Pipes and Cisterns: Inlets, Outlets and Negative Work

04 Try it yourself Interactive

Add the inlets, subtract the outlet

Pick a filling time for pipe A, optionally a second inlet B, and optionally an outlet. Each step converts one pipe into whole units an hour and the sign it carries. The last step divides the tank by the net rate — and if the outlet wins, the solver refuses to give a time and tells you why.

A fills in 8 h, outlet empties in 24 h

net +2 · fills in 12 h

Try pipe A at 12 hours with the outlet at 6. The drain is twice the inlet, so no amount of waiting fills that tank.

Press Next to work through it one step at a time.

Tank units–

Inflow / hr–

Outflow / hr–

Time to fill–

step 0 / 0