Current position > Product detail
『Rotameter Flow Meter Selection: How To Choose Between Liquids And Gases』Related information(v cone flow meter|rotary gas meter|gallon meter|gear meter|metal tube rotameter|glass tube rotameter|nutating disk meter|transit time ultrasonic flow meter|wedge flow meter|pd meters|hydraulic flow meter|ultrasonic water flow meter|water flow meter|air flow meter|magnetic water flow meter|oxygen flow meter|gas flow meter|argon flow meter|air velocity meter|gasoline flow meter|fuel flow meter|ultrasonic water meter|digital water meter|nitrogen flow meter|solid flow meter|Oxygen tank flow meter|digital water flow meter|diesel fuel flow meter|steam flow meter|02 flow meter|compressed air flow meter|oil flow meter|liquid flow meter)
Rotameter Flow Meter Selection: How To Choose Between Liquids And Gases
Quick Answer: A rotameter measures flow using a float inside a tapered tube. The float position depends on fluid density. For liquids, you need actual density, viscosity, and temperature. For gases, you must correct for pressure, temperature, and molecular weight. Always define your media first. A water-calibrated rotameter will give a wrong reading on air if you do not convert the scale.
Why the liquid-gas choice matters in rotameters
Rotameters do not measure mass flow directly. They measure volumetric flow under the float density balance. A gas at 2 bar (g) has double the density of the same gas at 1 bar (g). So the same flow in standard liters per minute shows a different scale if you do not correct. Liquid density changes less with pressure but more with temperature. A hydrocarbon at 50 °C is less dense than at 20 °C. This shifts the float position.
Here is the thing. Most engineers skip this part and ask for a quote based on water or air. Then the meter reads off by 10 to 30 percent on site. We have seen this on customer sites many times, from a chemical dosing line in Peru to a hydrogen gas measurement in Oman. To avoid that, state your fluid name, operating temperature in °C, and pressure in bar (g).
Selecting a rotameter for liquids
Key parameters: density (kg/m³ or g/cm³), viscosity (cP), temperature, pipe size (DN), flow range (L/h or m³/h), and connection type (threaded or flanged).
A viscous liquid like honey at 5000 cP needs a different float and tube design than water at 1 cP. High viscosity dampens the float movement. Silver Automation Instruments offers metal tube rotameters with a viscosity damping guide that works for up to 100 cP for standard models. For higher viscosity, we install a larger guide cone.
Example: A paint manufacturer in Vietnam needed to measure solvent flow at 8 cP and 45 °C. We supplied a stainless steel rotameter, DN25, threaded BSP connection, with 4-20 mA HART output. The float material was 316L. They sent us the exact density (0.86 g/cm³) and flow range (50 to 500 L/h). We calibrated each unit at our factory. If you can provide those details, send us your liquid name, density, viscosity, temperature, and flow range. We will quote a meter within one business day.
For water and low-viscosity liquids, a glass tube rotameter is cost-effective. Silver Instruments supplies the SIL-RG series in DN15 to DN50, with threaded or socket connections. These are popular in water treatment plants in Malaysia and the Philippines for chemical dosing of sodium hypochlorite or caustic soda. The end connection is typically PVC or UPVC. Always specify the wetted material when the liquid is corrosive.
Selecting a rotameter for gases
Gases require more data. You must give the gas type, inlet pressure, temperature, and the reference conditions for your flow unit (such as 0 °C, 1 atm for Nm³/h or 20 °C, 1 atm for Sm³/h). Different countries use different norms. A biogas plant in Thailand asked for a rotameter to measure methane flow at
_600x400.jpg)
Metal tube rotameters with a 4-20 mA transmitter and local indicator are common for compressed air, nitrogen, natural gas, and argon. Our SIL-RM series handles up to 16 bar (g) and 120 °C. You can order with ATEX Zone 1 certification if needed for oil and gas sites in the Middle East.
A typical mistake: a customer orders an air-calibrated rotameter for oxygen service. Oxygen has a slightly different density than air. Plus safety issues. You must degrease the wetted parts for oxygen service. Silver Instruments offers oil-free cleaning and certificates per ASTM G93. Tell us the gas name and inlet pressure to get the right scale and safe construction.
Material and connection considerations
Glass tube rotameters are for low pressure (up to 10 bar) and non-corrosive fluids. The wetted parts include borosilicate glass, PTFE, and stainless steel float. For high pressure, use metal tube rotameters with 304 or 316L body. Flanged connections (DN15 to DN100) fit process lines. Threaded connections (NPT, BSP) suit small lines. For seawater desalination plants, we recommend 316L or duplex stainless steel to resist chloride pitting. A desalination plant in Kenya ordered ten 316L metal tube rotameters for chemical injection last year.
How Silver Automation Instruments helps you select
We do not just sell a meter. We check your process data and suggest the right combination of tube, float, and transmitter. We can provide an analysis certificate for the scale. Send us your fluid data: pressure (bar), temperature (°C), pipe size (DN), flow range, and whether you need 4-20 mA output or HART. Our engineers will reply with a data sheet and price. Typical lead time is 7-10 working days for customized scales.
Frequently Asked Questions
Can I use the same rotameter for liquid and gas? No. The scale is different because density and float buoyancy differ. You must order two separate tubes or a dual-scale option if the density difference is small, but it is not typical.
What viscosity limit do your rotameters handle? Standard glass tube rotameters work up to 10 cP without correction. Metal tube rotameters handle up to 100 cP with a viscosity guide. For higher viscosity, we use a larger float guide and recalibrate.
Do you provide ATEX certification for gas flow measurement? Yes. Our metal tube rotameter with 4-20 mA can be certified for ATEX Zone 1 or Zone 2. We need your gas group and temperature class.
How do you convert flow units from air to natural gas? We use the density ratio and compressibility factor. Give us the inlet pressure, temperature, and desired unit (Nm³/h or kg/h). We handle the calculation and mark the scale.
What is the delivery time for a rotameter with a custom scale? Typically 7 to 10 working days from order confirmation. If you need faster delivery, we can offer an electronic scale with a 4-20 mA output and a digital display that you can re-range in the field.