Question
A couple of my sprinkler valves have stopped working. They are loud when activated and produce a small amount of flow. If I swap the solenoid with the neighboring valve (that works) it behaves the same. I've also replace the diaphragm. These are the irritrol valves with the metal rings. Thanks for your time in responding.

Answer
Try adjusting the low control.  There should be a knob or other device on top of the valve that adjusts the flow.  To adjust it, open it all the way (counterclockwise), then close it all the way, counting the number of turns.  Then open it back up halfway.  This is the proper adjustment.