Chapter 8: Fire Service Pump Design Flashcards
Most modern apparatus still utilize some form of this type of pump as a secondary mechanism for drafting:
Positive Displacement Pump
The process of drafting is based on what principle of pressure?
The 2nd principle:
Pressure applied on a confined liquid from an external source will be transmitted equally in all directions throughout the liquid without a reduction in magnitude
What is the operating principle of a piston-type pump?
A piston moves back and forth inside a cylinder
Which piston pumps are not able to produce a usable fire stream because no water flows on the return stroke?
Single-acting piston pump
This piston pump has 2 additional valves that enable the pump to receive and discharge water on each stroke of the piston?
Double-acting piston pump
The output capacity of a piston pump is determined by:
The volume of the cylinder and the speed of the piston travel
These pumps provided a more uniform discharge because their cylinders were arranged to reach their peak flows at different points in the cycle:
Multicylinder piston pumps
What design elements were present on the cylinder of piston pumps that were particularly common on Ahrens-Fox pumpers?
A pressure dome
The piston pump has not been used as the primary fire pump since the:
1950’s
In addition to the problems of a pulsating fire stream, piston pumps are very susceptible to:
Wear and tear, thus making them maintenance intensive
What pumps were commonly used in the ’60s and ’70s for high-pressure, low-volume applications?
John Beam high-pressure pumps
The John Beam high-pressure pumps provided pressures up to ____ psi for high-pressure fog lines that typically flowed less than ___ gpm:
1,000 psi
15 gpm
Where would you find high-pressure, low-volume pumps in the fire service today?
Wildland firefighting
This type pump has the simplest operational design of all fire pumps:
Rotary-type positive displacement pumps
What type of pump do most modern fire apparatus use to today as a priming pump for the fire pump?
Rotary-type positive displacement pump
What are the 2 styles of rotary-type positive displacement pumps are there?
Rotary gear
Rotary vane
This rotary-type pump consists of 2 tightly meshed gears that rotate inside a water tight case:
Rotary gear
The rotary gear pump is a positive displacement pump because:
Each pocket in the gears contains a fixed volume
What does the rotary gear pumps capacity depend on?
The size of the pockets formed by the gears and the speed of the gear rotation
To minimize damage to the pump casing, most rotary gear pumps have gears made of:
Bronze or other soft metal
What types of metals are used for the pump casing of rotary gear pumps?
Cast iron or steel
This rotary pump has a set of vanes that are free to move within the slot where they are mounted:
Rotary vane pump
The rotary vane pump has a rotor that is mounted _________ inside the pump casing. The distance between the rotor and the casing is much greater at the _________ area:
Off-center
Intake
What self-adjusting feature does the rotary vane pump possess that makes it much more efficient at pumping air than the rotary gear pump?
When the surface of the vane that contacts the casing becomes worn, centrifugal force causes the vane to extend further, thus automatically maintaining a tight fit
As with all positive displacement pumps, the air being evacuated from the intake side causes a reduced pressure. When this happens, what forces water into the pump?
Atmospheric Pressure
This is the primary fire pump on all fire apparatus today:
Centrifugal pump
Why is the centrifugal pump not considered a positive displacement pump?
Because it does not pump a definite amount of water with each revolution
Centrifugal pumps impart _________ to water and then converts it to ________ within the pump casing:
Velocity
Pressure
What are the disks called inside of centrifugal pumps?
Impellers
On a centrifugal pump, the faster the impeller turns, the more ________ it imparts to the water:
Velocity
In a centrifugal pump, the amount of pressure created depends on:
The speed of the impeller
What are the 2 primary parts of a centrifugal pump?
The impeller and the casing
What speeds of the impeller are common depending on the design of the pump and the amount of pressure or volume desired?
2,000 to 4,000 rpms
The passage to the pump’s discharge on a centrifugal pump is called the:
Volute
What 3 main factors influence a centrifugal fire pumps discharge pressure?
- The amount of water being discharged
- The speed at which the impeller is rotating
- The pressure of the water entering the pump
If all other factors remain constant, the mount of discharge pressure a centrifugal pump can develop is directly dependent upon:
The volume of water it is discharging
The greater the volume of water being flowed, the ______ the discharge pressure will be:
Lower
The increase in pressure is approximately equal to the _______ of the change in impeller speed:
Square
If all other factors remain constant, doubling the speed of the impeller will __________ the discharge pressure:
Quadruple
Why can water flow freely through a centrifugal pump even if it is not turning?
