Pump Operations
Drafting
Drafting is drawing water from a static source like a pond or tank that sits below the pump, using the pump to create a partial vacuum so atmospheric pressure pushes water up into it. It is how an engine pulls supply where there is no hydrant.
Because the source has no pressure of its own, the pump must first evacuate air from the suction hose. Atmospheric pressure then forces water up the lift to fill the pump. The achievable lift is capped by atmospheric pressure and falls with altitude.
A draft fails if air leaks back into the suction side faster than the primer can remove it. An unsealed connection or a bad gasket is the usual culprit, which is why drafting is as much about an airtight suction path as it is about the pump.
Where this shows up
Calculator
Drafting & Lift