5.3 Relay Pumping & Dual/Tandem Pumping Operations

5.3 Relay Pumping & Dual/Tandem Pumping Operations

When fireground water requirements exceed the capacity of a single apparatus or when the water source is located at a significant distance from the incident scene, driver/operators must implement specialized multi-pumper pumping configurations. Relay pumping, dual pumping, and tandem pumping represent advanced water supply tactics designed to overcome extreme friction loss, transport massive water volumes, or supply high-pressure discharge requirements. Executing these operations requires precise pressure management and strict adherence to safety protocols.

Relay Pumping Layout & Pumper Roles

A relay pumping operation employs two or more pumpers positioned at intervals along a supply line to move water over long distances from a supply source to the fire scene.

Component Pumpers & Responsibilities

1. Source Pumper: Positioned directly at the water supply source (hydrant or static draft location). The source pumper must be the apparatus with the largest pumping capacity available. Its primary responsibility is to draft or take hydrant water and pressurize the supply line to deliver water to the next pumper in the relay.
2. Relay Pumper (Inline Pumper): Positioned at calculated intervals along the hose lay between the source pumper and attack pumper. The relay pumper receives pressurized water at its intake, boosts the pressure to overcome downstream pipe/hose friction loss, and discharges it to the next pumper.
3. Attack Pumper: Positioned directly at the emergency scene. The attack pumper receives water from the relay line and supplies tactical attack lines, master streams, or fire protection systems.

Maintenance of Minimum Intake Residual Pressure

The cornerstone of safe relay pumping is maintaining a continuous positive intake pressure at every pumper in the relay chain.

• Mandatory Residual Limit: Every pumper in a relay operation must maintain a minimum intake residual pressure of 20 psi (140 kPa) at all times.
• Hydraulic Rationale:
  1. Prevents pump cavitation—a damaging phenomenon where low pressure causes water to vaporize into steam bubbles that collapse violently against pump impellers, causing severe metal pitting and sudden flow loss.
  2. Prevents atmospheric pressure from collapsing soft supply hose lines or damaging municipal distribution mains.
  3. Provides a essential safety margin against sudden pressure fluctuations caused by opening or closing attack handlines at the scene.
• Operator Adjustments: If intake residual pressure on a relay pumper drops toward 20 psi, the operator must immediately notify the upstream pumper to increase discharge pressure or request command to throttle back discharge streams.

Dual Pumping vs. Tandem Pumping Configurations

Driver/operators often confuse dual pumping and tandem pumping because both involve connecting two pumpers together. However, their mechanical connections, hydraulic goals, and operational configurations are fundamentally different.

Dual Pumping (Intake-to-Intake)

In dual pumping, two pumpers are connected intake-to-intake (or sharing a single high-capacity hydrant steamer port using a dual-intake connection).

• Configuration: Supply water enters the primary pumper's intake. A secondary intake hose connects an available intake port on the primary pumper to the intake of a second pumper.
• Objective: To utilize excess water volume from a high-capacity pressurized source. If a hydrant supplies 2,000 gpm at high pressure but the primary pumper only requires 750 gpm, the second pumper taps into the excess volume to supply additional attack lines or separate sectors.
• Key Characteristic: Operates in parallel; pumpers operate independently regarding discharge pressures.

Tandem Pumping (Discharge-to-Intake)

In tandem pumping, two pumpers are connected discharge-to-intake in series over short distances.

• Configuration: Hose connects the discharge of the first pumper directly into the intake of the second pumper.
• Objective: To achieve extremely high discharge pressures that exceed the maximum pressure capability of a single pumper.
• Tactical Application: Used primarily in high-rise building standpipe operations, long uphill supply lays, or high-pressure sprinkler systems where system working pressures must exceed 250 to 300 psi.
• Key Characteristic: Operates in series; pressures are cumulative.

High-Pressure Relay Precautions & Operational Safety

Relay and tandem operations involve significant hydraulic energy. Driver/operators must enforce strict safety measures to protect personnel and hose lines:

1. Pressure Relief Valves: All pumpers in a relay must have their intake relief valves set to open at 20 to 30 psi above their static intake pressure (typically set between 50 and 75 psi) to dump excess pressure surges caused by sudden handline shutdowns.
2. Discharge Pressure Limits: Unless using specialized high-pressure hose, standard supply line discharge pressures should not exceed 185 psi (for large-diameter hose) to prevent catastrophic hose failure and dangerous whipping actions.
3. Open vs. Closed Relays:
   • Closed Relay: Supply hose is connected directly from pumper discharge to pumper intake. Requires vigilant radio communication and intake relief valve protection.
   • Open Relay: Water is discharged into a portable folding tank at each relay pumper and drafted out. Eliminates pressure surges and water hammer, but requires additional setup time and portable tanks.
4. Communications Protocol: Always establish a dedicated relay radio talkgroup. Never shut down a discharge line or increase relay pressure without advising downstream pumpers.