This custom high performance butterfly valve assembly operates normally as a modulating fail-close assembly. As recommended, a filter regulator is used on the input air to the positioner to keep air clean and prevent pressure spikes, helping to extend the life of the positioner. Using Max-Air’s PEX02 explosion proof positioner w/ external limit switches and a MT46.S4.F07-F10.CH22 spring return actuator, a 4-20mA signal modulates the valve as expected. However, by closing a 2-way ball valve and turning a 3-way T-port ball valve the inlet plumbing to the actuator is arranged in such a way that the positioner is bypassed and the open/close control is delegated to the auxiliary normal-closed 3-way solenoid valve. This allows a user to convert this modulating assembly to a simple open/close assembly and vice versa. In either mode the limit switches provide open/close feedback, regardless of whether the positioner is being used or not.