When pumping 20 ft below the pump, what adjustment is applied?

When pumping 20 ft below the pump, what adjustment is applied?

• A. Add 5 psi per floor
• B. Subtract 5 psi per floor
• C. Subtract 10 psi per 20 ft
• D. Add 10 psi per 20 ft

Answer: (C)

The key idea is hydrostatic pressure from the water column on the suction side. When the suction is below the pump, the water at the intake is under additional pressure due to depth, so the pump doesn’t have to generate as much discharge pressure to reach the same nozzle pressure. In standard firefighter practice, that hydrostatic head is about 10 psi for every 20 ft of vertical difference. So pumping from 20 ft below the pump means you subtract 10 psi from your discharge pressure to account for that extra suction pressure. If the suction were above the pump, you’d generally add pressure instead.

The key idea is hydrostatic pressure from the water column on the suction side. When the suction is below the pump, the water at the intake is under additional pressure due to depth, so the pump doesn’t have to generate as much discharge pressure to reach the same nozzle pressure. In standard firefighter practice, that hydrostatic head is about 10 psi for every 20 ft of vertical difference. So pumping from 20 ft below the pump means you subtract 10 psi from your discharge pressure to account for that extra suction pressure. If the suction were above the pump, you’d generally add pressure instead.