IFSTA Chapter 9 Fire Pump Theory Flashcards
How Does a Positive Displacement pump “self Prime”
Piston or Interlocking rotors moving a certain amount of fluid through the pump chamber with the stroke of a piston or rotation of the rotors
Positive displacement pumps are what kind of flow
“machine”
Constant Flow Machine: they produce the same flow at a given speed regardless of discharge pressure.
Centrifugal pumps don’t use _________ action to force water, rather it depends on the ___ ___ ___ produced by _____ _____ to provide appropriate pressure
Centrifugal Pumps don’t use (positive action) to force water rather it depends on the velocity of the water produced by (centrifugal force)
How are positive displacement pumps used in modern apparatus along centrifugal pumps
As priming devices to get water into centrifugal pump. Removing trapped air in the centrifugal pump, water is forced into the pump by atmospheric pressure
Piston Pumps
Operate using a piston that moves back and forth in a cylinder
Types of rotary pumps
Rotary Gear or Rotary Vane
Driven by either a small motor or a clutch that extends from the apparatus drive shaft
How do rotary gear pumps operate
Gears rotate in a tightly meshed pattern inside a watertight case. Gears create tight pockets as they turn from intake to discharge.
What kind of pump is a rotary gear pump and why?
Positive displacement pump:
each pocket in the gears contains a definite amount of water, which is forced out of the pump as they turn with a positive action.
In Rotary Gear pumps what are the gears and casings made of to prevent wear and tear from debris in water
Gears: Bronze or another metal
Casing: Strong Alloy such as Cast Iron
How are rotary vane pumps built
Moveable elements that automatically compensate for for wear, maintaining a tighter fit
Most common type of pump used to prime a centrifugal fire pump
Rotary Vane Pump
Explain the works of a rotary vane pump
Rotor is mounted off center inside housing
The Vanes are free to mve within the slot where they are mounted
As the Rotor turns, the vanes are forced against the housing by centrifugal force
As vanes become worn centrifugal force causes it to extend further making it more efficient to pump air out of system
How does a rotary vane pump air out of system
As the rotor turns, air is trapped between the rotor and the casing in the pockets formed by adjacent vanes
As the vanes turn this pocket becomes smaller which compresses the air and causes pressure to build up
The Pocket becomes smaller as the vanes progress toward discharge reaching its maximum level of pressure forcing trapped air out of the pump
What happens when air is evacuated from the intake side of the pump
A vacuum is created by reduction of pressure which forces water into the pump by atmospheric pressure until it fills with water
Definition of a centrifugal pump
Pump with one or more impellers that rotate and utilize centrifugal force to move the water.
What are centrifugal pumps classified as
Nonpositive displacement pump
Why are centrifugal pumps nonpositive displacement pumps
It does not pump a definite amount of water with each revolution
The Pump imparts velocity to the water and converts it to pressure within the pump itself
Basic operation of a centrifugal pump
A rapidly revolving disk tends to throw water introduced at its center toward the outer edges of the disk
How does water move within a centrifugal pump
Impellers receive water through the eye of the pump which is thrown out to the volute around the outside edge of the pump housing.
Describe an impeller
Vaned, circulating member of the centrifugal pump that transmits motion to the water
Define the eye of the impeller
Intake orifice at the center of a centrifugal pump impeller
Define Volute
Spiral, Divergent chamber of a centrifugal pump in which the velocity energy given to water by impeller blades is converted to pressure
How does the impeller generate pressure
The speed of the impeller dictates the amount of pressure developed
The velocity of water is converted to pressure by confining the water within the container
What dictates the volume capacity of the pump
The Size of the Impeller
What does the off-center mounting of the impeller create
A water passage of gradually increasing size as it nears the discharge outlet of the pump.
The Volute
What part of the impeller confines water within its travel after contact with the vanes as its thrown out to the outside of the impeller
The Shrouds of the Impeller
Why does the increase in size in the volute matter
The increase in size reduces the velocity of water enabling the pressure to build up proportionally .
