Relay and Dual Pumping Operations
Relay pumping
A relay is a series operation: a source pumper discharges through hose to a relay pumper, which boosts pressure to the next pumper or the fireground. Relay pumpers should maintain an intake pressure in the range recommended by the pump manufacturer and department practice, commonly about 20 to 50 psi, to avoid cavitation and hose damage. Use large-diameter hose to reduce friction loss, position apparatus for access and safety, and set relief valves to protect against pressure spikes. Communicate before changing pressure or flow.
Dual pumping
Dual pumping uses two pumpers in parallel from the same source, or into a common manifold, to increase total flow rather than pressure. Match discharge pressures, use check valves where required, and prevent one pumper from backfeeding the other. A dual-pumping setup can supply more volume than either pumper alone, but only if the source and manifold can support it.
Worked example
A relay moves 1,000 gpm through 1,000 feet of 5-inch hose. Using FL = C x Q² x L with C = 0.08, Q in hundreds of gpm, and L in hundreds of feet: FL = 0.08 x 10² x 10 = 80 psi. If the receiving pumper needs 30 psi intake, the source pumper must produce 30 + 80 = 110 psi at its discharge, plus elevation. Reasoning: a source pressure of 150 psi would give 70 psi intake, which may be too high and should be reduced or managed.
Traps
Do not confuse series relay with parallel dual pumping. Do not relay through small hose without calculating loss. Do not change pump pressure without radio notice. Do not let a relay pumper run without a relief valve or intake pressure limit.