What are Rotating Vane Flow Sensors/Meters?

How they work, where they excel, advantages and limitations.

How they Work:

Rotating Vane flow technology is also commonly known as paddle-wheel technology. There are a few different variations of rotating vane technology. All of them involve a rotor or paddle-wheel that spins on an axis due to media flow. The difference between the types lies in the paddle-wheel and flow orientation.

True "paddle-wheel" technology has flat rotor blades that behave in a manner similar to a riverboat paddle-wheel. The flow contacts the rotor in an "overshot" manner. Turbine type models have angled or twisted rotors that essentially face the flow straight on, or in other words, the flow is parallel to the axle. This type of motion is replicated in boat motors, wind mills, airplane engines, and simple house fans. Pelton-wheel technology is very similar to the "paddle-wheel" as it also has flat rotor blades, but the flow is concentrated around most of the paddle, not straight across it which gives it higher accuracy than the "paddle wheel type".

In any of these types, the rotational speed of the wheel or blade is a direct function of the volumetric flow rate. This motion is detected electronically by a magnetic pick-up, an inductive pick-up, or an optical detection. A frequency output is then either used directly or converted to a proportional analog signal.

Types of Rotating Vanes:

• Paddle-Wheel
• Pelton-Wheel
• Turbine

Advantages:

• Economical solution
• Fast response and repeatable
• Easy to install and maintain
• Universal mounting (no paddle face-up)
• Direct volumetric flow measurement
• Some provide visual indication
• Material flexibility
• Can be coupled with electronics
• Minimal pressure drop
• Can sense low flow rates

Considerations:

• Over-ranging causes excessive wear
• Any ferrous particles have to be filtered
• Magnetic particles can impede output
• Dark media can block inferred signal
• Pipe must be full for accurate readings

Common Applications:

• Cooling Towers/ Chillers
• Dispensation/Batching Systems
• Flow Verification and Monitoring
• Protection of Pumps
• Fume Scrubbers
• Medical Equipment
• Reverse Osmosis
• Filtration and Irrigation

Limitations:

• Not usually bi-directional, but can be
• Primarily for clean, low viscosity media
• Straight pipe run requirements

Sample Media:

• Water
• Low Viscosity Liquids
• Aggressive Chemicals