standards / manuals / guidelines for small hydro development - AHEC

Spherical valves (for heads more than 120 m)Spherical valves have a body shaped like hollow sphere with flanges or otherconnection for mounting in a piping system.The rotor, shaped like ball, has a cylindrical hole through its centre at right angles tosupport shafts located on each side of valve. In open position with rotor opening parallel tothe flow direction, the valve offers an unrestricted flow with minimum disturbance to theflow path. To close the valve, the valve rotor is turned to 90 o from the axis of rotor opening.Spherical valve has tendency to close for positions less than 50% opening whichfacilitates emergency closing.Moveable seals reduce valve leakage when the valve is closed. Mostly valves haveboth upstream and downstream seal. The upstream seal is maintenance seal or emergencyseal, the down stream seal is working seal.When valve is closed under full pressure, the upstream maintenance seal allowsreplacement or maintenance of the working seal with out dewatering the penstock. Theupstream maintenance seals have positive mechanical locking to prevent accidental opening.• Daily checks of operating system and remedial measure are must.• Annual inspection and overhauling of mechanical seal after dewatering penstock ismust.• Annual inspection and over hauling of operating seal is also essential.• Annual overhauling of operating mechanism to ensure smoth working through outyear is also done.• Annual overhauling of the valve rotor and other parts are also taken up as required.Following Checks are also Essential• Checking and attending leakages from Valve & dismantling joint.• Checking and attending oil leakages from Servomotor• Checking the operation of operating valves.• Checking and attending the setting of Limit Switches & Operation of the same• Checking and attending leakages of distributing valve• Checking the correct working of the pressure gauges. Lubricate the parts if necessary.• Checking and attending for leakages in the piping.• Checking all the MIV System connections & Union for tightness• Checking all the MIV servo linkage during operation, looking for backlash• Cleaning of valve body, seal & solenoid valve• Checking the actuating solenoids for operation of valve. Cleaning the contacts androllers.• Checking the operation of bypass valve• Checking for cracks, pitting and cavitation etc. of MIV and Servomotor• Inspection of Rubber Seals• Checking trunions & bushes, bolts & nuts etc.• Checking gland packings and lubricationAHEC/MNRE/SHP Standards/ E&M Works – Guidelines for Operation and Maintenance of Small Hydropower Station 54