IFSTA - Chapter 9 Flashcards
1
Q
Positive Displacement Pump
A
- Self-priming pump that utilizes a piston or interlocking rotors to move a given amount of fluid through the pump chamber with each stroke of a piston or rotation of the rotors
- Used for hydraulic pumps on aerial devices’ hydraulic systems and for priming pumps on centrifugal fire pumps
TYPES: Piston pumps, rotary pumps, rotary gear pumps, rotary vane pumps
PG 296-298
2
Q
Piston Pumps
A
- Positive-displacement pump using one or more reciprocating pistons to force water from the pump chambers
- Can provide pressures up to 1000psi for high pressure fog lines or to inject foam concentrate into a water line or manifold at a higher pressure than the water pump is creating
PG 296
3
Q
Rotary Pumps
A
- Simplest of all the fire apparatus pumps
- Use of rotary pumps is confined to small capacity, booster-type pumps; low volume, high pressure pump; and priming pumps
PG 296
4
Q
Rotary Vane Pumps
A
- Type of positive displacement pump commonly used in hydraulic systems
- A rotor with attached vanes is mounted off-center inside the pumping house
- Pressure is imparted on the water as the space between the rotor and the pump housing wall decreases
PG 298
5
Q
Centrifugal Pumps
A
- Pump with one or more impellers that rotate and utilize centrifugal force to move the water
- Most modern fire pumps are this type
PG 298
6
Q
Operation of Centrifugal Pumps
A
- Based on the principle that a rapidly revolving disk tends to throw water introduced at its center toward the outer edges of the disk
1. The IMPELLER acts as a disk receiving its water through the EYE in its center
2. This water is thrown out to the VOLUTE around the outside edge of the pump housing
3. The faster the disk is turned, the harder the water is thrown, giving the water more velocity
4. The velocity of the water is converted to pressure by confining the water within the container
PG 299
7
Q
Impeller
A
Vaned, circulating member of the centrifugal pump that transmits motion to the water
PG 299
8
Q
Impeller Eye
A
Intake orifice at the center of a centrifugal pump impeller
PG 299
9
Q
Volute
A
Spiral, divergent chamber of a centrifugal pump in which the velocity energy given to water by the impeller blades is converted into pressure
PG 299
10
Q
Three main factors influencing a centrifugal fire pump’s discharge pressure:
A
- Amount of water being discharged: if discharge outlet is large enough to allow water to escape as its thrown from the impeller and collected in the volute –> pressure build up will be minimal; If discharge outlet is small or closed –> high pressure build up
- Speed at which the impeller is turning: Increased impeller speed = greater pressure is developed; typically impeller speed squared (Ex. doubling speed of impeller –> four times as much pressure)
- Pressure of water when it enters the pump from a pressurized source (hydrant, relay, etc): water will flow through centrifugal pump even if impeller is not turning; movement of impeller increases both velocity and corresponding pressure build up of the water in the volute
PG 300
11
Q
Two Types of Centrifugal Fire Pumps
A
- Single-Stage Centrifugal Fire Pump
- Multistage Centrifugal Fire Pump
PG 300
12
Q
Single-Stage Centrifugal Fire Pump
A
- Pumps constructed with single impeller
- Provide flow capacities up to 2250 GPM
- To minimize lateral thrust of large quantities of water entering the eye of the impeller –> double-suction impeller may be used (takes in water from left and right side, to prevent any lateral thrust from having one sided intake)
PG 301
13
Q
Multistage Centrifugal Fire Pump
A
- Centrifugal pumps have an impeller for each stage mounted in a single housing
- Feature that makes multistage pumps more efficient is the capability to connect the stages in series for maximum pressure or in parallel for maximum volume by use of a transfer valve
- Pumping in PARALLEL (volume) POSITION: Each of the impellers takes water from a source and delivers it to the discharge; each impeller delivers its rated pressure while flowing 50% of its rated capacity (Ex. two-stage pump rated @ 1000GPM, 150PSI –> each impeller supplies 500GPM (1000 total) at 150PSI; max flow rating is met but volume of the pump can increase with capability of the water source
