2.3 Selection of Inlet/Outlet Valve

2.3.1

The turbine inlet valve shall be selected through techni cal and economic comparisons on the basis of head,diameter and following conditions.If the inlet valve is not provided,other runaway prevention measures shall be taken.

1 In the case that two or more turbines are fed by one penstock,every branch pipe shall be provided with an inlet valve.

2 For one short penstock for one unit,the inlet valve should not be installed.For one penstock for one unit on a sediment-laden river or one long penstock for one unit,technical and economic comparisons shall be made to justify the rationality of installing inlet valve or cylindrical valve.

3 For the low head and unit water conveyance system of the run-of-river hydropower plant or hydropower plant in river channel,inlet valve shall not be installed.

2.3.2

Under the worst condition or the maximum flow,the turbine inlet valve shall be able to shut down in the dynamic flow.The turn-off time of the valve shall not exceed the allowable time of the continuous unit operation at maximum runaway speed.The inlet valve shall be able to open smoothly without severe vibration when the differential pressure on both sides of the valve does not exceed 30%of the maximum hydrostatic pressure.

2.3.3

The outlet valve should not be installed in the case of the low-head vertical axial flow pumping station,horizontal tubular pumping station,inclined axial flow pumping station and the vertical mixed flow pumping station,but other reliable measures for stopping the flow shall be taken to prevent the unit from runaway in the case of sudden power off.The flow stopping measures shall be determined by the technical and economic comparisons based on such factors as the water level variation range of the outlet pool,pumping station head and characteristics of the unit,etc.and matched up with the type of the outlet passage.The flow stopping measures shall meet the following requirements:

1 Reliable operation.

2 Simple equipment and flexible operation.

3 Convenient maintenance.

4 Little influence on the unit efficiency.

2.3.4

The bulkhead valves shall be installed on the inlet pipe and behind the outlet service valve of each pump.

2.3.5

The outlet service valve of pump shall be able to shut down in the dynamic flow.The rigidity and strength of the valve shall meet the requirements for possible hammer pressure rise,reverse rotation speed rise,and reverse rotation time due to the pump-motor sudden outage.The hydraulic operate valve with two steps closing device or multi-function hydraulic control valve should be applied as the service valve.

2.3.6

For a hydropower plant or a pumping station with the maximum head of 250m and below,the hydraulic control butterfly valve should be applied as the service valve or bulkhead valve.For a hydropower plant or a pumping station with the maximum head above 250m,the hydraulic control spherical valve should be applied as the service valve or bulkhead valve.