Clogged line
There could be a clog in the lines feeding some of the sprinklers, or clogged up sprinkler heads.
- Remove all the sprinkler heads (the procedure will vary based on the type of heads).
- Inspect and clean the heads.
- Turn the system on.
If you don't notice any dirt or gunk coming out, and the pressure does not increase in the low flowing outlets. Cap the working outlets, and turn the system back on. If you still don't notice a difference, you might have to dig up the lines to inspect them.
Damaged line
The line feeding some of the sprinklers could have been crushed, damaged, or broken.
- Cap the working sprinklers.
- Turn the system on.
If the pressure in the low flow heads does not increase, you'll likely have to dig up the lines and inspect them.
Not enough pressure
It could just be that the system does not have enough pressure for all the heads to work simultaneously.
- Cap one of the working sprinklers.
- Turn on the system.
- Repeat.
If each time you cap an outlet you notice the pressure increase in the low flow heads, it could be that there is just not enough pressure to operate all the heads at once. In this case you might have to have the system split into zones, and only run one zone at a time.
First we need a Manufacturer and possibly if you can find it, a model number. Irrigation control valves like this have two parts, a diaphragm operated water control valve and a vacuum breaker. Typical Rainbird system shown here.
The control valve uses an electrically controlled needle valve that operates the main diaphram valve through servo action (small force controls large force). Cross section to give an idea how this works. When the needle is seated, full water pressure operates on the upper side of the diaphragm, shutting water flow off. When the needle opens, the pinhole in the diaphragm is smaller than the needle opening, pressure dumps and the diaphragm opens.
Where your leak is occurring is in the vacuum breaker (right hand side below). This device operates to prevent water siphoning back into the water line through the control valve if water pressure drops. It is essentially a check valve with one side open to the atmosphere that closes under pressure and if the parts are damaged through wear, foreign object stuck in the seat, corroded in place, etc. becomes as you've found, a large volume leak under pressure.
This is where having all that manufacturing information is important as most of these can be repaired if you can find the repair kits. Otherwise, it's complete replacement time.
Exploded diagram of the above example Rainbird unit less the solenoid control.
Champion Classic Brass 3/4" Automatic Actuator and Anti-Siphon with Union
Manufacturer is Arrowhead-Champion http://www.championirrigation.com
I've used Irrigation Direct for other product, their replacement parts page. There are other businesses listed. If you have a large irrigation supply anywhere near, they probably carry the product. Arrowhead is a well known manufacturer of brass plumbing fittings.
The Champion product has been around in manual systems since the 1930's. To get the Vacuum Breaker loose, you might need gentle heat on the body. Keep it on the breaker side.
Breakdown of the original Manual Valve and Anti-Siphon with Union
And the bits in the Anti-Siphon Valve that are giving you grief
Best Answer
This usually comes after years of use where there is grit in the water. The plastic sliding surfaces get abraded and start to stick. Usually the result is that you have to replace the sprinkler as the tube and piston are both pretty well shot.
You might try unscrewing that black cap, the insides come out and with removing the spray head at the top, you can completely disassemble all the sliding parts. Flush the cup underneath the cap out to remove sediment and touch up all the sliding surfaces with paste wax after completely cleaning them.
Which brings up mineral fouling, if your water has mineral content, soak everything in white vinegar to help the crusts disappear and clean out the filters.
If the wax doesn't add some plasticy glidiness back after reassembly, then replacement is the only option left.
Often irrigation supplies have the filters and nozzels available by the box load, optionally, the internals. Usually, you end up buying the whole shebang, if you stick with only one brand and don't have to deal with freezing, unscrew the top, leave the cup in the ground and replace just the working parts. Acceptable for DIY, professionals don't have time to waste on this and just replace them.
Down on the ranch, we called it
Irritationand it involved moving tarp sticks in ditches and 20' RainBird pipes. At least it didn't have the added misery of suburban irrigation that can be totally halted by fine sediment. Oh, the misery of Drip!Note: this appears to be a simple spray assembly, if you have rotators, the water motor and other parts are usually getting near life's end when this starts happening so attempting the wax job just postpones the inevitable.