Question
when one zone is opened there is continuous thumping in the valve and heads appear to have air. This disappears when the Richdel bleeding screw is opened and closed.Re-occurs again when zone is started.Have tried continually bleeding the line. The circuit is very level.Thks

Answer
Hey Ken, if the valve works fine when you open the bleed screw, but not when the controller turns it on, then either the diaphragm is worn out and needs to be replaced, or the hole that is in the middle of the solenoid port is clogged up. To un- clog  the port, turn the water off, and unscrew the solenoid, now simply put a needle through the hole, and make sure there is nothing in the hole. Turn the water back on before you screw the solenoid back on, and make sure you have a steady stream of water coming through the hole. Turn the water back off, and screw the solenoid back on. To Replace the diaphragm, you will need to unscrew the screws to access the diaphragm. Go to www.irrigationtutorials.com, and this website will show you how to replace the diaphragm. Good luck and have a great day.