Chapter 8 Fire Service Pump Design Flashcards
The principle of pressure that explains how a priming pump can displace air and force water from a static supply into the fire pump
the second principal pressure: pressure applied in a confined liquid from an external source will be transmitted equally in all directions throughout the liquid without a reduction in magnitude
the basic operation of a piston pump
as the piston moves forward creates higher pressure opening a discharge valve and expelling compressed air,.. on the return stroke the volume increases closing the discharge due to vacuum and opening the intake drawing fluid into the intake. as the process is repeated air is displace completely
what makes piston pumps unusable for fire streams
surges of water followed by equal time with no water… can be improved with a double acting piston pump to make pulses not as noticeable, still bad
the limiting factor for output capacity in a piston pump
the volume of the cylinder, and to a lesser extent the speed of the piston but since the piston has a limit where the volume does not… capacity is dependent on volume of cylinder
problems of the piston pump
pulsating fire stream
susceptible to wear, requires close tolerances
wear reduces capacity
contamination can quickly damage pump
what makes rotary gear a positive displacement
the pockets in the gears contained a fixed volume
what dictates the pumps capacity of a rotary gear pump
the size of the pockets formed by the gears and the speed of the gear rotation
like piston pump, rotary gear pumps require very tight tolerances… to minimize damage to the pump…
the casting is made out of very hard metal and the gear is made of a softer metal…. oil is used to fill gaps to maintain tolerances
what makes rotary vane pumps much more efficient that pumping air than standard rotary gear pumps
as the vanes become worn centrifugal force causes the vanes to extend further automatically maintaining a tight fit
what type of pump do manufactures sometimes have maximum operating time for, if prime is not achieved operator should rest pump
Rotary vane
two types of rotary pumps
Rotary gear
Rotary vane
why is the increasing size of the volute necessary
the increasing size of volute is necessary because the amount of water passing through the volute increases as it approaches the discharge outlet …the gradually increasing size of the waterway reduces the velocity of the water thus enabling the pressure to build up proportionately
what makes centrifugal pump a nonpositive displacement pump
does not pump a defined amount of water with each revolution instead it imparts velocity to the water and converts that velocity into pressure with the pump casing
what are the two basic types of centrifugal pumps
single stage
two stage
what are the characteristics of a hydraulically balanced pump
- double intake impellers, canceling lateral thrust
2. discharge of volutes diverting water 180° apart, canceling radial thrust
two part of the centrifugal pump
impeller disk
casing
what determines the pumps capacity of a centrifugal pump
the diameter of the eye of the impeller, because it limits how much water can get into the pump
three main factors influencing a centrifugal pumps discharge pressure
- amount of water being discharged
- speed at which the impellers turning
- pressure of the water as it enters the pump from a pressurized source
when is volume position most commonly used
when pumping multiple large diameter supply lines are feeding a master stream device
what part of the pump contains water and confines it in order to convert velocity into pressure
casing
the amount of discharge pressure of the pump can develop is directly dependent upon ____
the volume of water it is discharging… the greater the volume of water being flowed, the lower the discharge pressure will be
The greater the impeller speed, the greater the pressure. This increase in pressure is approximately equal to ___
the square of the change in impeller speed. doubling the impeller speed quadruples the discharge pressure
what are the two basic types of centrifugal pumps
single stage
two stage
what are the characteristics of a hydraulically balanced pump
- double intake impellers, canceling lateral thrust
2. discharge of pollutants diverting water 180° apart, canceling radial thrust
characteristics of a two-stage centrifugal pump
- mounted on a single shaft
- driven by a single power source
- identical in size and design, having the same capacity
another name for two-stage centrifugal pump’s changeover valve
transfer valve
pumping in volume, parallel
both impellers take water on the intake and delivered to the discharge simultaneously each impeller delivers the pumps rated pressure while flowing half of its capacity
when his volume position most commonly used
when pumping multiple large diameter supply lines are feeding a master stream device
pumping in pressure, series
water from the intake goes into the eye of the first impeller increases the pressure from 50 to 70% volume capacity into the eye the second impeller second impeller, increases the pressure and delivers water at higher pressure to the discharge…. pressures much higher than in parallel… total volume is limited to the amount one impeller can supply
the pressure position is most commonly used when…
supplying attack lines especially when operating from the apparatus tank water
what is the rule of thumb for deciding between pressure and volume positions
valve stays in the pressure position until it’s necessary to supply more than one half of the rated volume capacity of the pump
due to advances in design and efficiency the rule of thumb in deciding between pressure and volume positions no longer applies most manufacturers state….
