Purge / Low-Flow Rotameter – Working Principle, Specifications & Industrial Applications
A Purge / Low-Flow Rotameter is a precision variable area flow meter designed specifically for low flow measurement of gases. It provides accurate flow control and monitoring for purge lines, sampling systems, analyzer gas supply, and laboratory applications.
Sai Tech Flow manufactures high-quality purge rotameters that are widely used in chemical, pharmaceutical, petrochemical, and utility systems, ensuring reliable operation, repeatable measurement, and easy installation.
These rotameters are ideal for delicate gas flows, where precise control is critical to protect process equipment, analyzers, or sensitive instrumentation
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What is a Purge / Low-Flow Rotameter?
A Purge or Low-Flow Rotameter is a vertical flow meter consisting of:
- A transparent tube (Acrylic or Borosilicate Glass depending on design)
- A float inside the tube that rises according to flow rate
- A calibrated scale for direct reading
It operates on the variable area principle, where upward drag force of the gas balances the downward gravitational force of the float. The float stabilizes at a height representing the current flow rate, allowing visual monitoring and precise control.
These rotameters are designed for very low flow ranges, typically from 0.1 LPM to 50 LPM (liquids or gases), making them ideal for gas purging and analyzer calibration systems.
Working Principle
The working principle is based on variable area and gravitational balance:
- Gas or liquid flows upward through a tapered vertical tube.
- The float rises until equilibrium is achieved (upward force = float weight).
- The float position corresponds to the flow rate, which is read directly from the calibrated scale.
Special Features for Low-Flow Measurement:
- Fine-calibrated float for high sensitivity
- Optional needle or control valve for precise flow adjustment
- Protective housing to prevent float wobble and external impact
Construction & Design Features
Sai Tech Flow’s Purge / Low-Flow Rotameters are engineered for accuracy, durability, and reliability.
Key Components:
- Tube Material: Acrylic or Borosilicate Glass (transparent)
- Float Material: Stainless Steel / PTFE / Ceramic (chemical compatible)
- End Connections: Flanged & Threaded (BSP / NPT) – Sai Tech Standard
- Working Pressure: Up to 10 bar
- Operating Temperature: Up to 100°C
- Flow Scale: Engraved or printed scale (SCFH, Nm³/hr, LPM)
- Optional Flow Control Valve: For precise purge or analyzer flow
- Protective Guard: Metal enclosure optional for additional safety
Technical Specifications (Sai Tech Flow Standard)
Parameter | Specification |
Flow Medium | Gas / Low-Flow Liquid |
Tube Material | Acrylic / Borosilicate Glass |
Float Material | SS316 / PTFE / Ceramic |
Flow Range | 0.1 to 50 LPM (Gas) / 10 LPH to 100 LPH (Liquid) |
Pressure Rating | Up to 10 bar |
Temperature Range | Up to 100°C |
Connections | Flanged & Threaded (BSP/NPT) |
Mounting Orientation | Vertical — upward flow only |
Accuracy | ±2% FSD (approx.) |
Advantages of Purge / Low-Flow Rotameter
- High precision for low flow rates
- Direct visual monitoring
- Lightweight and easy to install
- Durable with protective housing
- Optional control valve for fine adjustment
- Suitable for gas purging, sampling, and analyzer lines
- Chemical resistance with proper float material selection
Industrial Applications
Purge / Low-Flow Rotameters are widely used in:
- Chemical & Petrochemical Plants – Purging of reactor and pipeline lines
- Gas Analyzer Lines – Precise flow to analytical instruments
- Pharmaceutical & Biotech – Low-flow monitoring in lab and process equipment
- Water & Wastewater Treatment – Chemical dosing and gas aeration control
- Food & Beverage – Low-flow gas or liquid injection lines
- OEM & Skid Systems – Integrates easily with pilot plant skids or gas supply systems
- Utility Gas Lines – Nitrogen, Hydrogen, or compressed air for purging
They are essential wherever precise low flow is required, preventing instrument damage or process errors.
Purge / Low-Flow vs Standard Rotameters
Feature | Purge / Low-Flow Rotameter | Standard Rotameter |
Flow Range | Very Low (0.1–50 LPM) | Medium to High |
Tube Material | Acrylic / Glass | Glass / Acrylic / Metal |
Application | Gas purging, analyzer lines | General flow measurement |
Accuracy | Very High (for low flows) | Moderate |
Control Valve | Often included | Optional |
Industrial Use | Sensitive systems | General process systems |
Conclusion: Purge / Low-Flow Rotameters are specifically designed for high-precision, low-flow applications where standard rotameters cannot provide sufficient sensitivity or control.
About Sai Tech Flow – Manufacturer & Supplier
Sai Tech Flow is a trusted manufacturer and supplier of precision flow instruments in India. Our Purge / Low-Flow Rotameters are engineered for accuracy, durability, and industrial compliance, making them ideal for chemical, pharmaceutical, lab, and utility applications.
We offer custom flow ranges, flange & threaded connections, corrosion-resistant floats, and optional control valves, ensuring our rotameters meet the exact process requirements of our clients across domestic and international markets.
