Evolution 7 — Relay Pumping Operation

Overview

Relay pumping extends water supply over long distances using multiple engines in series. In this evolution, the operator functions as the source pumper — receiving water from a hydrant and pushing it through a long hose lay to the attack pumper. The challenge is maintaining consistent pressure at the receiving end despite the significant friction loss in the relay line. A 1,000-foot LDH lay at 500 GPM creates substantial friction loss that the source pumper must overcome. If the source pumper under-pressures, the attack pumper starves. If the source pumper over-pressures, the hose may burst or the attack pumper's intake relief valve activates. Relay operations require coordination between two operators who cannot see each other.

Training Objective

Function as the source pumper in a relay operation, maintaining the required intake pressure at the attack pumper (typically 50 PSI) through a long-distance supply line. The operator must account for friction loss in the relay hose lay.

Skills Practiced

• Relay pumping principles and pump-to-pump coordination
• Long hose lay friction loss calculation for LDH
• Maintaining target pressure at the receiving end over distance
• Communication protocols in relay operations
• Pump-to-pump coordination without visual contact
• Pressure relief valve awareness
• Adjusting for changing demand at the attack pumper

Setup

Hydrant supply to the source pumper, which relays water through 1,000 feet of 5" LDH to the attack pumper. The friction loss over this distance at 500 GPM is significant. The operator must pump at a pressure high enough to deliver 50 PSI at the attack pumper's intake after accounting for all friction loss.

Scenario

A wildland-urban interface fire where the nearest hydrant is 1,000 feet from the fire. Two engines set up a relay to move water from the hydrant to the attack position. You are the source pumper operator. The attack pumper operator is relying on you to deliver consistent intake pressure so they can maintain their discharge lines. You cannot see the attack pumper — communication is by radio only.

What to Expect

The long hose lay creates significant friction loss. The operator must pump at a pressure high enough to deliver adequate intake pressure at the attack pumper after friction loss. The simulation monitors pressure at the receiving end and scores based on consistency. Pressure fluctuations at the source translate to larger fluctuations at the attack pumper due to the distance.

Tips

• Relay operations require higher pump pressures than direct attack — expect to pump at 150-200 PSI
• Communicate with the attack pumper operator about their intake pressure — they are your feedback loop
• Start at a moderate pressure and increase based on radio feedback from the attack pumper
• Watch for pressure relief valve activation if the attack pumper shuts down suddenly — your pressure will spike
• Friction loss in LDH is lower than smaller hose but still significant over 1,000 feet
• If the attack pumper requests more pressure, increase in 10 PSI increments and wait for feedback