Coralville Fire Department November 2006 Training Basic Fire Pump Theory and Operation Instructor Lee Lautzenheiser

Coralville Fire Department

November 2006 Training

Basic Fire Pump Theory and Operation

Instructor Lee Lautzenheiser

Pump Theory & Operation

Our goal today is to provide you with some basic information regarding fire pumps and

friction loss. With this information you should have a better understanding of the

way pumps work and how to properly operate the pumps on the apparatus.

After this presentation we will go through actual pumping exercises.

Pump Theory

• Centrifugal Pumps

– Single-Stage (71)

– Two-Stage (other pump apparatus)

Pump Theory

• Single-Stage

– No Transfer Switch for Pressure and Volume Modes

– Limited to 2000gpm

– Simpler than Two-Stage Pumps

Pump Theory

• Single-Stage Diagram

Pump Theory

• Single-Stage Diagram

Pump Theory

• Two-Stage

– Two modes: Pressure & Volume

– Pump has two impellers vs. single

– Larger pump capacities (both volume & pressure) are available

Pump Theory

• Two-Stage

– In volume mode the impellers are in parallel which gives more water volume but require higher RPMs for a given pressure

– In pressure mode the impellers are in series which gives higher water pressure at a lower RPM but less total volume is available


• Two-Stage

– Switch to volume mode when you are using 50-65% of the pumps rated volume

– To transfer between modes the engine RPMs must be less than 1000 and the output pressure under 100psi


• Two Stage

– Coordinate transfer with crews as operations will be briefly interrupted

– Anticipate pressure changes when changing modes:

• Volume Mode will require higher RPMs• Pressure Mode will require lower RPMs

Pump Theory

• Two-Stage Diagram

Pump Theory


– Operates by “slinging” the water out of the pump outlet

– Little to no damage occurs when lines are shut down (remember WATER HAMMER)

– When no water is being discharged though the pump will heat the water from the friction



– Recirculating water is a must to prevent overheating when no water is being flowed

• Pumping off the tank – crack open tank fill valve• Pumping off a hydrant –crack open a discharge

using a small hose to redirect water to an “out of the way” location

• Pumping off a draft – crack open a discharge and flow water back into the water supply



– Pressure Relief Valves

• Set about 20psi above desired discharge pressure

• Do not operate partially opened as it will not suppress the pressure surge

• 71 does not have a pressure relief valve but computer governor that automatically throttles back when there is a pressure surge



– External Pressure Relief Valves

• All trucks except 71 have a relief valve on the 5” intake adapter which are set at 100psi

• When pumping to other apparatus use a discharge pressure of 60-80psi to mimic hydrant pressure

• Expect the discharge pressure to change when going from tank to hydrant or visa versa



– Draining Pumps

• Open all drains

• Open all intakes and discharges except the tank suction



– Require priming when drained and this may even be necessary when operating off the tank

– Also priming is needed for drafting and water needs to remain flowing to keep the prime

– May use another hose or deck gun to flow water into the water supply


• Primer Pumps

– Primer pumps are positive displacement

– You do not “suck” water but rather the primer pump reduces the pressure in the pump by evacuating the air or water and then the outside air pressure pushes water into the pump



– Standpipe Operation

• Pump at marked pressure or if not marked then 150psi

• Add 5psi for each floor

Pump Theory

• Friction Loss

– As water moves through the hose it will encounter friction

– Theoretical Formula

• FL = CQ2L where C = coefficient for a typical hose of a given size, Q = flow/100, and L = length/100

Pump Theory

• Friction Loss

– For our preconnects we have 200 feet of 1¾” hose with a 125gpm at 75psi nozzle…

• FL = (15.5)(125/100)2(200/100)• FL = 48.4psi

– Total PSI needed is 75psi plus 48.4psi or 123.4psi

Pump Theory

• Friction Loss

– For 200 feet of 2½” hose with a 250gpm at 100psi nozzle

• FL = (2)(250/100)2(200/100)• FL = 25psi

– Total PSI needed is 100psi plus 25psi or 125psi


• Friction Loss

– This is why we pump preconnects at 120psi


• A few other pointers…

• Add 5psi for each 10 feet of elevation

• Typical master stream fog nozzles operate at 80psi, smooth bore nozzles at 50psi and handheld fog nozzles at 100psi

• Never let the intake pressure drop below 20psi when operating from a hydrant as damage to the water system may occur

Pump Theory & Operations

• Remember that if you get hung up to stop and think about what is going on. Start over from the beginning if necessary.

• Get out and practice, no need to actually take a truck out as you can verbally go out to the trucks and walk through it

Pump Theory & Operations

Questions?

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Coralville Fire Department November 2006 Training Basic Fire Pump Theory and Operation Instructor Lee Lautzenheiser