Volumetric Flow Meter (Oval-Gear Type)

Function

Each revolution of the oval-gear pair displaces a fixed, precisely known volume of fluid regardless of viscosity, pressure variation or flow rate within the rated range. This is the key advantage over velocity-based flow meters — turbine or ultrasonic types — which would read inaccurately as bitumen viscosity changes with temperature during a long spray run. The meter's calibration factor in pulses per litre is stable over a viscosity range of 100–5,000 mPa·s, meaning the application rate display remains accurate throughout the run without manual compensation by the operator.

Construction & quality

Body: cast iron or 316 stainless steel to suit the operating environment. Oval gears: PEEK polymer — self-lubricating in bitumen, dimensionally stable to 180 °C — or stainless steel for aggressive grades. Shaft bearings: PTFE-lined or ceramic, rated for continuous high-temperature service. Sensor: Hall-effect proximity or reed switch, magnetically coupled through the body wall with no shaft penetration, eliminating a dynamic seal at the sensing point. Signal output: NPN open-collector pulse. Process connections BSP or flanged, DN25 to DN65.

When to replace

• Application rate display shows zero or a frozen value despite the pump running — sensor or gear failure
• Displayed flow rate is erratic or fluctuates unreasonably at steady pump speed
• Gear pair seized — pump delivery pressure rises abnormally and flow drops
• No pulse output from the sensor head, confirmed with a multimeter or pulse counter
• Meter body weeps bitumen at flange joint faces