pump may remain in the pressure position until it is necessary to flow more than 70% of the rated volume capacity,…. at lower flows operating the pressure position reduces load on the engine (rpm)
at the pump operator is not sure which settings should be used ___ is better than ___
volume (parallel) is better than pressure ( series)
volume position may make attaining a higher pressures difficult but will be able to supply 100% of the pumps rated capacity at 150 PSI
was a maximum net pump discharge pressure at which changeover should be operated in most cases
75 psi
what is a danger in performing the transfer in the middle of an operation
switching from volume to pressure immediately doubles discharge pressure
many power operated changeover valves operate at pressures as high as
200 psi
centrifugal pumps with more than two impellers may be referred to as
three or four stage pumps
what are the four most common pump drive arrangements on a modern fire apparatus 5
- auxiliary engine driven pumps
- power takeoff PTO driven pumps
- front mounted driven pumps
- midship transfer driven pumps
- rear mount pumps
Auxiliary engine driven pumps receive their power from the separate engine independent of the engine used to propel the vehicle…. examples of application
- ARFF
- wild land fire apparatus
- mobile water supply apparatus
- trailer mounted fire pumps
- portable fire pumps
auxiliary engine driven pumps are preferred when departments want to have the ability to (2)
- pump and roll
2. place a fire pump remote from an apparatus
auxiliary driven pumps used for wild land apparatus typically are powered by engines with less than ___hp in a pump capacity of __ or less
50hp
400 GPM
what is the one inherent drawback for auxiliary driven pump
additional maintenance for the driver and department mechanics to engines
PTO driven pumps powered by driveshaft connection to the PTO on the chassis transmission has an optimal design when
minimum of angles in the drive shaft between the PTO connection in the pump casing
how does PTO permit pump and roll operations
it receives its power from idler gear in the chassis transmission
what is the primary difference between a PTO and front mount pump
the location of the pump on the apparatus and the location of the connection for the driveshaft that powers the pump
the most common gear ratios for front mounted pump
1:1 and 2.5:1
to accommodate a front mount pump the front bumper is moved
3 to 5 feet out
front mount pump is engaged and controlled from the pump location putting the operator in a vulnerable spot …because of this what is essential
to lock is essential to prevent the road transmission from being engaged… a warning light in the cab alerts the driver that the pump is engaged
2 disadvantages of a front mount pump
susceptible to freezing
susceptible to damage from collision’s
the most common mounting arrangement of for modern pump apparatus
midship transfer drive, bounded laterally across the frames behind the transmission
in a midship transfer drive what supplies power to the pump
split shaft gear case
the gear ratio on a midship transfer drive is calculated so the impeller turns faster than engine, how much faster
1.5-2.5 X faster
with the engine idling and the pump engaged, on a midship transfer valve what will the speedometer read
10 to 15 mph, some engines don’t do this
two disadvantages to the midship transfer driven pumps
no pump and roll
possible for gears to not complete their travel vehicle begin to move as throttle is increased… to prevent this lights on the dash indicate shift has been made
two disadvantages to the midship transfer driven pumps
- no pump and roll
- possible for gears to not complete their travel vehicle begin to move as throttle is increased… to prevent this lights on the dash indicate shift has been made
what are some advantages to a rear mounted pump
distributes weight more evenly
more compartment space for tools
major disadvantage of a remounted pump
driver exposed to oncoming traffic
two ways to power the rear mounted pump
PTO
split shaft transmission
NFPA 1901 requires fire apparatus to have pressure control devices. what does the standard require
after discharge pressure rises at least 30 psi, the device must operate in 3-10s. a yellow indicator light on the pump panel must illuminate, indicating pressure control
basic types of pressure control devices 2
relief valves
pressure governors
pressure relief valve’s are intended to reduce the possibility of water hammer damaging the pump and hose lines when…
valves and nozzles are close to quickly
the most common type of discharge pressure relief else is the adjustable spring controlled pilot valve
- when the pump discharge pressure exceeds the pilot valve setting the spring compresses allowing a needle valve to open causing water to dump….
