Firefighting Hydraulics Basics

Basic Firefighting Hydraulics

• This manual provides general information about basic firefighting hydraulics.
• Each member must exercise appropriate control as dictated by rank for implementation.
• Hydraulics is the physical science of liquid properties at rest or in motion.
• A thorough understanding of basic hydraulic principles and water application is the foundation for efficient water supply and pumping operations.
• To create effective fire streams, pump operators need to know nozzle pressure, GPM flow, friction loss in the fire hose, friction loss in appliances, and pressure loss or gain from elevation changes.
• Pump operators should be able to perform "street math" at an emergency.
• Firefighters need to be aware of problems with the line (over/under-pressurized, burst length) through training.
• Over-pressurized lines lead to increased nozzle reaction, fatigue, increased air consumption, and reduced application rate by shutting down the line.
• Under-pressurized lines mean inadequate GPM, slower water velocity, and kink issues.
• Both scenarios with unsafe conditions for interior crews and confusion on the radio.
• Firefighters and drivers need to be familiar with nozzle type, target flow, and nozzle pressure.

Water Usage

• Water is the primary fire suppression agent because it is cheap, available, and supremely effective.
• A properly pressurized hose line with adequate GPM is the most useful tool.
• Weight is the physical property of water most important to firefighters.
• Incident commanders should be aware of the added weight of high-volume water application in defensive operations.
• Officers need to be aware of the weight of water when choosing attack lines.
• Water weight is directly proportional to the volume.

Volume Measurements

• 1 ¾” (1.88”) Firequip Combat Master Flow:
  • 19 lbs dry/uncharged per 50'
  • 7.21 gallons per 50'
  • 60.17 lbs water weight per 50'
  • ~80 lbs per 50' fully charged
  • 28.84 gallons static in a 200' charged 1 ¾” hose line
• 2 ½” Firequip Municipal Fire Hose, DJ 800, Nylon-Rubber-Lined, 2 ½” NST couplings:
  • 26 lbs dry/uncharged per 50'
  • 12.75 gallons per 50'
  • 106.4 lbs water weight per 50'
  • 132.4 lbs fully charged
  • 51 gallons static in a 200' charged 2 ½” hose line
• 3” Firequip Hydro Flow Small Diameter (SDH) Supply Line, 2 ½” NST couplings:
  • 33 lbs dry/uncharged per 50'
  • 18.36 gallons per 50'
  • 153.21 lbs water weight per 50'
  • 186.21 lbs fully charged
• Using 4 lengths of 3” to a gated wye (73.44 gallons) with 3 lengths of 1 ¾” (21.63 gallons) hose line will take 95.07 gallons of water to fill the supply and attack line.
• 5” LDH:
  • 105 lbs dry/uncharged per 100'
  • 102 gallons per 100'
  • 851 lbs water weight
  • 955 lbs charged

Hydraulics Terms

• Static Pressure: Pressure in a system or hose line with no water flowing.
• Residual Pressure: Amount of pressure left in the system while water is flowing.
• Gallons per Minute (GPM): Measures volume of flow from a hose line or pump.
• Gallons per Second (GPS): Measures water application in seconds, useful for visualizing impact of small amounts of water.
• Friction Loss (FL): The energy lost by water as it travels through a hose, measured by the difference between pump pressure and nozzle pressure via reading from discharge outlet to nozzle.
• With increased pump discharge pressure, the nozzle pressure increase is not equal to the engine pressure rise.
• More friction loss with more water being moved through the same size hose line.
• Less friction loss occurs with less water being moved through the same size hose line.
• Friction loss characteristics have changed with evolving hose technology.
• Overly conservative friction loss characteristics can lead to excessively high PDP, while optimistic estimations can inhibit efficiency.
• Internal PFD testing indicates Friction Loss per 50' of 1 ¾” (1.88”) hose line at 185 GPMs is 17 PSI.

Friction Loss Information

• Exact allowances cannot be made for friction loss due to variations in condition, design, manufacture, and age of fire hose, along with attached appliances.
• Determine FL by dismissing coefficients and following a precise process: removing internal Friction Loss from calculations for the hose line.
• Measure discharge pressure from the actual discharge, not just PDP, to determine FL in the hose line, it is impacted by plumbing and age of apparatus.
• To measure friction loss, place the 2 ½” in-line gauge from the high-rise kit on the discharge and the 1 ½” in-line gauge behind the nozzle and find the difference.
• In-line gauges help determine NP for smooth bore nozzles, pitot gauges are more accurate.