3 Main Factors that influence centrifugal pumps discharge pressure
Amount of water being discharged
Speed at which impeller is turning
Pressure of Water when it enters the pump from pressurized source
related to rpm, the increase in pressure is roughly equal to the square of the change in _________
Impeller Speed
Doubling the impeller speed will result in Four times as much pressure
What is the centrifugal pump not able to do
Unable to pump air and is not self-priming
When moving water from pressurized source, what is reflected in the discharge pressure
Incoming Pressure Changes
As water moves through the impeller by itself it increases both the velocity and the corresponding pressure build up of the water in the volute.
Two basic types of centrifugal pumps used in the fire service are
Single Stage and Multistage
In single stage pumps what phenomenon may lead to pump damage
A phenomenon of cavitation where excess capacity is not allowed to escape the impeller area
Single stage pumps have a single ______ and are rated up to ______ gpm
a Single Impeller and are rated up to 2250 gpm
Components of multi-stage pumps
Impeller for each stage mounted in a single housing. The Impellers are usually mounted on a single shaft driven by a single drive train
Measurement between the pump casing and the hub of the impeller
Limited to .01” or 25mm OR LESS
Indications of wear in impellers and pump
During pump tests when increased engine RPM is required to pump at the rated capacity
What is used to restore pump capacity instead of replacing pump
Wear Rings also known as Clearance rings in the pump casing may be replaced to maintaned the preferred spacing .
When shutting off pump discharges how is the energy dispersed
Energy from the impeller is dissipated in the form of heat as water within the pump is allowed to churn
When discharges are closed and pump has been running what can the heat in the water churning cause
Metal parts of the pump may expand, Wear rings and impellers may come in contact due to expansion creating more heat from friction and leading to serious damage to the pump
What are newer pumps equipped with to deal with overheating
A thermal relief valve that opens to allow overheated water to circulate between the pump and the main water tank or into the atmosphere
Best course of action to prevent and correct overheating
Ensure some water is moving through the pump by opening a discharge, tank fill or a circulating valve.
How to manually check for excessive pump temperature in the pump
Placing a hand on the direct pump intake pipe, if it is warm to the touch steps should be taking to lower temperatures
Describe the build between the impellers and the drive shaft
Impellers are fastened to a shaft that connects to a transfer case.
The vehicle transmission transfers the required energy to spin the impellers at a very high rate of speed
What must be maintained at the point where the shaft passes through the pump casing
A semi-Tight seal must be maintained to prevent air leaks that may interfere with the pump’s ability to conduct a drafting operation
Most common type of shaft seals used today
What do they form
Mechanical seals.
They form a tight seal without dripping and do not require periodic adjustments
How can shaft mechanical seals be maintained
What should be avoided
Operating the pump regularly to lubricate the seals
should not be allowed to freeze in cold weather
Do Not run seals waterless for any length of time as they will overheat and become damaged
Most Common type of shaft seal packing material is
Rope fibers impregnated with graphite or lead
pushed into a stuffing box by a packing gland driven by a packing adjusment mechanism
also found in ceramic or mechanical seals that are not adjustable
Packing rings found as shaft seals contact the shaft and via friction create heat, this can be avoided by including this object
A spacer, known as a lantern or slinger ring
to provide cooling via a small leak of water around the packing preventing the build up of excessive heat that may score the shaft
How is power provided to midship pump
Use of a split shaft gear case (transfer Case) located in the driveline between the transmission and the rear axle. Shifting a Gear and Collar arrangement inside the gear box to divert power from the rear axle to the fire pump
What drives the pump after transfer case is engaged
A series of gears or a drive chain/belt
What is the gear ratio in the pump set to match?
set to match the engine torque curve to the speed of the rotation required for the impeller to deliver the rated capacity of the pump.
How much faster does the impeller turn compared to the engine
One and a half to two and a half times as fast.
What prevents the transmission from switching gears as rpms are raised or lowered in the pump
A lockout feature is engaged when the transmission is in the correct gear.
What will most speedometers indicate when pump is engaged
10 to 15 mph
Primary parts of a pump piping system
Intake, Discharges, Drains and valves
What material does NFPA 1901 require pump piping components be made of
Corrosion Resistant Material
such as cast iron, brass, stainless steel and galvanized steel
Before being placed into service what exact pressure must the piping and the pump be able to withstand?