back to the intake side of the pump
what are the two basic types for intake pressure relief valves
- supplied by the pump manufacturer as an integrated part of the pump
- add-on device screwed into the pump intake connection
is generally recommended the intake relief valve be set to
10 psi above desired operating pressure
what is the basic operating principle of pressure governor
regulates the engine power output to match the pump discharge requirements
electronic governor has a control knob that the operator can set to maintain any pressure above
50 PSI
how does an electronic governor protect the pump against cavitation
by returning the engine to idle when the pump INTAKE pressure drops below 30 psi
anytime the discharge pressure drops below 50psi, what does the electronic governor do
returns the engine idle
what is the major advantage of a electronic governor over its mechanical counterpart
mechanical governors reduce engine RPM in order to lower the discharge pressure, this briefly lowers all discharge line working pressures…. electronic governors adjust the engine RPM but maintain a steady discharge pressure on lines that are still flowing
three categories pump priming devices
- vacuum
- exhaust
- positive displacement
how to vacuum primers work
they make use of the vacuum already present in the intake manifold of any gasoline engine, bay utilize a small hose connected between the intake manifold on the intake side of the fire pump
line between the engine manifold and the pump intake on a vacuum primer has a check valve that protects against two potentially dangerous condition
prevents explosive gas from entering fire pump
prevents water from being drawn into the intake manifold
when does the vacuum primer work best
engine vacuum is at maximum near idle speed, primer works best at low engine RPM
problems with an exhaust primer
require high engine RPM
not very efficient
require a great deal of maintenance, due to exhaust
most modern apparatus and what type of priming device
electric motor positive displacement primer
what function does the oil supply to a positive displacement pump serve
as pump wearers thin film of oil seals gaps
oil acts as a preservative for metal parts
were the two types of auxiliary coolers found on fire apparatus
marine type
immersion type
described the operation of a Marine type auxiliary cooler
marine type cooler inserted in one of the engines cooling hoses so that circulating coolant must travel through it… the cooler contains a number of small tubes and water jacket that surrounds the tubes is connected to the fire pump discharge …when the pump is operating water from the pump can circulate through this water jacket…. engine coolant contacts metal jacket, metal contacts water cooling
described the operation of an immersion type cooler
in the immersion type cooler water from the fire pump passes the coil mounted inside the cooler so that it is immersed in coolant….. as hot coolant passes the cool water coil heat is exchanged
what is the tolerance between the impeller in the casing
1/100 of an inch, any increase in this opening lessens the pump effectiveness
what is an indication that wears becoming a problem
if running the pump at rated capacity requires an engine RPM substantially higher than the one listed on the UL pump plate
what is the name of the device inserted into the pump casing to maintain the desired spacing between the impeller and casing
clearance rings
lantern ring
spacers supplied with packing, provides cooling lubricant. lantern ring allows a small amount of water to leak around the package preventing excess heat buildup
in the piping system must be able to withstand a hydrostatic test of ___psi before being placed into service
500psi
the two routes through which water may enter the fire pump
- piping from the water tank to the pump
2. piping that connects the pump to an external water supply
NFPA 1901 states that piping should be sized so that
capacity 500gpm can get ___from tank to pump pipe.