Nozzle

• Pitot gauges cannot be used on fog nozzles due to the broken stream, but in-line gauges can be used on smooth bore in the absence of pitot gauges.
• Pitot gauges are more accurate, regardless.
• Nozzle Reaction is based on Newton’s first law of motion: equal and opposite reaction based on water volume and pressure.
• Nozzle reaction is the backpressure that is being created in the last 3’ of line before the nozzle.
  • 1 firefighter can effectively handle 60 lbs of reaction force
  • 2 firefighters can effectively handle 75 lbs of reaction force
  • 3 firefighters needed to handle 95 lbs of reaction force
• Techniques, body mechanics, time on the job, and fitness can combat nozzle reaction.
• Target flow should match BTUs being produced, not fatigue the nozzle firefighter, and not create a kinked hose line or excessive whipping.
• Nozzle reaction management depends on staffing and nozzle type.

Target Flow and Pressure

• Target Flow is the GPM amount that a DPOP aims to achieve through proper Pump Discharge Pressure.
• PDP, also known as engine pressure, is the net result of hose calculations.
• PDP is calculated by adding Nozzle Pressure, Friction Loss, Appliance loss, and Elevation pressure.

Calculating Pump Pressure

• Determining Pump Pressure:

1. Desired nozzle pressure?
2. Target flow (GPM)?
3. Hose line diameter being deployed?
4. Friction loss per 50' length of the hose?
5. Elevation to consider (+5 PSI per floor)?
6. Appliances flowing greater than 350 GPM (+5 PSI)?
7. Standpipe, snorkel, tower ladder, ladder pipe or large manifold involved (+25 PSI)?

Fireground Tactics

• Target Flow, GPM, Friction Loss, and Nozzle Pressure are information a DPOP should have before arrival
• Length of the stretch and elevation will be situation specific.
• When operating with pre-connected hose lines, the information to achieve proper PDP should be established, except for elevation.
• Companies can have different target flows based on conditions
• Heavy fire in a tire shop = higher target flow based on fire load (230 GPM @ 100lbs NP)
• A 2 ½” hose line is always an option for occupancies and fire loads that demand higher GPMs to overcome the BTUs being produced.
• PDP has to be increased with a 1 ¾” hose line to overcome the increased FL created by the higher amount of GPMs being flowed.
• With higher flows through 1 ¾” lines, there is a ceiling far below the max capacity of a 2 ½” hose line.
• 2 ½” traditionally flows 265 GPM with 50lbs NP if operating with a 1 1/8” tip
• Aim a higher flow of 325 GPM with 50lbs NP and a 1 ¼” tip.
• Choosing the higher flow is viable, it places a larger divide between the max capacity of the 1 ¾” and the 2 ½”, but it does have a much higher nozzle reaction.

Equations

• Pump Discharge Pressure (PDP) = Nozzle Pressure + Friction Loss in the hose + Friction loss in Appliances + Pressure due to Elevation Changes.
• At a minimum, solve for NP + FL to determine the correct Pump Discharge Pressure.
• NP should be the first part of the formula to be solved for.
• PDP = NP + FL +AL + L +/- E
• PDP= engine pressure in pounds per square inch
• NP= nozzle pressure for the appliance used
• FL= total friction loss allowance in the hose line
• AL= friction created within an appliance other than standard nozzles or hose
• L= length
• E= elevation allowance

Tips and Pressure

• Hand held smooth bore tips:
• 7/8" = 160 Gallons Per Minute, 2.7 Gallons Per Second Rate, 60 Nozzle Reaction.
• 15/16" = 185 Gallons Per Minute, 3.1 Gallons Per Second Rate, 69 Nozzle Reaction.
• 1 1/8" = 265 Gallons Per Minute, 4.4 Gallons Per Second Rate, 99 Nozzle Reaction.
• 1 ½" = 325 Gallons Per Minute, 5.4 Gallons Per Second Rate, 123 Nozzle Reaction.