500 psi
In order to minimize pressure loss all piping and hoses must be designed to run…
as straight as possible
Why are all intake lines in a centrifugal pump located below the eye
to prevent air from becoming trapped and prevent a successful drafting operation
As the piping nears the pump what shape does it turn into and why
It tapers into a square to elimimate the water vortex within the pipe and prevent introduction of air into the pump
per NFPA 1901 how many sufficient 2 1/2” discharges should be installed
Discharge openings must be provided to flow the rated capacity of the pump
How many 2 1/2” discharges should be installed on a pump rated to 750gpm or greater
at least two 2 1/2”
per NFPA 1901 how big should be the tank fill line if the tank is less than 1000 gal
must have a tank fill line of atleast 1 inch
Pumps not equipped with a thermal relief valve will need this to prevent overheating when no water is flowing
A tank fill line can be used in conjunction with the tank-to-pump valve to circulate water through the pump.
What is a bypass valve
serves the same function as a circulator valve diverting portions of the discharge water into the tank
what are circulator and booster line cooling valves piped with
small diameter copper tubbing with limited flow capability.
Valves must be constructed ________ and _________ resistant
Airtight and wear resistant
Most common type of valve used in a fire pump
Ball-Type Valve providing the most flow of water with minimal friction loss
Attached to push pull handles or quarter turn handles
What set up gives the push-pull valve mechanical advantage
A Sliding gear tooth rack
What type valves are commonly found in large diameter discharges and intakes
Gate or butterfly valves
Gate: Operated by a handwheel
Butterfly: Operated by quarter turn handles
per NFPA 1901 all intakes or discharges that are 3 inches or greater must be equipped with these type valve controls
slow acting valve controls
Proper Order when opening an intake to introduce water into the pump and transitioning from tank
To prevent air trapped in an uncharged supply line, bleeder valves can be opened to to push air out while the hose is fully filled with water
When all air has been evacuated and the bleeder discharge shows a steady stream: The bleeder can be CLOSED, the intake valve OPENED and the tank-to-pump valve closed.
When should the master drain valve not be operated
When the pump is operating with pressure or with a vacuum on the intake. The O ring used as a gasket to maintain an airtight connection may be damaged
Per NFPA 1901 what kind of device must be available to correct a sudden change in flow
within what time should it operate
Restricts from exceeding how many psi’s
Pressure control device
required and must operate within 3 to 10 seconds after the discharge pressure rises
restricts sudden pressure from exceeding 30 psi
What shows an Automatic Pressure Control Device has been activated in a governed system.
Expelling of excess water or a yellow indicator light located at the pump panel
on (non-automatic governor systems) shows the system is controlling either the engine speed or pump pressure.
Main Feature of a Relief Valve
Sensitivity to pressure change and ability to relieve excess pressure within the pump discharge.
Two Concepts of Relief Valves
Relieve Excess pressure on the discharge side of the pump
Relieve Excess pressure on the intake side of the pump
Difference between intake and discharge side relief valves
Discharge: controls pressure delivered to hoseline nozzles
Intake: Adjustable spring-loaded pilot valve allows water from discharge to the intake chamber of the pump
Two Basic Types of intake pressure relief valves
at what psi is it recommended they opened
1: Supplied by the manufacturer and integral part of the pump intake manifold
2: Add On Device screwed onto the pump intake connection (recommended to be set to open when pressures rise above 10 psi from needed operating pressure)
what causes excessive pressure build up within the pump which will then activate a pressure governor
What device recognizes the information
Generally caused by shutting down one or more hoselines,
a tube from the discharge side of the pump transmits the resulting pressure rise to the governing device which will cut back throttle.
In Electronic Pressure Governors what is the pressure sensing element named
Pressure Transducer
How Does a pressure transducer control the pump operation
It Controls the action of an electronic amplifier that compares the pump pressure to an electrical reference point.
The Element changes the throttle setting AS NEEDED by adjusting the amount of fuel supplied to the engine.
What pressures will the electronic governor maintain and how does it protect from cavitation
To prevent cavitation it returns the engine to idle when intake pressure drops below 30 psi.
