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Rotameter Models and Indicators: Simple Variable Area Flow Tracking for Gas and Liquid

Quick Answer: Rotameter models track gas and liquid flow with a simple variable area design. Most plants use metal tube rotameters for high pressure lines and glass tube rotameters for low flow water or air. Send us your fluid, pipe size DN, flow range, pressure bar, and temperature degrees C to get a direct quote from Silver Instruments.

What Is a Rotameter in Industrial Flow Measurement?

A rotameter is a variable area flow meter. Rotameter models and indicators cover a wide range of gas and liquid duties. A float sits inside a tapered tube. Fluid passes upward through the tube. The float rises until the area around the float matches the flow rate. You read the flow on a local scale. Many models include a pointer indicator on a magnetic coupling. The design needs no external power for the local display. Typical accuracy is 1.6 percent to 2.5 percent of full scale. We supply rotameter models for water, air, nitrogen, light chemicals, diesel, and low viscosity oils.

Common Rotameter Models for Gas and Liquid

Glass tube rotameters suit low flow water and air. Sizes often start at DN15 and go up to DN50. A lab water skid may run a DN15 glass tube meter for 0.5 to 5 L/min. A wastewater sampling line may use a DN25 unit for 1 to 10 L/min.

Metal tube rotameters suit higher pressure gas and hot liquid. Sizes start at DN15 and run to DN100 or DN150 depending on the body rating. A chemical plant in Thailand might use a DN25 stainless steel rotameter for 20 percent caustic dosing at 100 L/h. A natural gas line in Indonesia might use a DN50 metal tube rotameter for 10 to 100 Nm3/h at 6 bar.

Purge rotameters handle very low gas flow. They often appear on analyzer panels and sample lines. Ranges can be 0.2 to 2 L/min of air or 0.05 to 0.5 L/min of nitrogen. Panel mount models save space and give a direct reading for maintenance teams.

Armored rotameters work in tough outdoor locations. The body is stainless steel. The indicator is sealed. These units are common in marine engine cooling loops and offshore skids. We have seen many of these on customer sites in the Middle East and Southeast Asia.

Rotameter Indicators and Output Options

A local mechanical indicator is standard on most metal tube rotameters. The float magnet couples to a pointer. The scale can be engraved in L/h, m3/h, kg/h, or percent. A direct reading scale reduces operator error.

Electronic transmitters add a 4-20 mA HART signal. The two wire output connects to a PLC or a paperless recorder. Some models include two alarm switches. The switches trigger at low flow or high flow setpoints. For hazardous areas we supply ATEX Zone 1 approved transmitters. For simple local indication no power is needed.

If you need temperature compensation for gas flow, a rotameter is not the best fit. In practice, a thermal mass flow meter works better for changing gas temperature and pressure. We can tell you which model fits after you send process data.

How to Select a Rotameter Model

Start with the fluid. Check if the fluid is gas or liquid. Check if the fluid is clean or dirty. Rotameters work best with clean fluids. Particles can jam the float. Viscosity above 50 cP may require special calibration. For diesel, light oil, and water, a standard metal tube rotameter works well.

Then define flow range. Give us the minimum and maximum flow in L/h, m3/h, or kg/h. Most engineers skip this part and oversize the meter. A rotameter reads accurately only in the upper 70 percent of the scale. For a DN25 water rotameter, the common range is 100 to 1000 L/h. For a DN50 gas rotameter, the range can be 10 to 100 Nm3/h at standard conditions.

Then define process conditions. Send us pressure bar, temperature degrees C, pipe size DN, and flow range. We can quote th