irrigation valves for channels and for irrigation tanks are of three types . all are activated by a pair of tilting float arms to which a pair of floats are attached . one type is a t - shaped duct with a cylindrical valve disposed at 90 degrees to the part that is connected to the incoming flow . the floats rotate the valve . the second type has the same construction as the first type , thereby giving flow control but additionally has a rise and fall gate in the duct part that is connected to the incoming flow . the gate acts as a stop valve . the third type has a cylindrical duct connectable to the incoming flow but no valve and provides both flow control and stop valve facilities through a rise and fall gate actuated by the tilting of the float arms .