What is friction loss and why is it important in pump calculations?

• A. Friction loss is water loss due to spillage.
• B. Friction loss is the pressure drop due to water moving through hoses and fittings; it must be offset by PDP to achieve target nozzle pressure.
• C. Friction loss is a measure of engine friction.
• D. Friction loss is the pump's inefficiency.

Answer: (B)

Friction loss is the pressure drop that occurs as water moves through hoses, fittings, and other appliances. It’s a hydraulic loss, not a loss of water volume, and it increases with higher flow, longer hose runs, smaller diameters, more bends, and elevation changes. In pump calculations you’re aiming for a specific nozzle pressure to deliver the desired stream. To reach that nozzle pressure, the pump discharge pressure must be high enough to overcome all the friction losses along the hose and attachments. That’s why friction loss is offset by the pump discharge pressure to achieve the target nozzle pressure.

Friction loss isn’t water spillage, nor is it engine friction or the pump’s internal inefficiency. Those other ideas refer to different kinds of losses. For example, if the nozzle needs 100 psi and the hose layout adds 50 psi of friction loss, you’d need about 150 psi at the pump discharge to get the nozzle at the desired 100 psi.