Ch. 9 Fire Pump Theory

Question 1

Positive displacement pumps

Answer 1

-Used as priming device to get water into centrifugal pump
-Double-acting piston pump- The addition of two or more valves allows pump to both receive and discharge water on each pump making it more useful for pumping
-“Constant flow machines” same flow at a given speed regardless of discharge pressure
-They can pump air therefore used as a priming device to get water into centrifugal pumps during drafting operations
-Positive action takes place all water and air are forced out of the pump body with each operation cycle
-Use oil supply for two reasons= seals/fills gaps in housing and perseveres metal parts
-Piston/rotary pumps

Question 2

Piston Pumps

Answer 2

-Operate using piston that moves back and forth in a cylinder
-Pressure cause intake and discharge valves to operate and cause movement of air, water, and foam
-Provide pressure up to 1,000 psi

Question 3

Rotary Pumps

Answer 3

-Simplest type of fire pump
-low volume high pressure
-Rotary gear or rotary vane

Question 4

Rotary Gear

Answer 4

-two gears that rotate in a tightly meshed patter inside watertight case
-as tooth reaches discharge air or water is forced out
-Total amount of water discharged depends on rotation and size of pockets in gear
-Made of bronze and other soft metals

Question 5

Rotary Vane

Answer 5

-Most common to prime centrifugal pumps
-Rotor mounted off center inside housing
-Constructed of moveable elements that automatically compensate for wear, maintaining tighter fit.
-Vanes are free to move within slot (they will extend out to keep the seal)
-More efficient at pumping air
-prone to failure if not exercised regularly

Question 6

What makes a Centrigual Pump a nonpositive displacement pump

Answer 6

-it does not pump a definite amount of water with each revolution
-It imparts velocity to the water and converts it to pressure within the pump

Question 7

Principles of Operation and Construction of Centrifugal Pumps

Answer 7

• Operation of a rapidly revolving disk to throw water introduced at its center toward the outer edge
• The faster the disk is turned, the farther the water is thrown
• Made up of two parts:
  1. Impeller- transmits energy in the form of velocity to the water
  -Water is introduced from the intake into the eye of impeller
  -Larger the eye greater the flow
  -Volume capacity is dictated by size of impeller
  2. Casing- collects the water and confines it in order to convert the velocity to pressure
• Volute- water passage that increases in cross-sectional area as it nears the discharge outlet of pump
• Three main factors that influence discharge pressure:
  -Amount of water being discharged
  -Speed at which impeller is turning
  -Pressure of water when it enters pump (intake side)
  -The greater the volume of water the lower discharge pressure
  -Greater speed impeller greater pressure developed

Question 8

Single Stage Centrifigul Pump

Answer 8

(front mount pumps, power take off, midships)
-Newtons third law for every action there is an equal and opposite reaction
-The double suction impeller takes water in front both sides; the reaction begin equal and opposite cancels the later thrust
-Stripping edges in the opposed discharge volutes divert water 180 degrees apart
-Water being removed at two places and traveling in opposite directions cancels the radial thrust

Question 9

Multistage Centrifigul Pumps

Answer 9

• Has Impeller for each stage mounted within single housing
• Capability of connecting the stages in series for maximum pressure or in parallel for maximum volume by use of transfer valve
• Pumping in parallel (volume) position: each of the impellers is capable of delivering its rated pressure while each flowing 50% of the rated capacity
• Pumping in series (pressure) position: all the water from the intake manifold is directed into the eye of first impeller. Discharge 50-70% of the volume capacity through the transfer valve and into the eye of second impeller
• Change over- Switching between pressure and volume in multistage pump
  -Switching from volume to pressure results in doubling of the previous discharge pressure
  -Maximum net pump discharge pressure at which the transfer valve may be safely operated varies by manufacturer
  -While in parallel position, it can supply 100% of the rated capacity at 150 psi
  -Many power transfer valves operate at 200 psi and pose risk to personnel and equipment

