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

with the main. For large aqueduct pipe line, a triple orifice air valve is availablewith two large orifices and one small orifice.6.3.4 For high pressure, stainless steel floats are used instead of vulcanite-coveredballs. In case of high velocity air discharge, special design of air valves are alsoavailable. Under such situation if usual type of air valves are used there isdanger that the ball might be carried to its seat by the air stream before theaccumulated air has been completely exhausted.6.3.5 Single air valves of small sizes are provided with stop cock or peet valves withthe inlet of the air valve, whereas double air valves are provided with astandard sluice valve fixed, with inlet flange of the air valve or with integralvalve, Regular maintenance at least on annual basis in necessary to ensurethat the balls are free to move and that the seat do not leak. In very coldweather it is necessary to drain the chamber of valves to avoid any damagedue to frost.6.3.6 Construction of water tight chamber around the air valve when fixed in street isnecessary to avoid the admission of any polluted water.6.3.7 The pressure ratings for single air valve and double air valve are as mentionedbelow :Table No.6.4Type of valveMax working pressure,bar gaugeHydrostatic testpressure in bargaugeShell Seata). Single Air Valve (screwed)-10- -516 10b) Double air valve (flange faced)(size 40 to 200 mm)-1016 10c) Kinetic air valve (size 80 to 200 mm) 10 16 10Note : 1 Bar = 0.9869 atm and1 atmosphere = 1.000 kg/cm²= 14.22 PSI6.3.8 Kinetic Air Valve:6.3.8.1 When ordinary single air valve is used, the air or water from the rising main isadmitted in the ball chamber of the air valves from one side of the ball. Thisarrangement has disadvantage, i.e. once the ball goes up, it does not comedown even when the air accumulates in the ball chamber and also due to theair rushing in, it stirs the ball making it stick to the upper opening which doesnot fall down unless the water pressure in the main drops down.6.3.8.2 The kinetic air valve overcomes these problems because the air or waterenters from the bottom side of the ball and the rushing around the ball exertsthe pressure and loosens the contact with the top opening and makes the ballto drop down.Urban Administration & Development Department Page 68