Because it has no mechanical blockage between the intake and discharge sides of the pump
The centrifugal pumps’s ability to create pressure on water is also due in part to water’s being:
Incompressible
Why can a centrifugal not pump air out of the discharge?
Because air is compressible
What are the 2 basic types of centrifugal pumps used in the fire service?
Single-stage and two-stage
A single-stage centrifugal pump only contains 1 ______ within its pump casing?
impeller
In the days when most apparatus were powered by gasoline engines, the volume capacity of single stage pumps were limited to ________ gpm:
1,250 gpm
Modern pumpers with diesel engines and single-stage pumps are capable of producing up to _______ gpm:
2,000 gpm
To minimize the stresses and lateral thrust created by large quantities of water entering the eye of the impeller, engineers designed a:
Double intake impeller
What is developed as the water is delivered to the discharge outlet because the impeller turns at a very high rate?
Radial thrust
Radial thrust is canceled by:
Removing the water at 2 places and directing it in opposite directions
What are the 3 characteristics of two-stage centrifugal pumps?
- They are usually mounted on a single shaft
- They are driven by a single power source
- They are usually identical in size and design and have the same capacity
In two-stage pumps, when working in parallel impellers are able to deliver more:
GPM
In two-stage pumps, when working in series the impellers are able to deliver more:
Pressure
In parallel mode, each of the impellers can deliver the pump’s rated pressure rated pressure while flowing _____ of its rated capacity:
Half
The volume (parallel) position is most often used when:
Pumping multiple or large diameter supply lines or feeding master stream devices
Depending on the manufacturer, the first impeller while pumping in series discharges from ____ to ____ percent of the volume capacity through the changeover valve and into the eye of the 2nd impeller:
50 to 70 percent
The pressure (In series) position is most often used:
When supplying attack lines, especially when operating from the apparatus water tank
The process of switching between pressure and volume mode is sometimes referred to:
Changeover
Historically, the fire service has taught the rule of thumb that the changeover valve stays in the _______ position until it is necessary to to supply more than ________ the rated volume capacity of the pump:
Pressure position
1/2
Advances in design and efficiency have allowed most pump manufacturers to specify that the pump may remain in pressure mode until it is necessary to flow more than ___ percent of the rated volume capacity:
70 percent
If the pump operator is not sure which position to use, which one should he default to?
Volume (parallel) position
In parallel position, the pump will be capable of supplying _____ percent of the rated volume at ____ psi:
100%
150 psi
In most cases, the recommended maximum pressure to perform changeover should not exceed ____ psi:
75 psi
What should the driver do when idling down to perform changeover is necessary?
Coordinate it with the fire attack group
Switching from volume to pressure mode immediately _________ the discharge pressure:
Doubles
Newer pumps utilize power-operated changeover valves that can be driven by one of these ways:
- Electricity
- Pressure
- Vacuum (Gasoline powered vehicles)
- Water pressure itself
Many power-operated changeover valves operate at pressures as high as:
200 psi
Centrifugal pumps with more than 2 impellers have and continue to be used most often found in fire departments that:
Protect tall high-rise structures
The centrifugal pumps that are used to protect high-rises and have as many as 4 impellers are capable of producing pressures up to ______ psi:
1,000 psi
What is the most important consideration when deciding how and where a pump is to be mounted on an apparatus?
The pump’s expected use
What are the most common pump drive arrangements on modern fire apparatus?
- Auxiliary-engine driven pumps
- Power take-off (PTO) driven pumps
- Front-mount driven pumps
- Midship transfer driven pumps
- Rear mount pumps
Auxiliary-engine pumps receive their power from:
A separate engine independent of the engine used to propel the truck
Auxiliary-engine driven pumps are more likely to be found in these applications:
- ARFF apparatus
- Wildland trucks
- Mobile water supply trucks
- Trailer-mounted fire pumps
- Portable fire pumps
Auxiliary-engine driven pumps are preferred when the department wants either the ability to:
Pump and roll or the ability to place a fire pump remote from the truck
Pump and roll operations are common in:
ARFF and Wildland firefighting