Question 10

Pump Wear Rings and Packing

Answer 10

-Opening between impeller and casing limited to 1/100 (.25mm)of an inch or less
-Wear Rings- replaceable rings that are attached to the hub of impeller or pump casing to allow small running clearance between impeller and pump without causing wear
-When discharge is closed energy being supplied is dissipated to heat as water in pump is allowed to churn
-Water may become hot and the metal parts may expand
-Thermal relief valve in newer engines allow heated water to circulate between pump
-Mechanical seals DO NOT DRIP are most common, form tight seal
-Packing material is composed of rope fibers impregnated with graphite or lead
-Packing rings are primarily used in older fire pumps
-Packing gland can be tightened to control leaks
-Lantern rings provide cooling between packing rings and shaft

Question 11

Auxiliary Engine Driven Pumps

Answer 11

-Pump pressure is independent from the drive system make it ideal for pump and roll operations
-Pump capacity of skid units is generally 500 gpm or less
-Powered by gasoline, or diesel engine independent of vehicle drive engine
-Used in airport rescue, wildland, mobile water supply, trailer mounted pumps, and portable fire pumps

Question 12

Power Take Off Drive

Answer 12

• The pump is driven by driveshaft connected to the power take-off
• Pump and roll
• The mounting of the pump offers shorter wheel base, additional room for compartments
• speed of the shaft independant of the gear of road transmission, but is under the control of the clutch
• The PTO pump does permit pump and roll operations, but is not as effective as a separate engine unit
  -Use pressure gauge mounted in cab rather than speedometer
  -Lowest gear makes maintaining the balance between speed and pressure easiest
  -Conventional units limited the capacity of the pump to 500 gpm
• “Full torque” power take-off permits pumps as large as 1,250 gpm

Question 13

Front-Mount Pumps

Answer 13

-Gear box and clutch connected by drive shaft to the front of crankshaft
-Pump is mounted between the bumper and the grill
-Step up gear ratio is set to match the torque curve of the engine to the rotation speed
-Required for the impeller to deliver the pumps rated capacity
-Pump capacity 1,250 gpm
-Disadvantages:
1. in cold: pump and gauges freezing
2. in warm: can overheat due to obstructing airflow
-Engaged to operate from pump location in front of apparatus
-Warning light in cab to notify driver that pump is engaged
-Vulnerable to damage from minor impact

Question 14

Midship Pumper

Answer 14

-Most common drive and mounting arrangement in use
-Power is supplied to the pump through the use of a split shaft gear case (transfer case) located in the driveline between the transmission and rear axle
-Pump is driven by gears or a drive chain or belt
-The gear ratio is set to match the engine torque curve to the speed of the rotation required for the impeller to deliver the rated capacity to pump
-Ratio is arranged that the impeller turns faster than the engine, usually 1.5-2.5 times as fast
-Maximum capacity depends on engine horsepower and size of pump
-Rated anywhere from 500 to 2,250 gpm
-Transfer case can be controlled from inside the cab
-With engine idling and the pump engaged most speedometers read 10 to 15 mph or may be 0 in new trucks

Question 15

Rear Mounted Pumps

Answer 15

• Advantages:
  1. helps with weight distribution and more compartment space
  2. more usable compartment space
• Disadvantage:
  1. driver is exposed to oncoming traffic

Question 16

Pump Piping and Valves

Answer 16

-Primary piping system are intakes, discharges, pump drains, and valves
-Must be made of a corrosive resistant material
-Piping must be able to withstand a hydrostatic test of 500 psi
-Piping should run as straight as possible

