How to choose a water pump for your application

How to choose a water pump for your application

Centrifugal pumps are commonly used for agricultural water pumping and may be driven by an electric motor or engine as appropriate. For example:
A water pump driven by an electric motor rated at 2HP( horsepower) delivers an average of 25,000-30,000   liters/hour
An engine-driven water pump using a petrol engine rated at 5-7HP( horsepower), or a diesel engine rated at 8-12HP ( horsepower), delivers an average of 20,000-50,000   liters/hour, depending on the throttle setting.

Pump sizing focuses on 2 aspects:
1. Water delivery quantity ( Q)  is the amount of water to be supplied each time. For example, if supplying 1 zones Q = 6 m³/hour
2. Water pressure ( H)  For a small, flat area with a main pipe no longer than 100 meters, the required water pressure is H = 25 meters

Where the main pipe is longer than normal, exceeding 100 meters, increase the standard pressure ( H=25) by 4 meters for every main-pipe length of 100 meters. For example, a main-pipe length of 300 meters
therefore requires water pressure ( H) = 25 + (4*300/100) = 25+12 = 37 meters. In sloping terrain, increase the standard pressure ( H=25) by the elevation difference between the area and the pump. For example,
the area rises by 5 meters, so the required water pressure ( H) = 25+5 = 30 meters

Note  
1. When selecting a pump, increase the water pressure ( H) by a further ~30% to compensate for pressure losses in the system ( Head Loss)
2. Motor power is measured in 2 forms: HP( horsepower) and Watt( watts) (where 1 HP = 750 W.)

Buying a pump  
1. Understand water requirements. For sprinklers, for example, know the required flow and pressure.
2. Choose a pump suited to the application: for example, a seawater/chemical pump for seawater or chemicals, , a centrifugal pump for agriculture, , sprinkler applications, , village water supply or firefighting, , and a submersible pump for groundwater, , clean water or wastewater.
3. Choose the pump size by checking whether it can provide enough water at the required pressure. For example:

• Water flow 280 liters/minute or 30 m3 / h ( cubic meters / hour)  
• Pressure 5 bar ( 10 m=1bar ) Delivery distance 50 meters equals 5 bar
• Motor size 220 V. or 380 V (Volt voltage supplied to the motor)  
• 50 Hz. (Hertz electrical frequency used by the motor)
• 400 W. (Watt electrical power used by the motor)  
• 1.6 A. ( Amp electrical current used by the motor)