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This page contains calibration tables as well as other supporting information for users of MATHESON Rotameters.
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Take the reading from the middle of the ball.
Read the top ball until it goes above the top of the chart, then read the lower ball. (The black ball is glass and the silver ball is stainless steel)
The flow range of the tube is extended with two ball floats instead of one.
The 0-150 scale is in millimeters. Calibration charts for the specific gas and pressure can be found above.
The pressure that you choose is the pressure that is in the tube. Most people have the valve on the inlet and the rotameter flows to an instrument or process at atmospheric pressure so in that case you would use the 0 PSIG charts. Do not use the pressure supplying the rotameter if the valve is on inlet. If your valve is on outlet of the rotameter then either use a pressure correction factor or use a calibration chart corresponding to the pressure in the tube. We have many charts that are for 20 PSIG and 50 PSIG.