Re: Bilge Pumps
Pumps are typically rated for output flow rate with two specified conditions: lift and head.
LIFT is the vertical distance a pump will raise water into its intake. For most centrifugal pumps lift is rated as zero. That is, the pump cannot lift water into its intake, and the pump must be immersed at the bottom of a sump so water flows to the pump intake by gravity.
HEAD is the vertical distance a pump can raise water on its outlet. The greater the head distance on a pump, the lower the pump output.
The diameter and design of the hose on a pump outlet will affect the output flow. Hoses with a corrugated inside diameter reduce flow. Of course, reducing the size of the hose reduces pump output.
The rating of most centrifugal pumps sold as "bilge pumps" is extremely optimistic and represents the optimum situation: zero lift and very minimal head. As you increase head the pump output will rapidly decline, until at some point it reaches zero if the head becomes too tall.
