Cylindrical Pipes Cylindrical drip irrigation pipes are multi season pipes. Available with 16- and 20-mm diameter. Flow rates available are 2, 4, and 8 LPH for 16 mm pipes while 2 and 4 LPH are available for 20 mm diameter pipes. In addition, drip irrigation pipes produced with different wall thicknesses. Flow at different pressure values Code 16 mm Cylindrical Pipe Flow Curve 20 mm Cylindrical Pipe Flow Curve