We are happy to Introduce you the micro type metal rotameter, which is very good for low flow rate measurement, the pipe is from 1/4" to 1".  It's really a good choice for your needs of measurement for flow flow rate water and air. 

Measuring Range       Water (20℃)                  1～3000 l/h

         Air（0.1013MPa 20℃）     0.5～90000 l/h

Measure Ratio                 10:1

Accuracy                     2.5%/4.0%

Working Pressure              PN16MPa

Medium Temperature             -40℃～+120℃ （Standard Type）

Ambient Temperature             -40℃～+80℃

Medium Viscocity                1/4” NPT, 3/8” NPT 1/2” NPT≤5mPa.s

                               3/4” NPT，1” NPT ≤250mPa.s

OUtput                       Standard Signal: 2 cables 4～20mA(24VDC power supply)

Power Supply                   24VDC±20%

Connection                     Side enter and out：1/4” NPT 

                               Down To Up：1/4” NPT, 3/8” NPT, 1/2” NPT，3/4” NPT，1” NPT inner Screw

Cable Entry                    M8×1 or as customer request

        Protection Class                  IP65

        Exd                        ExiaIICT3～6