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The "Main pump", the one that you described in the beginning, can't lift more water from the well at the flow capacity beyond 32 liters per minute. For example, warmer water will decrease the suction lift capability of the pump. When selecting a pump it is important to get one with a SUBSTANTIAL MARGIN OF SAFETY for the NPSH requirement, because any little problem can cause it to fail. More horsepower will not solve the problem for that model of pump. That is enough pressure to operate most sprinkler heads.īut if the total demand of all of the sprinkler heads exceeds about 32 liters per minute, then none of them will work properly.īecause of the FLOW RATE LIMITATION OF THE PUMP, neither of the pumps will work for the number of heads that you have. The BG7 pump will deliver about 40 psi at that flow and the BG11 pump will deliver about 50 psi. You must limit the number of sprinkler heads so that they don't exceed the rated flow rate of the pump at the pressure for which the heads will operate. In other words, the pump can never pump more flow than the chart values for those values of lift. Those little tails on the chart labeled 8m, 7m, 6m, et cetera represent the limiting lift values corresponding to the flows, beyond which there is not enough Net Positive Suction Head (NPSH) to prevent cavitation in the pump. Based on the curves at the link you gave us, both of the pumps you mention are limited to about 32 liters per minute (about 7 US gallons per minute) at 7 meters lift.