IFSTA - Chapter 9 Flashcards
Positive Displacement Pump
- 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
Piston Pumps
- 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
Rotary Pumps
- 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
Rotary Vane Pumps
- 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
Centrifugal Pumps
- 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
Operation of Centrifugal Pumps
- 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
Impeller
Vaned, circulating member of the centrifugal pump that transmits motion to the water
PG 299
Impeller Eye
Intake orifice at the center of a centrifugal pump impeller
PG 299
Volute
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
Three main factors influencing a centrifugal fire pump’s discharge pressure:
- 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
Two Types of Centrifugal Fire Pumps
- Single-Stage Centrifugal Fire Pump
- Multistage Centrifugal Fire Pump
PG 300
Single-Stage Centrifugal Fire Pump
- 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
Multistage Centrifugal Fire Pump
- 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
Parallel (Volume) Pumping Mode capabilities
- 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
Clapper (Check) Valves
- 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
Wear Rings
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
Auxiliary Engine Drive Pumps
- 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
Power Take-Off Drive (PTO)
- 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
Front-Mount Pumps
- 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
Midship Pumps
- 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
What speed will show on speedometer when truck is idling, pump engaged?
10-15mph
PG 310
Signs that truck is successfully in pump mode?
- Pump indicator light
- Speedometer reading
- Listening for sound of pump engaging
PG 311
Disadvantage of rear-mount pumps?
Driver/operator is more exposed to oncoming traffic than other pump locations
PG 312
Pump Pipes and Valves
- 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