How do you compute acceleration head in a vertical lift suction line and why does it matter for pump suction?

• A. h_a = (L/g) (dV/dt); accounts for inertial effects of accelerating the fluid column; affects available suction head and pump performance during transients.
• B. h_a = g/L (dV/dt); accounts for viscous effects of the fluid; affects energy losses.
• C. h_a = V^2/(2g); represents dynamic head due to velocity.
• D. h_a = μ V /(ρ g); represents viscous losses in the column.

Answer: (A)

The essential idea is that when the pump flow changes, the column of liquid in the suction line has inertia and must be accelerated or decelerated. In a vertical lift, the length of that liquid column matters because more mass needs to be accelerated, which creates an additional head that the pump must overcome during transients. This inertial effect is captured by the acceleration head, given by h_a = (L/g) times the rate of change of velocity, dV/dt. Here L is the length of the suction column, g is gravity, and V is the fluid velocity in the suction pipe.

If the pipe area is constant, V = Q/A, so dV/dt = (1/A) dQ/dt, and h_a = (L/gA) dQ/dt. This shows that rapid changes in flow (large dQ/dt) or longer suction legs (large L) produce a larger acceleration head, which reduces the net suction head available to the pump during transients and can push the suction pressure toward cavitation if not managed.

Steady-state operation with no change in flow makes dV/dt nearly zero, so the acceleration head is negligible. The other expressions describe velocity head or viscous losses and do not represent the inertial effect of accelerating the fluid column in the suction line.