Volumetric flow meters count discrete volumes of fluid per revolution or oscillation — oval gear meters count precise gear chamber volumes; nutating disc meters count diaphragm oscillations per unit volume; rotameters (variable area meters) use the equilibrium position of a float in a tapered tube proportional to flow. Paddle wheel meters use a small rotor inserted in the flow stream. Processing 0.001 L/min to 3,000 m³/h, volumetric meters provide low-cost, mechanical, or simple electronic flow measurement for low-flow precision dosing, chemical injection, and general purpose liquid metering.
Oval gear: two meshing oval rotors turn in a close-tolerance chamber — each rotation displaces a fixed volume between gear and chamber wall. A pulse or reed switch counts revolutions, directly computing volume with no additional measurement parameter. Rotameter: fluid flows upward through a tapered transparent or metal tube, lifting a float to an equilibrium height where buoyancy plus drag equals float weight — float position (read visually or by magnetic follower transmitter) is proportional to volumetric flow rate. Paddle wheel: small impeller mounted tangentially in the flow stream rotates at speed proportional to velocity — low-cost alternative to turbine for clean water and cooling system applications.
Challenges
Oval Gear Stall at High Viscosity (>5,000 cP) — Gear Locked by Viscous Drag
Very high viscosity fluid generates drag exceeding gear drive torque — gear train stalls; no rotation; no output.
Rotameter Tube Breakage in Pressurised Glass Tube Installation
Borosilicate glass rotameter tube fractures from thermal shock, water hammer, or overpressure — hazard from pressurised fluid release.
Oval Gear Wear from Abrasive Particles or Fibrous Material
Abrasive particles jam gear mesh — rotor seizure; fibres wrap around rotor shaft — gradual wear shifts calibration.
Rotameter Accuracy Affected by Fluid Density and Viscosity Changes
Float equilibrium depends on fluid density and viscosity — any change from calibration conditions shifts reading by up to ±5%.
Paddle Wheel Fouling from Scaling or Biological Growth at Low Flow
Scale and biofilm on paddle blades add mass — rotation slows; under-reading; eventual seizure.
Solutions
- High-Viscosity Oval Gear: Use Helical Rotor (Worm Gear) Type — Handles Up to 100,000 cP: Helical rotor type displaces without meshing gear contact — operates in high-viscosity service without stall.
- Metal Tube Rotameter (SS 316L Float and Tube) for High-Pressure or Hazardous Service: Metal armoured tube with external magnetic follower indicator — no glass; rated to 250 bar; ATEX Zone 1.
- Inlet Strainer (40–80 mesh, SS 316L) Before Every Volumetric Meter: Strainer removes all particles above 50 µm — prevents gear wear, paddle fouling, and tube blockage.
- Rotameter Correction Factor Applied in Transmitter for Off-Calibration Density: Smart transmitter applies ρ correction — corrects reading when fluid density differs from calibration value.
- Paddle Wheel with Self-Cleaning Rotating Brush (Spring-Loaded): Brush assembly on paddle shaft — continuous self-cleaning removes scale; prevents seizure at low flow.
Applications
- Chemical Dosing: Oval gear for precise chemical injection metering — bleach, coagulant, acid, alkali dosing systems.
- Lubrication Systems: Oval gear for hydraulic oil, lubricant, and coolant flow monitoring on machinery.
- Utility Water: Rotameter and paddle wheel for cooling water, utility water flow indication — local visual indication.
- Analytical / Laboratory: Micro oval gear for laboratory sample collection, micro-dosing, and analytical instrument calibration.
- HVAC: Paddle wheel for chilled and hot water flow monitoring in building services.
Models & Capacities
Meter Type | Size DN [mm] | Flow Range | Accuracy [%] | Max Viscosity [cP] | Max Pressure [bar] | Max Temp [°C] | Output | Fluid Compatibility | Notes |
Oval gear (standard) | DN 6–DN 100 | 0.5 L/h–15 m³/h | ±0.1–0.5 | 5,000 | 100 | 150 | Pulse + 4–20 mA | Clean to moderately dirty liquids | Excellent for viscous fluids; no straight run required |
Oval gear (high-viscosity) | DN 10–DN 100 | 1 L/h–10 m³/h | ±0.2–0.5 | 100,000 | 50 | 150 | Pulse + 4–20 mA | Viscous oils, resins, adhesives | Helical/worm rotor; wide viscosity range |
Oval gear (sanitary) | DN 10–DN 80 | 0.5 L/h–12 m³/h | ±0.1–0.5 | 5,000 | 16 | 150 | Pulse + 4–20 mA | Food, beverage, pharma (CIP/SIP) | Tri-Clamp; Ra <0.8 µm; EHEDG/3-A |
Nutating disc | DN 15–DN 50 | 0.2 L/h–6 m³/h | ±0.5–1.5 | 500 | 16 | 90 | Pulse | Clean water, utility liquid | Low cost; water utility metering standard |
Rotameter (glass tube) | DN 4–DN 100 | 0.1 mL/min–10 m³/h | ±2–5% FS | 500 | 10 | 120 | Visual; 4–20 mA opt. | Clean liquid and gas, lab use | Simple, no power; requires vertical installation |
Rotameter (metal tube) | DN 10–DN 100 | 0.5 mL/min–8 m³/h | ±2–4% FS | 500 | 250 | 450 | 4–20 mA magnetic | All fluids including hazardous, steam | ATEX Zone 1 rated; wide temperature range |
Paddle wheel | DN 10–DN 500 | 0.1–15 m/s | ±1–3% FS | 200 | 25 | 120 | Pulse + 4–20 mA | Clean to lightly loaded water | Insertion or inline; lowest cost velocity type |
Pelton wheel (micro) | DN 1–DN 25 | 0.01 mL/min–5 L/min | ±0.5–1.5 | 100 | 350 | 120 | Pulse (high resolution) | Very clean low-flow liquids, reagents | Ultra-low flow; lab and analytical instrument |