A gas flow meter is a device that measures the volumetric flow of gas. Industrial gas flow meters can come in many forms and technologies and can be expensive and difficult to install. If an industrial gas meter is not available, an accurate gas flow meter can be made using water and a graduated cylinder. The theory behind this gas meter is that if there is a container full of water, as the gas is inserted into the container, it will displace a volume of gas per unit time. This volume of gas per unit time is the volumetric flow.
Fill the five-gallon bucket 3/4 full with water.
Connect one end of the plastic tubing to the tubing nozzle on the air tank. While holding the end of the plastic tubing, open the air tank valve allowing air to flow through the tubing. Slowly close the shut-off valve on the plastic tubing.
Place the graduated cylinder in the bucket of water and completely submerge it. It is important that all air is out of the cylinder. While still submerged, hold the cylinder upside down so that the opening is pointing to the bottom of the bucket.
Place the end of the plastic tubing under the water and into the graduated cylinder. The end of the tubing should be at the bottom of the graduated cylinder.
Open the shut-off valve and begin the stop watch. It is important to do these at the same time. Air will flow through the tubing and into the graduated cylinder. The air will push the water out of the cylinder at a rate equal to the gas flow rate.
Turn off the shut-off valve on the tubing and stop the stop watch at the same time. Without moving the graduated cylinder, observe the volume of water that was displaced by the air. Divide that value by the duration of time from the stopwatch and that is the volumetric flow rate of the gas. For instance, if the graduated cylinder indicated that 175ml of water was displaced over a course of 10 seconds, then the flow rate is 17.5ml per second.