Abstract: An irrigation system having a valve assembly which is attachable to the underside of a sprinkler head is disclosed. The valve assembly includes a housing having interior walls which define an inner chamber, an inlet in fluid communication with the inner chamber, an outlet in fluid communication with the inner chamber and a valve seat surrounding the entrance of the outlet. The valve assembly further includes a flexible diaphragm which extends across the inner chamber and is attached to the interior walls of the housing so that it divides the inner chamber into an upper chamber and a lower chamber wherein the upper chamber is in fluid communication with the inlet and the outlet. The valve assembly further includes valve closing structure located in the upper chamber and attached to the diaphragm for opening and closing the valve to control fluid flow through the valve.