Question 17

Intake Piping

Answer 17

-Piping should be sized so pumpers with capacity of 500 gpm or less should be capable of flowing 250 gpm from booster tank
-Greater than 500 gpm should be able to flow at least 500 gpm
-Most pumpers today have a tank to pump lines 4 inches in diameter
-All are equipped with check valves
-All intake lines in a centrifugal pump are located below impeller eye
-As pipe nears the pump it tapers off the a square shape to eliminate the vortex that may occur in water that flows through circular piping which can result in air in the pump
-Pumpers rated greater than 1,500 gpm capacity require more than one large intake connection at each location
-Front and rear intakes on midship pump are really auxiliary intakes
-Main intakes on midship pump are on the sides
-If the pipe is no larger than 2 ½ inches and it contains 90-degree bend or T fittings, friction loss may limit the flow through these intakes to 250 gpm 3-inch pipe may flow as much as 450 gpm
-Prime pump by removing air from pump which lowers atmospheric pressure within pump casing

Question 18

Discharge Piping

Answer 18

• Sufficient number of 2 ½-inch discharge openings must be provided to flow rated capacity of pump
  -750 gpm rated pump or greater must have at least two 2 ½-inch discharges
  -Pumps less than 750 gpm are required to have only one 2 ½-inch discharge
• Discharges to which 1 ½-, 1 ¾-, or 2-inch handlines must be supplied by 2-inch piping
• usually equipped w/ locking ball valves, should be designed to be easily operable at pressures up to 250 psi
• *Tank 1,000 gallons or less must have tank fill line 1-inch in diameter
• Tank 1,000 gallons or larger must have a 2-inch tank fill line
• Discharges larger than 2 ½” must not be located on pump panel due to hazard if connection failed*
• Circulator valve: help prevent pump from overheated, connected to the discharge side of the pump, enabling water to be dumped into the tank or outside the tank onto the ground

Question 19

Valves

Answer 19

Circulator Valve- Enables water to be dumped into tank or outside the tank onto ground
-Most common type is ball valve that permits full flow through the lines with a minimum friction loss
-Ball valve is open by a 90-degree movement of handle
-Gate or butterfly valves are more common on large diameter intakes
-Gate valves operated by a handwheel
-Butterfly valve operated by quarter-turn handles
-All valves on intake and discharges that are 3-inch or greater must be equipped with slow acting valve controls
-taking at least 3 seconds to open/close
-This prevents movement from fully open to fully closes in less than three seconds to minimize water hammer

Question 20

Pump Drains

Answer 20

-Will drain the hose side after the discharge valve and nozzle are both closed
-Are on the line side of control valve
-Bleeder Valve on Gated Intake- Allows change-over to be made without interrupting fire streams
-Must be supplied at the lowest point on pump and the lowest point on each line connected to it
-Master drain should not be opened with pressure or vacuum on the intake can damage the O ring

Question 21

Automatic Pressure Control Devices

Answer 21

-Volume of water moving through pump may change when nozzle is closes
-Multiple attack lines change in flow on one line can cause pressure surge
-Device must operate in 3-10 seconds after the discharge pressure rises and restricts the pressure from exceeding 30 psi
-yellow light on pump panel must illuminate

Question 22

Relief Valves

Answer 22

• Some relieve pressure on discharge and some relieve pressure on intake
• Most common relief valve uses a spring-controlled pilot valve
• When the pump discharge pressure rises higher than allowed by the pilot valve setting, the spring in the pilot valve compress and cause water to dump back into pump intake relieving excess pressure
• Intake pressure relief valves- Are intended to reduce the possibility of damage to the pump and discharge hose lines causes by water hammer
  -Intake relief valves usually set to open when intake pressure rises more than 10 psi above desired operating pressure

Question 23

Pressure Governer

Answer 23

• Pressure activated to adjust engine throttle
• When excessive pressure builds up, a tube from discharge side of pump transmits the resulting pressure rise to governing device which then cuts back the throttle
• Pressure governor- Can be used in connection with throttle control
• Electric governor- Will maintain any pressure set on the control above a specified setting
  -Returns engine to idle speed when pressure drops below that point
  -Cavitation protection mode returns engine to idle if intake drops below 30 psi
  -Major advantage: closed discharge line engine rpm adjusted which lowers discharge pressure for all lines as rpm is lowered

