Pump head (pressure)

There are four elements of the pump head:

  1.  The pressure needed for the drip emitter to operate.
  2.  The head loss (pressure/friction loss) across the entire system between the pump and the drip emitter.
  3.  Elevation lift over the piping network of the farm.
  4.  Suction lift to draw the water into the pump.

 

Working out your required pressure is simply a process of adding all of the above pressure head requirements. This provides your overall head requirement.

Head loss

Most irrigation components generate head loss.

Head loss could simply be called pressure loss, and some manufacturers call it friction loss. The head loss of a component is the amount of pressure (head) that is lost when water passes through it.

Why it matters

The very last dripper at the end of a block needs to have adequate pressure to perform. When designing your system, you need to calculate the head loss of every component to ensure that by the time the water reaches this dripper, there is still enough pressure.

The table below shows the total pressure required to operate an example drip irrigation system, calculated by each component of the total irrigation system.

  Head required
Component m feet psi
Emitter 9 30 13
Valve 2 7 3
Mainline 5 16 7
Elevation difference 5 16 7
Filtration 5 16 7
Suction 1 3 1
Miscellaneous 4 13 6
Total Dynamic Head 31 101 44
       

 

In the above example, you can see that the total head required to achieve 9 meters (13 psi) head at the drip emitter is 31 meters (44 psi).

Why do we care? Aside from the impact of how you design, remember that every extra bit of head is extra energy that is required.

Reading head loss
Head loss is expressed in a head loss chart or head loss table. The amount of head loss depends on the product and the flow rate (m3/h) (gpm). Below are two examples of head loss charts/tables, the chart being for a series of valves, and the table being of an automatic screen filter.

Product Head Loss Chart (bar)

Inlet/Outlet Flow Rate (m3/h)
15 25 50 75 100 150 200 300 400 500
inch mm Head Loss (bar)
3 80   0.02 0.07 0.15 0.25 0.43        
4 100     0.03 0.05 0.10 0.20 0.35 0.65    
6 150       0.03 0.05 0.10 0.18 0.33 0.68  
8 200         0.03 0.06 0.10 0.20 0.40 0.60
10 250           0.03 0.05 0.10 0.20 0.25
                       

 

Product Head Loss Chart (PSI)

Inlet/Outlet Flow Rate (gpm)
66 110 220 330 440 660 881 1321 1761 2201
inch mm Head Loss (PSI)
3 80   0.29 1.015 2.175 3.625 6.235        
4 100     0.435 0.725 1.45 2.9 5.075 9.425    
6 150       0.435 0.725 1.45 2.61 4.785 9.86  
8 200         0.435 0.87 1.45 2.9 5.8 8.7
10 250           0.435 0.725 1.45 2.9 3.625
                       

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