Head - See vertical lift and total dynamic head. Open Discharge - The filling of a water vessel that is not sealed to hold pressure. Pressure Tank - A fully enclosed tank with an air space inside. As water is forced in, the air compresses. The stored water may be released after the pump has stopped.
Most pressure tanks contain a rubber bladder to capture the air.
Pressure Tank Precharge - The pressure of compressed air stored in a captive air pressure tank. If precharge is not set properly, the tank will not work to full capacity, and the pump will cycle on and off more frequently. Copyright 1996 by Dankoff Solar Products, Inc.