Question 24

Primers

Answer 24

• Positive Displacement Primer- Uses oil to seal gaps between gears and the case to fill irregularities in the housing caused by sediment or debris
• Oil-Less Primers- Most new pumpers are equipped and constructed of materials that do not require lubricant
  -Environmentally friendly and does not require lubricant
• Exhaust Primers- Found on skid-mounted pumpers or older
  -Same principal as foam eductor
  -Exhaust gases from vehicle engine are prevented from escaping to the atmosphere by exhaust deflector
  -High engine RPM required to create vacuum
• Vacuum Primers- Simplest device that makes use of vacuum already present in intake manifold
  -works best at low RPM
  -Line is connected from intake manifold from engine to intake of fire pump with a valve connected in the line to control it
• Air Primers- Becoming more popular
  -Uses compressor to supply an airline to jet pump which creates venturi effect that primes pump using no moving parts or lubricants

Question 25

Pump Panel Instruments

Answer 25

• Engine fuel gauge will be located on pump panel but not required
• Master Intake and Discharge Gauge
  -Provides indication of the vacuum present at the intake of pump during priming
  -Master intake (vacuum or compound) must be connected to intake side
  -Calibrated 0-600 psi positive pressure 0-30 mercury negative side
  -Vacuum approaches 20-inches pump is near max capacity and is not able to supply anymore lines
  -The pump discharge pressure gauge registers the pressure as it leaves the pump but before it reaches the gauge of each individual discharge line
• Tachometer
  -Displays engine speed in revolution per minute
  -gradual incr. in RPM for rated capacity indicated wear in the pump and possible need for repair
• Pumping Engine Coolant Temperature
  -displays the temperature of the coolant in the engine that powers the fire pump
• Pumping Engine Oil Pressure Indicator
  -shows adequate supply of oil being delivered to critical areas of engine that power the pump
• Pump Overheat Indicator
  -audible or visual indicator to warn that pump will overheat
• Voltmeter and Ammeters
  -Voltmeter- Provides battery condition
  -Ammeter- Indicates vehicle status of alternator and charging system
• Pump Pressure Indicator
  -commonly called discharge gauges
  -connected to outlet side of discharge valve so pressure being reported is pressure supplied to hose line
  -if the nozzle is shut down, pressure gauge for that discharge and master discharge will read the same
• Pumping Engine Throttle
  -Must be on pump panel
  -Used to increase and decrease engine speed (increase or decrease water pressure)
• Throttle knob (Vernier)- turn clockwise or counterclockwise to control pressure
• Automatic- Operated by throttle switch or push button to control pressure
• Primer Control
  -Used to operate priming device when pump will draft from static source
• Water Tank Indicator
  -Displays quantity of water held in water tank
• Auxiliary Cooling Devices
• Marine cooler- Inserted into hose in engine so coolant must travel through it as it circulates
• Immersion type cooler- Water in pump passes through a coil mounted in cooler

Question 26

Auxiliary Cooling Systems

Answer 26

• NFPA 1901 requires all pumping apparatus to have supplementary heat exchanger cooling system aka Auxiliary cooling system for the engine that drives the pump
• Primary function: control engine coolant temp during pumping
• Two types; Marine type, Immersion type
  -Both constructed so that water coolant does not contact engine coolant fluid in radiator so if can be used w/o contaminating engine coolant
  -Marine Type= small tubes similar to flues in steam boiler
  -Immersion Type= Coil or other type tubing, water passes through

Question 27

Flowmeter

Answer 27

NFPA allows flowmeters in place of pressure gauges on all discharges 1 ½ - 3” if larger can still have flowmeter but must also have gauge. Must provide readout in increments no larger than 10gpm