Head pressure refers to the resistance that a pump must overcome in order to push water out of a pipe. The pipe that leads to a pond might lead back into it after passing through a filter system. It is important to consider efficiency when designing a pond pumping station. A higher efficiency pump will overcome less resistance to extract water from the pond through the filter system and through the waterfall. For the same amount of work, less resistance means more water will flow from the pipe.
Calculating and combining these elements will give you a total Head Pressure equivalent for your system, and can help you to choose the suitable pump.
Calculating Head Pressure
Head Pressure is calculated and shown in terms of feet (ft.) To figure out the total Head Pressure of your plan, you have to work out the difference in elevation between where the water is pumped from, to where the water is discharged.
Head pressure refers to the resistance that a pump must overcome in order to push water out of a pipe. The pipe that leads to a pond might lead back into it after passing through a filter system. It is important to consider efficiency when designing a pond pumping station. A higher efficiency pump will overcome less resistance to extract water from the pond through the filter system and through the waterfall. For the same amount of work, less resistance means more water will flow from the pipe.
This is a bit like driving on the highway. On steep hills, a car will slow down but still have the power to climb the hill. Similar to a pump, the pressure at the end of a pipe will cause it to slow down, which means less water is being pumped out.
A few factors can increase the pressure head in a pumping system. Head pressure is most noticeable when the stream or waterfall rises above the surface of a pond. If you have a waterfall that is 5 feet high, the system will instantly experience 5 feet more head pressure. Filters, fittings, and pipes are all other things that can increase head pressure. If the pipe diameter is too small for the flow rate, it can have a significant impact on head pressure.
The specs of a pump will indicate how many gallons per an hour it will pump at a given head pressure. A pump might produce 2000 gallons per hour at 2′ head. However, when the head is increased to 10′, which is more realistic for a water pond, the flow can drop to 1000 gph. It is important to know the head pressure of your pond system before you purchase a pump. It’s possible that a wrong-sized pump could be purchased if the head pressure is not taken into consideration.
Reference: http://www.thatpetplace.com/understanding-and-calculating-head-pressure-article