Question
Jim, I've reviewed most of the questions on this site but did not see one that addressed my issue. I have a 7 zone Rainbird sprinkler system. Zone 1 comes on without a problem but the pop-ups in zone 2 only partially come up with this zone starts. They spray some water while pulsating up and down. At the same time the anti-siphon valve starts banging and water flows from the bonnet.
The same thing happens when zone 3 starts but after a minute or so the pop-up's fully extend and the hammering goes away. The other 4 zones work fine. I'm leaning towards low water pressure as being the problem since I recently had an issue with Zone 1 coming on. The sprinklers would not pop up and only a little water would come out. I changed all of the spray nozzles to lower flow types and it fixed problem. My zone 2 and 3 contain the largest number of sprinklers. If low pressure is my problem, how can I improve the pressure?

Answer
Hey Shawn, it does sound as though you have low water pressure. A system can be designed, and still work good with low water pressure, and normally this has to do with the number of heads that are on each valve. Before getting in to this, I would be curious to know, where anti-syphon valve is installed. Is it installed on the main water line to the house, or is it installed off of a hose bib somewhere on the house? If it is not installed on the main water line, you can try moving it to the main water line, to increase your pressure(volume). If it is already installed off of the main water line,then you need to add more valves, and take off a few heads from the existing valves, and install them on the new valve. The first thing to determine how many heads you can put on one valve. A system is designed on GPM (gallons per minute). To determine how many gallons per minute the valve is putting out, go to your water meter, turn on the valve, and see how many gallons of water are used after one minute. Lets take an example that you are getting 10 gallons per minute(GPM). Each head uses x number of gallons per minute. You will have to get a chart from the manufacturer, to determine what nozzle puts out what GPM. For instance a Rainbird 12H (12 foot spacing,180 degree arc) might put out 2GPM. If you are getting 10GPM, then you could put 5- 12H heads on the line (5x 2GPM= 10GPM). What you need to determine is #1 how many GPM that you are getting from the valves, and #2 how many GPM each head is going to use. If you put to many heads on one valve, then you will not get them to pop up or spray right. I hope this gets you started in the right direction. Good luck and have a great day.