Company Profile

Dwyer Rate-Master and Visi-Float Tapered Acrylic Gas Tubes for Industrial Gas Flow

Quick Answer: The Dwyer Rate-Master and Visi-Float tapered acrylic gas tubes are direct reading flow meters for clean gas at low to medium flow rates. They suit air, nitrogen, oxygen, and inert gas lines in panel mount or inline service. Silver Automation Instruments supplies these Dwyer models with configuration support for industrial users in Southeast Asia, the Middle East, Latin America, and Oceania.

What the Rate-Master and Visi-Float Series Cover

Rate-Master meters are panel mount designs. The acrylic body keeps the unit light and easy to read. The Visi-Float series includes more inline and direct mount options with the same tapered tube principle. These are not high pressure devices. They solve low flow gas measurement where a turbine or Coriolis meter is too large or too expensive.

We see these meters in wastewater ozone skids, nitrogen purging on chemical reactors, food packaging gas flush systems, and burner air supply lines. A customer in Vietnam once asked us for a Visi-Float meter on a nitrogen purge line at 2 bar gas pressure and a range of 5 to 50 L/min. The meter worked because the gas was clean and the pipe size was small.

How the Tapered Tube Design Works

A float moves inside a tapered acrylic tube. Gas enters at the bottom. The float rises until the area around the float creates enough pressure drop to balance the float weight. You read the flow rate from the scale printed on the tube. No power supply is needed. No transmitter is required.

Here is the thing about this design. It is simple but it depends on gas density and pressure. The scale is calibrated for a specific gas at a specific pressure and temperature. If you run the meter on a different gas, the reading shifts. Most engineers skip this point and then wonder why the reading is off.

Because the tube is acrylic, the meter suits clean gas only. Wet gas, liquid slugs, or dirty gas can damage the float or make the tube hard to read. In practice, a 5 micron filter before the inlet solves many issues on compressed air lines.

Key Specifications to Check Before You Order

The standard accuracy for many Rate-Master and Visi-Float models is around 3 percent to 5 percent of full scale. The maximum pressure rating for standard acrylic bodies often sits near 6.9 bar at 21 degrees C. Some models go higher with metal housing options. Temperature limits are commonly 65 degrees C for continuous service. The connection size can be 1/8 inch, 1/4 inch, or 3/8 inch NPT. Some metric fittings are also available.

Do not use these meters for aggressive gases like wet chlorine or sulfur dioxide. The acrylic body and standard seals cannot handle those conditions. For aggressive chemicals, a thermal mass flow meter or a Coriolis meter from Silver Automation Instruments is a better fit.

Selecting a Model for Your Gas Line

Start with three data points. State the gas type, the normal flow rate, and the operating pressure. Then state the connection size and whether you need a panel mount or inline body. For example, a biogas project in the Philippines may need a 0 to 200 L/min air flow range on a 1/4 inch line. A food packaging customer in Brazil may need a 0 to 5 L/min nitrogen flow range with a needle valve.

The Rate-Master RMB series is often used for panel mounting in laboratories and gas analyzers. The Visi-Float VFA series is used for simple inline gas flow checks. Both series can include options like brass or stainless steel fittings, needle valves, and adjustable scales. We often ask for a photo of the installation point because the fitting orientation matters.

Installation and Maintenance Notes

Mount the meter vertically. A tilted meter changes the float position and gives an incorrect reading. Inst