Abstract: A reaming pin (70) is provided in a control orifice (34) by which pressure from a main chamber (26) is communicated to a control chamber (36) so as to provide force to hold a main valve member in the form of a flexible diaphragm (12) against a valve seat (14) and thus prevent fluid from flowing from the main chamber (26) to an outlet orifice (32). The control orifice (34) is displaced from the center of the diaphragm (12), but the reaming pin is so provided as to cause the variation in the lateral spacing between the pin (70) and the control-orifice walls to be less than it would be if the reaming pin were a straight, inflexible member rigidly mounted perpendicularly to the plane of the valve seat (14). In one version, the pin (70) is mounted on the diaphragm (12) itself and thus moves laterally with it. In another version, the pin (70') is pivotably mounted on the valve body so as to permit such motion.