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Macnaught Oval Gear Flow Meters: Accurate Positive Displacement Tools for Viscous Service
Macnaught oval gear positive displacement meters measure viscous fluids with plus-minus 0.5% repeatability. They suit diesel, heavy fuel oil, chemicals, and food-grade products from 0.5 cP to over 1,000,000 cP. Silver Instruments supplies the M and MX series across Australia, Southeast Asia, and the Middle East, with typical stock in Sydney and Nanjing.
Imagine a flow meter that does not care if your liquid is sticky, thick, or changes viscosity with temperature. That is what the Macnaught oval gear design achieves. Two precision oval rotors rotate inside a measuring chamber. Each rotation displaces a known volume. The result is a direct reading tied to shaft revolutions. No velocity profiles, no Reynolds number corrections. You get a stable signal even when the flow drops below 1 liter per hour.
We have seen this on customer sites many times. A chemical blender in Thailand ran their positive displacement pump at low speed. The oval gear meter still gave a clean pulse train. A turbine meter would have stalled. That is why engineers choose oval gear for custody transfer of fuel oil and batch dosing of additives.
Why Macnaught Oval Gear Meters Work Where Others Fail
Positive displacement meters do not rely on fluid velocity. Viscosity acts as a lubricant, reducing internal slip. The higher the viscosity, the better the accuracy. Macnaught models maintain linearity from 1 cP solvents to 1,000,000 cP polymer melts. Standard accuracy is 0.5% of rate, with 0.2% optional after calibration. Turndown ratios reach 100:1 on some models, so one meter covers multiple batch sizes.
Materials matter. Macnaught offers aluminum, stainless steel, and PPS (polyphenylene sulfide) bodies. Gears come in PPS, stainless steel, or PEEK. Seals range from FKM to PTFE. This lets you handle aggressive media like sulfuric acid or hot vegetable oil. For food processing, 3-A certified versions are available with Tri-Clamp connections.
M Series and MX Series Quick Reference
M Series (Aluminum): DN15 to DN80. Flow from 0.5 L/h to 400 L/min. Pressure rating up to 50 bar. Temperature -20 °C to 80 °C. Ideal for diesel fuel, lube oil, and non-corrosive liquids. Pulse output standard, 4-20 mA with display optional.
MX Series (Stainless Steel): DN10 to DN50. Handles up to 100 bar on selected sizes. Fluid temperature up to 150 °C. Used for chemicals, solvents, and high-temperature oils. ATEX Zone 1 and Zone 2 certification available.
Both series accept a PT100 temperature sensor for mass flow computation. Linearization tables can be stored in the companion display. Silver Instruments pre-programs these meters for your liquid type and unit preference, whether kg/h, L/min, or m3/h.
Real-World Installations
A paint manufacturer in Indonesia replaced a failing turbine meter on their resin batching skid with a Macnaught MX40. Resin at 8,000 cP was causing bearing wear. The oval gear unit with tungsten carbide bearings has run for 18 months without drift. They now batch 500-liter containers with repeatable accuracy under 0.3% of actual volume.
Last year a biodiesel exporter in Malaysia needed to measure heated palm oil methyl ester before loading onto trucks. The Macnaught M80 with high-temperature PTFE seals and a pulse output co
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A marine services company in Dubai uses a dozen Macnaught M15 meters for bunker fuel oil measurement on small vessels. The meters survive vibration and salty air because the aluminum body is hard-coated. Pulse outputs feed a PLC with Modbus gateway. This simple setup replaced manual dipsticks and cut transfer time by 30%.
Signal Integration Options
Every Macnaught meter comes with a reed switch or Hall effect pulse output. That is the cleanest way to interface with PLCs, batch controllers, and flow computers. We also supply the FLOseries companion display that converts pulses to 4-20 mA, scaled pulse, or Modbus RTU. The display stores totalizer data and provides a local readout. If you need IS (intrinsically safe) barriers, we include them in the quote. ATEX/IECEx certification covers gas zones 1 and 2, as well as dust zones 21 and 22.
How to Order from Silver Automation Instruments
Tell us your application and we will spec the right meter. Send your fluid name, viscosity in cP, normal and maximum flow rate, pipe size (DN), operating pressure in bar, and temperature in degrees C. Also let us know if you need ATEX, food-grade, or pulsed/NIMUR outputs. Reach Silver Instruments at [email protected] or call +86-135-1213-1526. For faster chat, use WhatsApp 86-135-12131526 or WeChat +86 13512131526. We serve customers in Australia, New Zealand, Vietnam, Indonesia, the Middle East, Africa, and Latin America.
Frequently Asked Questions
Q: What is the maximum viscosity a Macnaught oval gear meter can handle?
A: The M and MX series can measure up to 1,000,000 cP with no loss of accuracy. For extremes above 500,000 cP, we recommend heated housings and hardened bearings. Silver Instruments can advise based on your fluid data sheet.
Q: Can these meters handle abrasive or dirty liquids?
A: Yes, but you should install a Y-strainer upstream. Macnaught gears tolerate particles below 50 microns. For slurries, we suggest stainless steel rotors and an MX series meter. Regular flushing extends service life.
Q: Do you offer ATEX or IECEx certified oval gear meters?
A: Absolutely. We supply Macnaught MX meters with ATEX II 2G Ex ia IIC T4 certification for Zone 1. These meters are also available with SIL 1 rated pulse outputs for safety systems. Contact us with your hazardous area classification drawing.
Q: How do I choose the right line size?
A: Pipe diameter is a starting point, but flow range matters more. A DN25 meter can handle 0.5 to 30 L/min for diesel, for instance. Undersizing causes excessive pressure drop. Oversizing loses low-flow resolution. Share your min, normal, and max flow rates and we will select the optimal size.
Q: What is the typical lead time for a Macnaught meter shipped to Australia or Asia?
A: Standard models in aluminum are often in stock in Sydney and can ship within 3 business days. Stainless steel or ATEX versions require 2 to 4 weeks. Air freight to Southeast Asia adds 3 to 5 days. Sea freight for bulk orders takes 2 to 3 weeks. We give you a firm delivery date before you place the order.
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