A variable area flowmeter — commonly known as a rotameter — is one of the simplest and most cost-effective instruments for measuring the flow rate of gases and low-viscosity liquids. It consists of a vertically mounted, upward-tapered transparent tube with a float inside. As flow increases, the float rises to a higher position in the tube, where the wider cross-section allows equilibrium to be maintained. The float position is read directly against a calibrated scale on the tube — no power supply is required for local flow indication.

Variable area flowmeters are well suited to applications where simplicity, reliability, and low installation cost are priorities. With no straight pipe run requirements and a compact form factor, they are easy to install in tight spaces and existing pipework. All sensors are calibrated with traceability to USA NIST and the UK Accreditation Service (UKAS), and are manufactured under ISO 9001 quality conditions.

Description

What can it measure?

The variable area flowmeter measures:

• Instantaneous volumetric flow rate — read directly from the calibrated scale
• Gases: air, nitrogen, oxygen, CO₂, helium, propane, natural gas, and other process gases
• Liquids: water and low-viscosity liquids with specific gravity correction

Typical Applications

Variable area flowmeters are used wherever a simple, visual flow indication is needed. Typical applications include:

• Compressed air monitoring — plant air systems, pneumatic circuits, and purge lines
• Process gas flow indication — nitrogen blanket, CO₂ sparging, and inert gas purging
• Cooling water and utility water monitoring
• Laboratory and analytical instrument gas supply control
• Chemical dosing and reagent feed lines
• Food and beverage — sanitary versions for CIP and process lines
• Pharmaceutical and biotech — sanitary Tri-Clamp and DIN 11851 connection variants
• Panel-mounted flow indication for skid packages and control panels
• Low-flow metering for purge, bleed, and seal gas applications

Key Advantages

• No power required for local flow indication — completely passive visual reading
• Simple construction — transparent borosilicate glass tube with a single float, minimal maintenance
• No straight pipe runs required — installs directly into existing pipework
• Wide range of construction materials — stainless steel, PTFE, aluminium, and plastic versions
• Sanitary versions available — Tri-Clamp and DIN 11851 connections for food, beverage, and pharmaceutical applications
• Panel-mount versions for skid integration and control panel installation
• Flanged versions for process plant installation (ANSI 150, DIN PN10, JIS 10k)
• Optional flow switches for high or low flow alarms
• Calibrated with traceability to USA NIST and UK UKAS international standards
• Manufactured under ISO 9001 quality conditions
• Meets European Pressure Equipment Directive (PED 97/23/EC) and EMC Conformity (EN 61326)

Available Configurations

• Panel-mount (miniature) — compact borosilicate glass tube, 1/8″–1/4″ connections, ideal for instrument panels and skids
• Polished stainless steel industrial — threaded or sanitary connections for clean and hygienic environments
• Metal-encased with viewing window — maximised flow tube protection, threaded or flanged connections
• Wide-view metal-encased — larger viewing window for easier reading in the field, threaded or flanged
• Plastic rotameter — PVC/acrylic construction for corrosive or chemically aggressive liquids, optional flow switches

Variable area flowmeters are sized based on media type, flow rate range, operating pressure, and temperature. Corrections are applied for gases and liquids other than the reference media. Our specialists can assist with the correct sizing for your application.

Click here to contact our team for sizing assistance or to request a quotation.