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Hydraulic Information Charts

The following is basic hydraulic and pump operation information that should be known and understood by all firefighters. More specific and detailed information is learned while completing the Engineer Certification Process.

BASIC HYDRAULIC CALCULATIONS

The basic formula for determining engine pressure can be found below. Pump operators are taught to work this formula from the nozzle back to the pump.

Engine Pressure = Nozzle Pressure + Friction Loss + Plus or Minus Elevation

EP = NP + FL +/- E


NOZZLE PRESSURE

Depending on the type of nozzle and its intended use, there are four main nozzle pressures that must be considered. Achieving the correct nozzle pressure is essential to delivering the correct GPM.

Nozzle Pressures

  1. 1” and 1 ½” Fog Nozzles = 100 PSI
  2. 1 ½” Fog Nozzles used on 1 ¾” Hose = 75 PSI
  3. 2 ½” Fog and all Smooth Bore = 50 PSI
  4. Master Stream Devices = 80 PSI

FRICTION LOSS

Movement of water through fire hose causes a loss of energy. The amount of pressure developed by the pump and recorded on the discharge gauge will not be the pressure reaching the nozzle. This loss is referred to as friction loss. There are a number of equations used to determine friction loss. Friction loss is often recorded by 100’ of line, this is referred to as LL (length of Line)

Factors that influence Friction Loss

  1. The quantity of water being pumped
  2. The diameter of the hose
  3. The length of the hose
  4. The quality and age of the hose
  5. Appliances attached to the hose

ELEVATION

One of the laws of Physics states that a column of water 1 foot high exerts a pressure of .434 at its base. This number can be rounded up to .5, or ½ pound for every foot of rise. This results in a loss of pressure when moving water above the pump. Conversely, pressure will be increased for every foot of fall below the pump. This results in an increase in pressure.

Elevation Allowances

  1. In multi-Story buildings allow 5 PSI per floor. Excluding the first floor
  2. In uphill Wildland hose lays allow 5 PSI for every 10 foot gain in elevation
  3. In below grade or downhill operations decrease pressure by 5 PSI for each 10 foot increment below the pump

MASTER STREAMS AND RELAY PUMPING

Key Operational Points of Master Streams and Relay Pumping

  1. Deck Gun/Portable Monitor – 100 PSI to device plus friction loss in supply hose (must know GPM)
  2. Ladder Pipe – Determine inlet pressure for particular truck, plus friction loss in supply hose (must know GPM)
  3. Relay Pumping – 20 PSI positive inlet pressure plus friction loss in supply hose (must know GPM)

SMOOTH BORE NOZZLE FLOWS (GPM) AT 80 PSI

Tip Size 1 ¼” 1 3/8” 1 ½” 1 ¾” 2” Distributor
GPM 400 500 600 800 1000 450

 

FRICTION LOSS IN SYSTEMS AND APPLIANCES

Friction Loss Allowances

  1. Add 25 PSI for friction loss in standpipe systems
  2. Add 15 PSI for a Wye or Siamese when the flow is over 350 GPM

 SPRINKLER SYSTEMS

Key Operational Points of Sprinkler Systems

  1. Pump FDC at 100 PSI with no smoke showing
  2. Pump FDC at 150 PSI with smoke showing

HAND HELD HOSE LINE HYDRAULICS CHART

Each engine is equipped with a 2 sided laminated hydraulics chart. Pump operators should be familiar with this chart which is available to assist the operator in determining the appropriate pump pressure quickly.

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