Pressure Drops When Sprinkler Zone Changes

I just installed a shallow well pump for irrigation. I live in Florida. I am down 25 feet and have a new 3/4 hp shallow well jet pump with a new 5 gallon pressure tank. I hooked it up to an existing irrigation system that had been on city water. The pump primed immediately and clean water immediately followed. I turned on the irrigation system and zone one worked perfectly as the pressure remained at about 25 psi. Then it changed to zone two (with fewer sprinkler heads). The pressure dropped to 10psi and the sprinkler heads just dribbled. Same with zone three. Then zone four worked perfect with all heads working and the pressure back up to 25. Zone one and four work about 80% of the time and have the low pressure problem about 20%. Zones two and three have low pressure 100% of the time. Even running the hose only, (thereby bypassing the valves) there is good pressure 80% and the low pressure problem 20% of the time. I am very confused. Any advice would be appreciated.

You must have different flow rates on your zones. In other words the zones use different amounts of water. The more water used, less pressure. Less water used, more pressure. The pump is going to pump the same no matter what zone you use. The problem is one zone gets along fine with the amount of water the pump gives and another zone needs more water than the pump can give. This can be either the pump is too small (or the wrong kind) or the well is not giving enough pressure.

If you were here in Hillsborough county, you would likely have 13 gallons per minute with your city water. A 3/4hp jet pump would just about run a zone that was designed for that amount of water. A 3/4hp self priming centrifugal would pump far more water than the 13 gallons used. However they are not to be used with a tank and pressure switch.

Did you do a pump test on this well to see how much water it will give?

bob...

Bob, No I did not do a pump test. However, I don't think the problem is the the flow rates for the zones for several reasons. First, the zones that work have the highest flow rates. Second, even when I block several sprinkler heads in the problem zones, the pressure does not increase. Third, I have the low pressure problem on the good zones occasionally, and finally... when I use only the hose and totally bypass the sprinkler system I usually get good pressure, however, occasionally I have the same low pressure problem. I called the pump manufacturer and they had no idea.

It's my opinion that it is not the pump. Pumps either pump good or they don't. The well could be having some sort of problem. Especially with the lack of rain we have had lately. The shallow wells in my area are all but dry.

bob...

The valves used in sprinkler systems are pilot operated valves that need a certain minimum pressure to operate reliably. Check the instructions for the valves.

We don't know your configuration, but if you are opening more than one valve in a zone, the first could be dropping the pressure enough to prevent the other from opening.

If you are trying to open valves on a zone befoe the others are fully closed, that could also be a problem.

Try making sure that the pressure in a zone is at least 20 psi before you try to open a valve, and then open them one at a time, and only one in a zone.

On some valves there is a screw to adjust the operating conditions or speed. If there is one on your valves, then check the instructions and try what it instructs.

zones

You are either trying to use more water than the pump can deliver to those zones, or the valves are not opening fully. But if the pressure is dropping the problem almost has to be the volume of water used by the heads. The pump doesn't know which zone is on, so it isn't going to produce less water just because it went from zone 1 to zone 2 or 3. And if the valve is not opening fully, thus reducing the output pressure, the pressure at the pump would increase because of the reduced demand.