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Oval Gear Flow Meters & Oval Gear Flow Sensors: Precision Volumetric Systems for Paints and Oils

Quick Answer: Oval gear flow meters are positive displacement instruments. They measure paints, oils, varnishes, and other viscous liquids with high repeatability at low flow rates. For most paint and oil processes, select a DN15 to DN80 meter with FKM or PTFE seals and pulse or 4-20 mA HART output.

Why Oval Gear Meters Fit Paint and Oil Batching

Here is the thing. Paint and oil flows are thicker than water and they can change viscosity with temperature. A turbine meter often struggles in these conditions. Oval gear flow meters do not rely on conductivity or high velocity. Two oval gears rotate inside a precision chamber. Each rotation moves a fixed volume from inlet to outlet.

Volumetric measurement is what paint batching and oil dosing need. A DN25 oval gear meter can measure 1 to 20 litres per minute with reading accuracy near plus or minus 0.5 percent. Repeatability usually lands near plus or minus 0.1 percent. In one paint plant in Vietnam, a 25 mm cast iron meter handled alkyd resin at 3,200 cP. The operator sent a 4-20 mA HART signal to the PLC and used pulse output for batch total. That setup replaced manual weighing and cut batch time by about 12 minutes per shift.

Selecting the Right Meter for Paints and Oils

Start with pipe size and flow range. DN15 suits 0.5 to 5 litres per minute. DN25 covers 1 to 20. DN40 covers 5 to 100. DN50 covers 10 to 200. DN80 covers 25 to 500 litres per minute. These ranges change with viscosity and back pressure. Send us your pressure (bar), temperature (°C), pipe size (DN), and flow range.

Material selection matters. Cast iron with FKM seals works for many solvent based paints and mineral oils. Stainless steel 316 body with PTFE or PEEK gears suits water based paints, inks, and aggressive solvents. Food grade paints and edible oils may need stainless steel with EPDM seals. Always check seal compatibility with ketones, esters, and aromatic solvents.

Temperature is another factor. Standard oval gear meters handle -20 to 120 °C. For hot oil or reactor discharge, specify PT100 temperature compensation and a high temperature gear set. Silver Automation Instruments offers PT100 integration on most DN15 to DN100 oval gear flow sensors.

Signal Output and Process Integration

Most engineers choose pulse output for simple batch controllers. Each pulse represents a fixed volume. The PLC counts pulses and converts them to total volume. For continuous paint mixing or oil blending, 4-20 mA HART gives flow rate. Some sites add Modbus RTU over RS485 for direct connection to a DCS or SCADA system.

We have seen this on customer sites many times. An oil blending plant in the United Arab Emirates runs four DN40 oval gear meters on one manifold. Each meter sends 4-20 mA HART to a flow computer. The pulse output runs a local batch controller. The plant fills IBC tanks with hydraulic oil and gear oil. Because the meter is positive displacement, flow pulsation does not cause false totals.

For hazardous areas, Silver Automation Instruments can supply oval gear meters with ATEX Zone 1 approval. Specify the gas group and temperature class with your inquiry.

Installation Tips That Prevent Meter Failure

Most oval gear meter problems come from dirt, air, or wrong pipe connection. Install a Y strainer or basket filter upstream. A 100 mesh strainer is common for paints. For heavy oils, use a 60 mesh strainer to avoid high pressure drop. Dirt or dried paint particles can jam the oval gears.

Air pockets cause the rotors to spin without moving liquid. That creates false counts. Mount the meter so liquid stays inside the measuring chamber. A back pressure valve downstream helps keep the chamber full with low viscosity oils and solvents. In practice, 0.5 to 1.5 bar of back pressure is en