Question
My irrigation system is two years old.  It has three zones.  The system works fine on two zones, but I just noticed that the pump quick cycles (on, then off every 10 seconds or so) when the third zone kicks in.  FYI, this third zone is the largest zone coverage.  Any ideas why it works fine in two zones, but the last zone, 3, the pump quick cycles?

Answer
Hi Jennifer,

Thanks for your question.  I'll try to keep the "lingo" to a minimum...

Typically a pump operates in conjunction with a pressure switch.  When the working water pressure in a piping system falls below the preset limit, the switch turns the pump on.  Conversely when operating pressures exceed the upper limits, the switch will shut the pump off.  In this case, it appears the irrigation system was designed and installed without proper consideration of the operating limits and pressure settings of the pump and switch.  

To clarify, the pump cycles (turns off and on) during the operation of the third zone because the demand for water falls below the pump's operating window.  This window is defined as the upper and lower pressure limits set on the pressure switch mentioned above.  What "demand" means is how much water and pressure is required to operate the irrigation system properly.  When there's not enough demand for water from the irrigation system, the pump shuts off.  And when the demand for water increases, as your sprinklers continue to operate, the pump starts again.  An easy solution to pump cycling is to outfit the existing sprinklers on the third zone with larger nozzles or adding an extra head or two.  This will increase the demand and keep the pump operating for the duration of the third zone's irrigation cycle.  While this may be the easiest, it may not be the right solution.  The largest area of coverage does not necessarily mean the most water is required, which makes up the demand.  

You may try adjusting the lower limit of your pressure switch to a lower setting and adjusting the differential to a higher setting so that the operating window (mentioned above) covers a larger difference in pressure.  Remember - the lower limit turns the pump on and the upper limit shuts the pump off.  The difference between these pressure points is known as the differential setting.  If you're unsure how to proceed, call in an experienced pump or irrigation technician.

Let me know if this helps. I know it sounds complicated but it can be resolved once you grasp the concepts I've tried to explain.  

Good luck and let me know how you make out.

Regards,
Tony