A pressure modulated flow control valve, particularly adapted for water irrigation applications, comprises an unitary elastomeric pin defining a flow passage therethrough, a sub-chamber formed entirely in the pin and communicating with an inlet to the valve, and a flexible diaphragm separating the sub-chamber from the flow passage. In operation, the diaphragm is exposed to water pressure prevalent in the sub-chamber to flex into and vary the size of the flow passage to control and modulate the flow rate therethrough. The interchangeable pin is mounted in a housing of the control valve to effect a preselected near constant flow rate through the flow passage.