If capacity over 500gpm ( so 750) then ____ from tank to pump
250gpm
500gpm
fire departments that want the capacity for initiating blitz attacks are equipping pumping apparatus with what size tank pump line
4”
what is the benefit for a check valve on the tank to pump line
prevents pressurized water entering the tank through open tent to pump valve thus preventing over pressurization of tank
what is the reason for having all intake pipes located below the eye of the impeller
any air trapped in the pump during priming can prevent successful drafting
intake pumping is round at the intake hose connection but as it nears the pump it typically tapers to a square cross-section….why
eliminate the vortex that may occur in water that flows through circular piping …a vortex could introduce air into the pump
pumps with a capacity of 1500 GPM may require ____large connection to each intake location
more than one
auxiliary intakes are provided any time the pump is receiving water from
medium diameter supply lines,from the hydrant or know the pumper ….most often these are gated to an half inch hose couplings
2.5” pipe 90° bends or T fittings, may limit flow through these intakes to ___ likewise,
if 3”pipe is used and care is given to the fitting and design flow may be as much as ___
250 gpm or less
450 gpm
auxiliary intakes are provided any time the pump is receiving water from
medium diameter supply lines, from the hydrant or another the pumper ….most often these are gated to an half inch hose couplings
most fire apparatus have one 2.5”or larger discharge for every ____gpm of rated pump capacity
250gpm
NFPA 1901 requires that discharges of 1.5”, 1.75”, and 2” be supplied by piping at least ___
2”
large diameter discharges (4-5”) are supplied commonly by
4/5” piping and valves
in a two-stage pump where does the tank refill line get its flow from
the first stage, to ensure reduced pressure
what is the issue when using tank refill to prevent overheating
in a two-stage pump the refill pipe coming off the first stage, overheating can still occur in the second stage
use the circulator valve…acts as discharge dumps water on ground
NFPA 1901 requires all pounds on intakes or discharges 3 inches or greater to be equipped with slow acting valve control … this prevents fully opening from close position in less than
3s
what is the most common valve type
ball valve
gate or butterfly valves are most commonly used for
large diameter intake and discharges
drain should not be opened when the pump is in operation doing so will
damage the O-ring gasket
whenever using pump drain, the operator should also do what
open a discharge valve, if not vacuum will hold some water in the pump
what is the range for master intake and discharge gauges
0 to 30 inches of mercury (vacuum)
0 to 600 psi
what is the maximum capacity when pumping from draft
as a vacuum reaches 20 inches the pump nears its maximum capacity and cannot supply any additional lines
what is engine oil pressure indicator not a measurement of
is not a measurement of oil level in the crank case
flowmeters are pretty particularly advantageous when supplying ____
master stream devices or hoselines with automatic nozzles
what are the two common types of flowmeter sensors
spring probe and paddlewheel
Auxiliary engine driven pumps receive their power from the separate engine independent of the engine used to propel the vehicle…. examples of application 5
- ARFF
- wild land fire apparatus
- mobile water supply apparatus
- trailer mounted fire pumps
- portable fire pumps
auxiliary driven pumps used for wildland apparatus typically are powered by engines with less than ___hp in a pump capacity of __ or less
50hp
400 GPM
what is the one inherent drawback for auxiliary driven pump
additional maintenance for the driver and department mechanics, 2 engines
major disadvantage of a rear mounted pump
driver exposed to oncoming traffic
what are the two basic types for intake pressure relief valves
- supplied by the pump manufacturer as an integrated part of the pump
- add on device screwed into the pump intake connection
anytime the discharge pressure drops below 50 psi, what does the electronic governor do
returns the engine idle
what is the major advantage of an electronic governor over its mechanical counterpart
mechanical governors reduce engine RPM in order to lower the discharge pressure, this briefly lowers all discharge line working pressures…. electronic governors adjust the engine RPM but maintain a steady discharge pressure on lines that are still flowing
how to vacuum primers work
they make use of the vacuum already present in the intake manifold of any gasoline engine, by utilize a small hose connected between the intake manifold on the intake side of the fire pump
most modern apparatus and have what type of priming device
electric motor positive displacement primer
what function does the oil supply to a positive displacement pump serve
as pump wears, thin film of oil seals gaps
oil acts as a preservative for metal parts
piping system must be able to withstand a hydrostatic test of ___psi before being placed into service
500psi
auxiliary intakes are provided any time the pump is receiving water from
medium diameter supply lines, from the hydrant or another the pumper ….most often these are gated 2.5” hose couplings
2.5” pipe 90° bends or T fittings, may limit flow through these intakes to ___ likewise,
if 3” pipe is used and care is given to the fitting and design flow may be as much as ___
250 gpm or less
450 gpm
NFPA 1901 requires all valves on intakes or discharges 3 inches or greater to be equipped with slow acting valve control … this prevents fully opening from close position in less than
3s
