What is the primary difference between a supply line and an attack line, and how does it affect pump discharge pressure settings?

What is the primary difference between a supply line and an attack line, and how does it affect pump discharge pressure settings?

• A. Attack line carries water from source to pump and supply line goes to the nozzle.
• B. Supply line feeds the nozzle directly, bypassing the pump.
• C. Supply line brings water from source to pump; attack line carries water from pump to nozzle, and each has different friction losses requiring appropriate discharge pressure.
• D. Supply line reduces friction losses; attack line has none.

Answer: (C)

The key idea is how water travels and where losses happen. The supply line brings water from the water source (like a hydrant) to the pump, while the attack line carries water from the pump to the nozzle. Each path has friction losses that depend on hose length, diameter, fittings, and elevation. Because the nozzle needs a certain operating pressure, the pump discharge pressure must be set high enough to overcome the friction losses in the attack line so the nozzle actually receives the required pressure. The supply line friction affects how much pressure the pump can develop from the source, but the nozzle pressure is determined by the attack line’s losses and any elevation differences. That’s why this option correctly describes the roles and why appropriate discharge pressure is needed to account for the different friction losses along each line. The other descriptions mix up the flow paths or ignore that both lines experience friction losses.

The key idea is how water travels and where losses happen. The supply line brings water from the water source (like a hydrant) to the pump, while the attack line carries water from the pump to the nozzle. Each path has friction losses that depend on hose length, diameter, fittings, and elevation. Because the nozzle needs a certain operating pressure, the pump discharge pressure must be set high enough to overcome the friction losses in the attack line so the nozzle actually receives the required pressure. The supply line friction affects how much pressure the pump can develop from the source, but the nozzle pressure is determined by the attack line’s losses and any elevation differences. That’s why this option correctly describes the roles and why appropriate discharge pressure is needed to account for the different friction losses along each line. The other descriptions mix up the flow paths or ignore that both lines experience friction losses.