Q - I want use a suction pump to suck water from a water table 50 feet below the surface to irrigate my farmland at the rate of 200 gallons per minute. What type of surface pump do I use?
A - Strictly speaking, most pumps do not have "suction lift" capability, with the exception of vacuum pumps which have very limited application in vacuum service.
The "suction lift" capability of a pump comes from atmospheric pressure which "pushes" the liquid into the impeller which imparts energy to the liquid to pressurize and move it from one point to another. The "push" into the inlet of the pump comes about when the pump is "primed" to create a siphon effect when it starts to operate.
At sea level the atmospheric pressure is 14.7 PSIA which is equivalent to 34 feet column of water. Simply put, the atmosphere can push up a column of water 34 feet high under ideal conditions. Another way of saying it is that a pump can "suck" water from 34 feet below it under ideal conditions.
In reality, a pump can "suck" water at less than 34 feet below the ground because the atmospheric pressure is less than 14.7 PSIA at elevation above sea level. In addition, there are friction and hydraulic losses at the suction piping and suction nozzle of the pump. For these reasons, the practical "suction lift" capability of a pump is limited to [ * ] feet.
Since no pump can "suck" water beyond the practical limit of [ * ] feet below the ground, a surface pump will not work in this specific job. Only a vertical deepwell pump, submersible or lineshaft type, is suitable for this service.
[ * ] Some information are excluded in this article. Read more.