I'm trying to build a sprinkler system for my large yard. I've set up 2 zones each one with 8 heads being supplied by a 2HP well pump.
I'm using 1" pipe everywhere.
The first zone works fine and the well maintains about 70PSI; the second zone, which is about 20 yards longer than the first and also has 8 heads, works but the well pump is cycling.
I'm guessing that the problem is that with the longer line, I don't have enough pressure to push enough water through.
If I split the 2nd zone line into two with 4 heads on each line, would that work? Each line would be shorter but I'm not sure that would make any difference.
Any advice?
Best Answer
"Cycling" in a pressure system is generally when the pump is turning on and off too quickly. Pressure systems are specifically designed so that the pump runs up to its maximum pressure, then you use water from the pressure tank, until it reaches the minimum pressure, at which point the pump turns back on and runs until it reaches the maximum.
The recommended minimum run-time for a 1-2HP pump is usually 2 minutes. How you get to that is based on the flow rate of the pump, and the size of the tank.
Based on your 150gallon tank, and not knowing your flow (in gallons per minute, GPM), based on this tool here's some example flows/times:
As you can see, the higher the flow rate, the shorter the pump will run.
In your case, it sounds like one zone is basically matching the flow rate of the pump (you could verify this by watching the pressure gauge while it's running, it should be fairly steady). While this may reduce pump starts, if you use water elsewhere at the same time, your pressure will drop and the pump will not be able to keep the pressure as high.
Now, the flow rate the pump puts out depends on a couple things, most importantly: the pump itself (and now many stages it has), and the depth to the water level. Each submersible pump will have a chart showing the flow rates at different depths, so you'll need to find your model and the water level to figure this out. Here's an example though, using a 2HP pump I found while running at 60psi (depth to water: flow rate):
At first glance, this seems fine. My guess right now is that your first zone matches the flow rate of the pump, while the second zone is simply a lower flow rate than the pump. It's no problem, things are designed to work this way.
If you really want to reduce the cycling, you can hook up a bigger or a second pressure tank. This will give you more capacity, and so the pump will run longer, but it will also stay off longer while you use water stored in the tanks.
Now, if you had fast cycling (eg, <2 minutes run time) or "rapid cycling" (a couple seconds of runtime), then that would indicate a problem with the pressure tank. Normally the tank should be pre-pressurized at 2psi below your cut-off (low) pressure point - so in your case 43psi. To check this, you'll have to turn off your pump and let the water drain out (open a tap somewhere). You can top it up with a normal air compressor.