Specifications Part 1 - Water Supply, Sewerage and Tube Well Works

6.3.8.3 The valve consists of a chamber carrying a floating ball which seals off theorifice when water rises in the chamber. The float is made of seasoned timbercore and provided with vulcanized cover for large opening chamber and arubber core in case of small ones.6.3.8.3.1 The vulcanized float sits under normal service condition against a valve seat ofmoulded rubber of special composition. The valve opens only when thepressure inside the pipe line reduces approximately to that of atmosphereduring filling or emptying out operations.6.3.8.3.2 The air accumulated at the highest points gets compressed and exertspressure on the rubber ball and causes it to depress throwing open the orificethrough which the accumulated air escapes.6.3.8.3.3 Air valves shall be installed on top of air valve tees. It should conform to IS14845:2000.6.4 Butterfly valves6.4.1 Butterfly valves are used to regulate stop the flow especially in large sizeconduits. They are sometimes cheaper than sluice valves for larger sizes andoccupy less space.6.4.2 Butterfly valves with no sliding parts have the advantages of ease of operation,compact size, reduced chamber or valves house and improved closing andretarding characteristics.6.4.3 These would involve slightly higher head loss than sluice valves and also arenot suitable for continuous throttling. The sealing is sometime not as effectiveas for sluice valves especially at high pressures.6.4.4 They also offer a fairly high resistance to flow even in fully open state becausethe thickness of the disc obstruct the flow even when it is rotated to fully openposition. Butterfly valves as well as sluice valves are not suited for operation inpartly open position as the gates and seatings would erode rapidly. Both typesrequire high torques to open them against high pressure, they often havegeared hand wheels or power driven actuator.6.4.5 Butterfly Valves with loose sealing ring are sometimes not effective, especiallyat higher pressures. Butterfly valves with fixed liner can overcome thisshortcoming, further the butterfly valves with fixed liner needs no frequentmaintenance for replacement of sealing ring as in the case of butterfly valveswith loose sealing ring.6.4.6 Valve shall be placed on a support of concrete so that non shear stress is inthe flanges. In case of axial thrust due to closure of a valves against pressurethe valve shall be anchored in the support in a suitable manner to transfer thethrust into the floor slab of the chamber.Urban Administration & Development Department Page 69