Variable Area Flowmeter (Rotameter)
Product Overview
A Variable Area Flowmeter, commonly known as a Rotameter, is a simple and reliable flow measurement device used to measure the flow rate of liquids and gases. It consists of a tapered tube and a float that moves freely within the tube as fluid flows upward. As flow increases, the float rises, increasing the flow area until equilibrium is reached. Variable area flowmeters are widely used for their simplicity, low cost, visual indication, and minimal power requirements, making them ideal for local flow indication and basic process control.
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How it works (simple explanation)
- Fluid enters the flowmeter from the bottom and flows upward.
- The flowing fluid pushes the float upward inside the tapered tube.
- As the float rises, the flow area increases.
- The float stabilizes when the upward force of the fluid equals the weight of the float.
- The height of the float directly indicates the flow rate on a calibrated scale.
What it measures
- Volumetric flow rate of liquids or gases
- Local instantaneous flow indication
- With transmitters, can provide analogue or digital output signals
- They are best suited for steady, low to moderate flow rates and are commonly used where local visual monitoring is required.
Key advantages
- Simple mechanical design
- No external power required for basic operation
- Low pressure drops
- Cost-effective solution
- Easy installation and maintenance
- Visual flow indication
- Suitable for low flow applications
- Available in metal, glass, and plastic constructions
Applications
- Water and wastewater monitoring
- Chemical processing (acids, bases, solvents)
- Oil & gas auxiliary systems
- Food & beverage (process and utility fluids)
- Pharmaceuticals and laboratories
- HVAC systems
- Gas flow measurement (air, nitrogen, oxygen)
- Purge and sampling systems
Installation
- Must be installed vertically, with flow from bottom to top
- Ensure the meter is perfectly upright
- Avoid pulsating flow and vibration
- Provide clean fluid to prevent float sticking
- No long straight pipe runs required
- For pressurized systems, use metal tube rotameters
- Optional transmitters require proper electrical wiring
Technical Specifications
Parameter | Specification |
Measurement Principle | Variable area (float in tapered tube) |
Measured Media | Liquids and gases |
Flow Range | Very low to moderate (model dependent) |
Accuracy | ±1% to ±5% of full scale |
Repeatability | ±0.25% to ±1% |
Operating Pressure | Up to 400 bar (metal tube types) |
Operating Temperature | –20 °C to +300 °C (material dependent) |
Tube Materials | Glass, stainless steel, acrylic |
Float Materials | Stainless steel, PTFE, ceramic |
Output Options | Local scale, 4–20 mA, pulse (optional) |
Installation Orientation | Vertical only |
Power Requirement | None (mechanical), optional for transmitter |
Maintenance | Very low |