Maintains any pressure set above a specified setting and returns to idle whenever pressure drops below that point
In a Priming pump, what purposes does the oil/fluid it carries serve
With wear and tear the clearance between gears and pump case increases losing efficiency. Introducing thin film of oil/fluid allows the pump to seal these gaps
The Oil/Fluid will fill any irregularities created by sediment or debris along the housing of the pump.
Periodic operation will create lubrication and preserve the components of the pump
What must be checked regularly on the oil reservoir of the primer pump
Vent hole that is used to break siphon action. checked for dirt and debris
Two Types of Master Intake Gauges
Vacuum or Compound measuring either positive pressure or vacuum.
During a draft operation at what vacuum reading is the engine nearing its capacity and is not able to pump to supply additional lines
20 inHg
The tachometer displays the engine speed in RPM. A gradual increase in RPM required to pump the rated capacity may indicate
Wear in the pump and possible need for repair
Pump Engine coolant Temperature Indicator shows the coolant temp of the engine being used to turn the pump what can under or over temperature mean
Too Cool: engine is not working efficiently
Too Hot: engine may result in damage to mechanical parts.
While the vehicle is stationary and in pump operations auxiliary cooling devices are provided and should be used
Oil Pressure indicator shows adequate supply of oil being delivered to the critical areas of the engine that powers the pump.
what is the result and causing issue of an oil gauge showing low
The indicator is not able to show oil amount in the crankcase,
If oil level is low pressure may not be built up by the oil pump indicating equipment malfunction
Voltmeter provides a relative indication of battery condition
The ammeter shows the status of the vehicles alternator and charging system
what do these meters show when battery is ON but engine is OFF
Voltmeter shows: top voltage available when the battery is fully charged and measures the drop in voltage as accessories are used
Ammeter shows: amount of electrical current being drawn from and provided to the vehicles batteries
What is the proper name for discharge gauges and where are they to be placed in the piping
Pump Pressure Indicators
must be connected to the outlet side of the discharge valve so that pressure being shown on gauge is actually being supplied through the hose line
While pumping, When should pump discharge gate valves be adjusted
Each time the flow at the nozzle is changed.
It is necessary because pressure loss in the valve is determined by the amount of water flowing through it.
Gate valves should not be readjusted unless the nozzle is flowing
What are Engine Throttle Controls and the different types
Devices used to increase or decrease the speed of the engine that powers the fire pump
Several types of throttles available: Vernier, Switches or Push Buttons
Different types of primer controls
Can be found as Push Buttons, Toggle Switch or Pull Lever
Used to prime the pump for a draft they
How should the water level gauge be verified for accuracy during routine checks
Inspecting the fill opening to verify that the tank is full
Auxiliary cooling devices primary function is to control the temperature of coolant in the apparatus engine during pump ops. What are 2 types of aux devices.
Marine or Immersion
Describe a marine cooler
marine cooler is inserted into one of the hoses used in the engine cooling system. The Cooler features a number of small tubes surrounded by a water jacket which is connected to the discharge of the fire pump. As coolant passes through tubes in the cooler the colder water from the fire pump contacts the tubes reducing coolant temperature
Describe an immersion cooler
Immersion is mounted in a similar manner as the marine cooler with coolant passing through the body of the cooler. The water supplied by the fire pump passes through a coil mounted inside the cooler so that it’s immersed in the coolant. System is controlled by a valve at the panel to regulate the amount of cooling chosen
In extreme situations with dramatic failure of radiator hose or other cooling elements what can be done to cool pump until unit withdrawals are complete
A water stream may be directed at the engine to maintain a form of cooling briefly until units are withdrawn to safety
To correct overpressure in a rotary gear positive displacement pump, what must be included.
When the pump tries to move more water than the discharges can handle, pressure builds up. A Pressure Relief Device must be provided for excess pressure
per NFPA 1901 all intakes or discharges that are 3 inches or greater must be prevented from opening and closing in less than this many seconds and why?
3 seconds to prevent water hammer
What are compound and vacuum gauges calibrated to
Calibrated from 0 - 600 psi of positive pressure
and from 0 to 30” of mercury
