A leak detection system for detecting a leak within a duplex valve assembly is disclosed. The duplex valve assembly includes a first valve, a second valve and an intermediate fluid flow passageway fluidly interconnecting the first valve to the second valve. The leak detection system includes a means for indicating whether the first valve is maintained in a closed position or an open position, a means for indicating whether the second valve is maintained in a closed position or an open position, and a pressure change detector within the intermediate fluid flow passageway. The pressure change sensing means is at least partially positioned within the intermediate fluid flow passageway for detecting a pressure change within the intermediate fluid flow passageway.