The inlet valve is installed at the end of the penstock or at the inlet of the turbine. It is classified into several types as butterfly type, spherical type, sluice type and needle type. The inlet valve reduces the interrupting time for passing the water during the turbine check or dismantlement and also remains the operation of the other turbines in case of using the same penstock. The inlet valve will also reduce the water leakage from the turbine. Moreover, it will keep the turbine safe from the damage when it has to be stopped from the loss of governor pressure of the oil system or other defections. The inlet valve must be designed to be large enough to stop the maximum flow of the water through the turbine. However, the construction cost of the inlet valve is quite expensive and some types of the inlet valve cause the head lost when the engine is operated.