Positive Displacement
Technology

Positive Displacement Flow Meters are well suited for measuring the flows of viscous fluids or for use where a simple mechanical meter system is required.

Basic Elements of Design
Every positive displacement flow meter is composed of three component parts: external housing or body, the measuring unit, and the counter drive train. The meters operate by continuously dividing the flowing media into known volumetric increments, isolating these momentarily, and returning them to the flow stream while counting the number displacements. Oval Gear Flow Meters Oval gear flow meters are used primarily to measure volumetric flow of high viscosity fluids, such as: heavy petroleum products, epoxy resins, paints, etc. that are too difficult for most other types of flow meters, due to Reynold's number constraints. Incoming liquid (upstream pressure) exerts a pressure differential against the (upstream end) lower face of oval gear A, causing the two interlocked oval gears to rotate to position 2. In this second position, the flowing liquid enters the cavity between oval gear B and the flow meter body wall, while an equal volume of liquid simultaneously passes out of the cavity between oval gear A and the flow meter body wall. Meanwhile, upstream pressure continues to force the two oval gears to rotate to position 3. At this position, a predetermined quantity of liquid has again filled the cavity between oval gear B and the flow meter body. This pattern is continuously repeated moving four times the liquid capacity of each cavity with each revolution of the rotating gears. Therefore, the flow rate is proportional to the rotational speed of the gears.
Magnets, imbedded in each end of the rotating oval gears, are used to open and close a reed switch output signal , activate a microprocessor or Hall Effect Pickup to transmit the internal motion (rotational count) to a usable output signal. High Viscosity Service
The interaction of fluid viscosity and pressure drop across the meter can be significant to the quality of performance of an oval gear flow meter in high viscosity service.
As the viscosity increases, leakage through the meter decreases. This improves the accuracy of measurement at the lower end of the flow range. However, higher viscosity also increases the pressure drop across the meter. Maximum pressure drop limits maximum flow capacity in all positive displacement flow meters. Installation The oval gear meters are easy to install with no special upstream or downstream piping requirements.
Gear Flow Meter Index These rugged, precisely machined positive displacement flow meters are offered in a variety of designs, with a variety of counter drive train options to fit a wide range of flow measurement applications.