A rising stem valve comprises a hollow valve body having a pair of ports defining a flow path through the valve body, a flange base through which one of the ports extends and a valve bonnet opposite the flange base. The valve includes a plunger/seal assembly able to be extended within the valve body to a first position for sealing the port in the flange base and to a second position for unsealing the port in the flange base. The valve also includes a locking mechanism for securing the plunger/seal assembly in the first position. The locking mechanism includes at least one cam lever attached to the valve body and a corresponding groove in a valve stem of the plunger/seal assembly.