Oval gear flow meters are a type of positive displacement meter. As liquid flows through the meter, a pair of oval shaped gears are forced to rotate by the flow of the liquid. These gears mesh together & force a finite amount of fluid through the meter. A sensor or mechanical drive detects the rotation of the gears to determine the displaced volume of liquid. The faster the flow rate, the faster the gears turn.
Principles of Operation
The oval gear flow meter comprises oval-shaped, geared rotors which rotate within a housing of specified geometry. Fluid differential pressure causes the inter-meshing gears to rotate, trapping a ‘pocket’ of fluid between the gear and the outer housing and subsequently emptying the fluid pocket into the downstream flow. Capillary action of the metered fluid forms a liquid seal. Each ‘pocket’ holds a precise and known volume of fluid so counting the pocket frequency gives a measurement of the volumetric flow rate. This is typically achieved by embedding magnets in the rotors, which then actuate a reed switch or provide a pulse output as they rotate and thus flow is measured electronically.
OVAL Gear Flow Meter Advantages
• Traditional proven flow technology
• Simple to install
• No straight pipe runs required so flow meters can be installed in restricted areas
OVAL Gear Flow Meter Limitations
• Not suitable for steam or multi-phase fluids
• Fluid slippage adversely affects accuracy; this varies with flow rate, differential pressure, temperature, viscosity and clearance
• Not recommended for low-viscosity fluids, including water or water-like fluids (because of an increase in fluid slippage)
• Accuracy adversely affected by bubbles present in fluids
The oval gear flow meter is designed primarily for use with higher-viscosity fluids, which has led to applications such as the flow metering of oils, syrups and fuels.