Fire Pump Hydraulics: Essential Formulas & Operations

Firefighting Pump Hydraulics: Essential Formulas & Calculations

This document outlines key formulas and operational guidelines for effective firefighting pump management and water delivery.

Pressure Calculations & Formulas

• Elevation Pressure (EP):
  • EP = 0.5 x height in feet
  • EP = 5 psi x (number of stories - 1)
• Head Pressure: Head Pressure = feet / 2.304
• Net Pump Discharge Pressure (Net PDP): Net PDP = PDP - Intake Reading
• Net Discharge Pressure (at Draft): Net DPD = PDP + Intake Pressure Correction
• Pressure Correction: Lift + Total Intake Hose Friction Loss ÷ 2.3
• Pump Discharge Pressure (PDP): PDP = Nozzle Pressure (NP) + Total Pressure Loss (TPL) (round to nearest 5 psi)
• Flow of Solid Stream: gpm = 29.7 x D² x √NP
• Nozzle Reaction (Solid Stream): NR = 1.57 x d² x NP
• Nozzle Reaction (Fog Stream): NR = 0.0505 x Q x √NP
• Percentage of Available Water: (Static - Residual) * 100 / Static

Hose & Flow Calculations

Hand Method (for 1.75” & 2.5” hose)

Details for the hand method are not provided in the original text, but this section is dedicated to it.

Condensed “Q” Formulas for Friction Loss

• 3” Hose Friction Loss per 100 ft: FL = Q²
• 4” Hose Friction Loss per 100 ft: FL = Q² / 5
• 5” Hose Friction Loss per 100 ft: FL = Q² / 15

GPM Flowing (All Hoses/Nozzles)

Subtract 10 from the first two numbers for flows greater than 160 gpm (This is a specific rule of thumb for GPM estimation).

Determining Total Pressure Loss (TPL) in Siamesed Hoselines (Equal Length) with FireCalc

1. Compute Friction Loss (FL) of the Attack Line (Do not include Siamese. Enter “0”).
2. Compute FL in the Siamese Lines (input #2 when asked if “Siamesed”).
3. Add FL from one Siamese hoseline, the attack line, and any applicable Elevation Pressure (EP).

Note: Add 10 psi for Siamese connections if flow is greater than 350 gpm.

Appliance Pressure Loss Guidelines

• 0 psi: For flows up to 350 gpm.
• 10 psi: For flows greater than 350 gpm.
• 25 psi: For all Master Stream Appliances.

Relaying & Drafting Operations

• Maintain Intake Pressure: 20-30 psi. Do not let it drop below this range.
• Maximum Vacuum a Pump Develops: 22 inches of Mercury.

Fire Department Connection (FDC) Guidelines

• Add 5 psi to Nozzle Pressure (NP) for each floor above the standpipe connection.
• Rule of Thumb: Pump 150 gpm into an FDC that has no information plate.
• Ensure at least two 2 ½-inch lines are connected.

Nozzle Pressure & Flow Specifications

• Handline Nozzle Pressure:
  • Fog: 100 psi
  • Solid Stream (SS): 50 psi
• Master Stream (MS) Nozzle Pressure:
  • Fog: 100 psi
  • Solid Stream (SS): 80 psi
• Low-Pressure Fog: 75 psi
• High-Pressure Fog: 800 psi @ 8-15 gpm
• Piercing Nozzle (3-6 ft): 100 gpm
• Chimney Nozzle: 100 psi @ 1.5-3 gpm
• Minimum Flow for Interior Firefighting: 95-100 gpm
• Maximum Flow for Handline: 350 gpm
• Fire Stream Practical Velocity: 60-120 feet per second

Pump Capacity Ratings (GPM)

• B (AA): >1500 GPM
• G (A): 1000-1499 GPM
• O (B): 500-999 GPM
• R: (Rating not specified)

Note: A pump receives its maximum flow rating at 150 psi.

Pump Operations: Series vs. Parallel

Series (Pressure) Operation

In series operation, the first impeller increases pressure and discharges 50-70% of the volume capacity to the second impeller, which increases pressure again. The total volume is limited to the amount that one impeller supplies.

• If the pump needs greater than 50% of its rated capacity, it should be set to parallel.
• Some manufacturers recommend remaining in series until up to 70% of required capacity.

Parallel (Volume) Operation

In parallel operation, each impeller delivers its rated pressure at 50% capacity for a sum of each stage. This supplies 100% of the rated volume at 150 psi at draft by using both impellers.

• It is always better to be in parallel for maximum volume.