Abstract: A diaphragm valve assembly includes a valve housing having two or more fluid ports and defining both a valve chamber extending therebetween for fluid flow therethrough and an access port leading into the valve chamber. A bonnet covers the access port and defines an opening therein through which a valve stem arrangement extends. The valve stem arrangement includes a valve seat disposed within the valve chamber. The valve stem arrangement is slidable through the opening in the bonnet between a first position, wherein the valve seat is disposed in sealing engagement with a fluid port to thereby define a closed position of the valve assembly, and a second position, wherein the valve seat is disengaged from the first fluid port to thereby define an open position of the valve assembly. A diaphragm surrounds and is attached to the valve stem arrangement to form a seal therewith.