- Pumping in SERIES (pressure) POSITION: All water from the intake manifold is directed into the eye of the first impeller; first stage increases the pressure and discharges 50-70% of volume capacity through the transfer valve and into the eye of the second impeller; series position greatly increases pressure discharged, but with a loss in corresponding volume
PG 302
14
Q
Parallel (Volume) Pumping Mode capabilities
A
- When in doubt, it is best to operate in parallel (volume) mode rather than series (pressure) mode
- Parallel mode = pump is capable of supplying 100% of its rated capacity at 150PSI @ 10 feet of lift with 20 feet of suction hose while drafting
PG 303
15
Q
Clapper (Check) Valves
A
- Hinged valve that permits the flow of water in one direction only
- Check Valve is automatic version of hinged valve
- Ex. The inline valve that prevents water from flowing into a foam concentrate container when eduction pressure is disrupted
PG 304
16
Q
Wear Rings
A
Replaceable rings that are attached to the impeller and/or the pump casing to allow a small running clearance between the impeller and pump casing without causing wear of the actual impeller or pump casing material
PG 304
17
Q
Auxiliary Engine Drive Pumps
A
- EX. Pumps powered by gasoline or diesel engines independent of the vehicle-drive engine
- Most common applications: ARFF vehicles, wildland fire apparatus, mobile water supply apparatus, trailer mounted fire pumps portable fire pumps
- Pump capacity of generally 500 GPM
PG 307
18
Q
Power Take-Off Drive (PTO)
A
- Mechanism that allows a vehicle engine to power equipment such as a pump, winch, or portable tool
- Typically attached to the transmission
- Most common to initial attack, wildland or mobile water supply applications
- Allows pump-and-roll capability
- Pump capacity generally up to 500GPM, but some as large as 1250GPM
PG 307-308
19
Q
Front-Mount Pumps
A
- Fire pump mounted in front of the radiator of a vehicle and powered off the crankshaft
- Typically up to 1250 GPM
- Disadvantage: susceptibility of pump and gauges to freeze in cold weather due to their exposed position
PG 309
20
Q
Midship Pumps
A
- Mounted behind the engine and transmission
- Most common kind for modern pumpers; power can be diverted from rear axel and transmitted to fire pump
PG 309
21
Q
What speed will show on speedometer when truck is idling, pump engaged?
A
10-15mph
PG 310
22
Q
Signs that truck is successfully in pump mode?
A
- Pump indicator light
- Speedometer reading
- Listening for sound of pump engaging
PG 311
23
Q
Disadvantage of rear-mount pumps?
A
Driver/operator is more exposed to oncoming traffic than other pump locations
PG 312
24
Q
Pump Pipes and Valves
A
- NFPA 1901: requires all components of piping system be of corrosion resistant material (cast iron, brass, stainless steel, galvanized steel)
- Must be capable of withstanding a hydrostatic test of 500 PSI
PG 312
25
Q
Intake Piping
A
- NFPA 1901: pumpers with capacity of 500 GPM or less should have piping capable of flowing 250 GPM; pumpers with capacity of 500 GPM or more should have piping capable of flowing at least 500 GPM
PG 313
26
Q
Discharge Piping
A
- NFPA 1901: All fire apparatus with a rated pump capacity of 750gpm or greater must be equipped with at least TWO 2.5” discharges; apparatus with a rated pump capacity of 750gpm or less only have to have ONE 2.5” discharge
- NFPA 1901: Apparatus equipped with tanks of less than 1000gpm must have a tank fill line of at least 1” in diameter; apparatus equipped with tanks greater than 1000gpm must have a tank fill line of at least 2”
PG 315-316
27
Q
Valves
A
- Control most of the intake and discharge lines
- Most common is ball type valve that permits the full flow of water through a line with a minimum friction loss
- Most common actuator (handle) for ball type valve are either push-pull handles (T) or quarter-turn handles
- Gate valves - typically operated by hand wheel and control large diameter pipes
PG 317
28
Q
Bleeder Valve
A
- Intake line is full of air when dry, so the water coming through the line would force air into the pump, which may cause a momentary loss of prime and fluctuation to nozzle pressure
STEPS:
1. Open bleeder valve on line side of intake vale
2. Air is forced out of the hose and passes through the bleeder as the hose fills with water
3. When all air has been evacuated from the line and bleeder is discharging steady stream of water, close bleeder valve
4. Open intake valve
