Question
Mr. Welch, I apologize in advance for the lengthy email, but wanted to give you all the information I could.
I noticed this problem after seeing some weeping at one of the Valve #1 sprinker heads at the lowest point of the yard (several hours after programmed to turn off), then discovered the RainDial 600 controller display flashing the time on/off.  I attempted to set the controller to run sprinkler zones 1 & 2 separately; the display flashed twice and then went blank with no valves opening.  After repeated attempts with the same result, I reset the breaker and reprogrammed the controller - but again, same results.  I then remembered to replace the 9v backup battery, which has at least stopped the display from flashing.  
When programmed, Valve 1 will open and has sufficient pressure to operate all 5 sprinkler heads (despite the loud & rapid clicking).
When programmed, Valve 2 will not generate enough pressure to raise any of the heads in its zone.  With this valve only, I also hear a rattling noise in the ground approximately 12 feet away, (sounds like the PVC line that leads to the heads in zone 2).  With Valve 2, after unscrewing the bleeder, the heads will all rise and operate fine, but within 4 seconds after closing the bleeder screw, the heads will collapse; after this, there is water visibly coming from the heads -- significantly more than just weeping.
I also have a 3rd valve on the same controller that operates a drip system; it also has the same loud clicking noise, but seems to produce enough pressure to water adequately.
When manually opening all valves in the valve box, there is NO loud clicking noise; all heads in both zones operate perfectly, even with both valves open simultaneously, verifying sufficient water pressure from the supply line.
I have inspected the interior of each valve for calcium build-up (as someone suggested in a previous post for a similar issue) and found none.  I have also removed and inspected each solenoid, but see nothing out of the ordinary.
The controller is approximately 7 years old and up to this point, has worked perfectly.
I am doubting that the solenoids are faulty, as it doesn't make sense for all three to fail at the same time.
The solenoids for each valve are labeled:
811 SOLENOID
24V  60Hz
Inrush Amps  .4
Holding Amps  .2

With a volt meter I have confirmed 27 VAC at the controller input, but when programmed to come on, the output voltage going to each valve is only ranging from 11.2 - 14.4.  Would this be the problem ?  And if so, is there a solution other than replacing the controller ?

I greatly appreciate any suggestions you may have.

Doug


Answer
Thanks for your question. No need apologize for the length of you question, the more info the better.
The last paragraph is the most important. The valves need a minimum of 20 volts to work properly. Try removing the "COM" wire and test again. If the voltage is still low then the controller is probably  bad. If the voltage is correct, then you should be checking the field wiring. If you want to try another test. Remove the 2 wires from the transformer and connect them directly to the "COM" and "ZONE 2" wires. If this make the valve open, then it's definitely the controller.
The rattling noise you hear is the valve partially opening then closing rapidly. It referred to as "water hammer". A good indicator of low voltage to the valve.
Hope this helps.

Matt