight case. Rotate from the intake to the discharge. Creates pockets of water or air when the tooth’s come in contact with each other.
Rotary Gear Pump
What determines the amount of water that a rotary gear pump can produce?
The size of the pockets in the gears and the speed of rotation.
Are rotary gear pumps prone to damage? Can they pump dirty water.
Yes, Can wear very easily from pumping dirty water.
Constructed with movable elements that automatically compensate for wear and maintain a tighter fir as the pump is used. One of the most common types of priming pumps on apparatus. Rotor is mounted off center in a housing. As the rotor turns the vanes move against the casing. The intake side of the casing is larger then the discharge side of the casing.The self adjusting feature make it much more efficient in pumping air then a standard rotary gear pump.
Rotary Vane Pump.
How are Rotary Pumps powered?
Either a small electronic motor or through a clutch that extends off the apparatus drive shaft.
A nonpositive displacement pump because it does not pump a definite amount of water with each revolution. Rather, it imparts velocity to the water and converts it to pressure within the pump itself.
Centrifugal pump
What are the two parts of a centrifugal pump?
Impeller and Casing.
Transmits energy in the form of velocity to the water.
Impeller
Collects the water and confines it in order to convert the velocity to pressure. Then directs the water to the discharge of the pump.
Casing
What rpm does the impeller generally rotate at?
2,000 to 4,000 rpm.
To some extend the volume capacity of a pump is dependent on what?
Th size of he eye of the impeller. The larger the eye the greater the flow capacity.
Why is the impeller mounted off center in the casing?
Creates a water passage that gradually increases in cross-sectional are as it nears the discharge outlet of the pump. This section of the pump is called the Volute.
What are the three main factors that influence a centrifugal fire pumps discharge pressure?
Amount of water being discharged. Speed at which the impeller is turning. Pressure of water when it enters the pump from a pressurized source.
T or F In a centrifugal fire pump, the greater the volume of water being flowed, the lower the discharge pressure.
True
T or F In a centrifugal fire pump, the greater the speed of the impeller, the greater the pressure developed.
True. This increase is approx equal to the square of the change in impeller speed.
Doubling the speed of the impeller results in what?
Four times as much pressure if all other factors remain constant.
Because the incoming pressure adds directly to the pressure being developed by a centrifugal pump, incoming pressure changes are reflected where?
In the discharge pressure.
Name the two basic types of centrifugal pumps.
Single stage and Two stage.
What is a double suction impeller.
A impeller that take water in from both sides. This was done to cancel out the reaction of only having water enter from one side. With it entering on both sides the reaction has no effect. It also provides a larger water way for the movement of water. Provides a hydraulically balanced pump. Used in high capacity pumps with large impellers.
What is series? What is parallel?
Both are stages of a muti-stage fire pump. Series = Pressure, Parallel = Volume
What is the capacity of a pump in parallel (volume) position?
Each impeller is capable of delivering its rated pressure while flowing 50% of the rated capacity; therefore, the total amount of water the pump can deliver is equal to the sum of each of the stages.
Front mount pumps, power take off, separate engine driven, and midship transfer pumps use a single intake impeller and a simple casing to provide capacities up to how many gpm?
2,000 gpm
When pumping in series (pressure), what is the increase in pressure that is provided by the first impeller before moving to the second impeller?
50%-70%.
What is the total volume of water limited to when pumping in series (pressure)?
What one impeller can provide.
The process of switching between volume and pressure?
Changeover
When do most manufacturers today recommend that a pump be switched to volume?
When it is necessary to flow more than 2/3 of the rated volume capacity.
In most cases, what is the maximum net pump discharge pressure that a transfer valve should be operated at?
50 psi
Can provide 100% of the rated volume at 150 psi.
Parallel (Volume)
How is the transfer valve operated on many two stage fire pumps?
Manually. Especially on older apparatus.
How might a transfer valve be operated on a newer apparatus?
With a power operated transfer valve.
How can a power operated transfer valve be powered?
Electricity, Air pressure, Vacuum from the engine intake manifold (gas engine only), water pressure.
T or F Many power operated transfer valves operate at pressures as high as 200 psi.
True
What has been done in the past to gain higher pressures?
A series of four impellers to develop pressure as high as 1,000 psi. A single stage pump that takes from a multistage pump, when pressures higher then 250 psi are needed.
The pressure in the volute is much higher then it is in the eye of the impeller, so a very close tolerance must be maintained between the pump casing and the hub of the impeller. This opening is usually limited to what? Any increase in the opening lessens the pumps effectiveness.
.01 inch or less.
What is the first indication of wear to a centrifugal pump?
When increase engine rpm is required to pump the rated capacity in pump test.
What are some newer apparatus centrifugal pumps equipped with to prevent damage due to the build up of heat?
Thermal relief valve (sends water to tank or atmosphere).
If a driver places their hand on the direct pump intake pipe and it is warm, what should be done?
Open a discharge or a circulator valve.
What is used to maintain a semi tight seal at the point where the gear shaft passes through the pump casing?
Packing rings.
What is the most common type of packing ring made of?
Rope fibers impregnated with graphite or lead.
What kind of packing rings are not adjustable?
Ceramic or mechanical.
What is used to provided cooling and lubrication to packing rings?
A lantern ring. A small amount of water leaks out around the packing to prevent heat build up.
If a pump has been keep dry for some time, what should be done before adjusting the packing rings?
It should be ran full.
What is a problematic situation for a mechanical seal over a packing ring?
If the freeze they may be damaged and have to be replaced.
What is the most important consideration when deciding on a pump mounting and drive system?
The use that the system receives.
Pumps that are powered by a independent gasoline or diesel engine .
Auxiliary Engine - Driven Pumps
What are the most common applications for auxiliary engine driven pumps?
ARFF. Wild land apparatus. Mobile water supply apparatus. Trailer mounted fire pumps. Portable fire pumps.
Max amount of flexibility. Ideal for pump and roll. May come as a skid mount unit that provides 500 gpm. ARFF and trailer mounted may be rated up to 4,000 gpm or more.
Auxiliary Engine Driven Pumps.
Pump is driven by a drive shaft that is connected to the power take off on the chassis transmission. Most common on initial attack, wild land, and mobile water supply apparatus. Have become increasingly popular on structural pumpers.
Power Take off Drive PTO