5. Close tank to pump valve
PG 318
29
Q
Automatic Pressure Control Devices
A
- NFPA 1901: Requires some type of pressure control device to be part of any fire apparatus pumping system
- Must operate within 3-10 seconds after the discharge pressure rises and restricts the pressure from exceeding 30psi above the set level
PG 318
30
Q
Relief Valves
A
- Sensitivity to pressure change its ability to relieve excessive pressure within the pump discharge
- Most are set to be open when the intake pressure rises more than 10psi
- Two basic types:
1. Those that relieve excess pressure on the DISCHARGE SIDE of the pump –> controls pressure that is delivered to the hoseline nozzle from the pump
(EX. when the pump discharge pressure rises higher than allowed by the pilot valve setting, the spring in the pilot valve compresses, allows needle valve to move to left, causing water to dump back into pump intake. This reduces the pressure in the tube and behind the main valve. Main valve opens and permits water to return to the intake side, reducing discharge pressure)
2. Those that relieve excess pressure on the INTAKE SIDE of the pump - Permits the pump to continue operation when pressure rises above the working, or set, pressure
(EX. Pressure rises above the set pressure, pilot valve moves, compresses its spring until opening in the pilot valve housing is uncovered. Water flows through this opening and through the bleed line, and into pump intake. This reduces the pressure on the pilot valve side of the relief valve, allowing the higher pressure on the discharge side to force the valve open. Water flows from the discharge into the intake, relieving the excessive pressure)
PG 319
31
Q
Pressure Governor
A
- Pressure control device that controls engine speed, eliminating hazardous conditions that result from excessive pressure
- Regulate engine speed to match pump discharge requirements
- Electronic governor features cavitation protection –> returns engine to idle when intake pressure drops below 30psi
PG 321
32
Q
Cavitation
A
- Condition in which vacuum pockets form due to localized regions of low pressure at the vanes in the impeller of a centrifugal pump, causing vibrations, loss of efficiency, and possibly damage to the impeller
PG 321
33
Q
Priming Device
A
Any device usually a positive displacement pump, use to exhaust the air from inside a centrifugal pump and the attached hard suction
- This creates a partial vacuum, allowing atmospheric pressure to force water from a static source through the suction hose into the centrifugal pump
PG 322
34
Q
Venturi Effect
A
- Physical law stating that when a fluid, such as water or air, is forced under pressure through a restricted orifices, there is an increase in the velocity of the fluid passing through the orifice and a corresponding decrease in the pressure exerted against the sides of the constriction.
- Because the surrounding fluid is under greater (atmospheric) pressure, it is forced into the area of lower pressure
PG 324
35
Q
Tachometer
A
- Displays the engine speed in RPMs
- Provides an experienced driver/operator with a means to identify problems during a pumping operation
PG 326
36
Q
Voltmeter
A
- Device used for measuring existing voltage in an electrical system
- Provides a relative indication of battery condition
PG 326
37
Q
Ammeter
A
- Gauge that indicates both the amount of electrical current being drawn from and provided to the vehicle’s battery
- Indicates status of the vehicle’s alternator and charging system
PG 326
38
Q
Auxiliary Cooling Devices
A
- Control the temperature of coolant in the apparatus engine during pumping operations
- Either MARINE or IMMERSION
39
Q
Which type of valve is commonly used on large diameter intakes and operated by a quarter-turn handle?
A
Butterfly valve
PG 317
40
Q
What is NOT indicated by a vacuum gauge connected to the intake side of the pump?
A
Net Pump Pressure
PG 324-325
41
Q
What are correct uses of drain or bleeder valves?
A
- Provide a discharge for air trapped in supply lines
- Drain the pump and piping in freezing weather climates
- Relieve pressure in a hoseline when both the discharge valve and nozzle are closed
PG 317-318
42
Q
What will be the result if a small amount of water is permitted to leak around the impeller shaft packing?
A
The water will prevent excessive heat buildup between the shaft and packing
PG 306
