Oval gear flow meters are traditional, mechanical, positive displacement (PD) flow meters, first invented more than 50 years ago by OVAL Corporation of Japan and now widely used for flow metering applications. Oval gear meters measure flow by employing a geared rotor to pass known volumes of a fluid through a housing.
Principles of Operation
A very precisely adjusted gear pair within the casing forms the measuring element. The inflowing medium causes the gear pair to rotate. The rotary motion is scanned by contactless sensors.Since each individual tooth generates a pulse, this results in a very high resolution. Consequently, even the smallest volumes can be measured or dosed precisely.The measurement unit contains two pick-offs that are circumferentially offset by ?of a tooth pitch to generate a 2 channel flow-proportional frequency signal. Suitable processing of the signal provides an greater resolution and the option to identify the flow direction. Basically, the measurement accuracy increases with increase in viscosity of the media.
The oval gear flow meter comprises oval-shaped, geared rotors which rotate within a housing of specified geometry. Fluid differential pressure causes the intermeshing 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.
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
Applications: 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.