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Bunker Oil Flow Meter 5 m3/h: Managing Viscous Resistance in Auxiliary Feed Lines
Quick Answer: For bunker oil flow measurement at 5 m3/h in auxiliary feed lines, an oval gear meter is the simplest reliable solution. It handles viscosities up to 2000 cP straight out of the box and delivers accuracy within ±0.5% of reading. A meter with at least DN25 size and heating jacket option prevents fuel solidification inside the measuring chamber.
Why Auxiliary Engine Bunker Oil Lines Need a Dedicated Flow Meter
Generators on large vessels and offshore platforms do not always run at full load. Auxiliary engines cycle between low idle and 85% load, and bunker fuel temperature at the engine inlet often sits between 120 and 140°C. At this temperature, IFO 380 viscosity falls into the 23 to 35 cSt range. The flow rate to a single gen set rarely exceeds 5 m3/h. A general-purpose meter placed in this line without considering viscous drag will under-report actual consumption by 4 to 7%. We have seen this multiple times on customer sites in Vietnam and Nigeria.
Viscous Resistance Inside a Small Bore Pipe
Pipe size for a 5 m3/h bunker oil line usually ends up as DN20 or DN25. At DN20 and 5 m3/h, the line velocity approaches 4.4 m/s. Bunker oil with a kinematic viscosity of 700 cSt at 50°C, common during preheating and start-up, behaves very differently than diesel. Pressure drop across a mechanical meter can jump to 0.8 bar. If the meter uses moving parts that rely on fluid momentum, such as a turbine wheel, the resistance alone can stall the rotor. An oval gear meter does not care about velocity profile. Two precision-machined oval rotors rotate in a positive displacement chamber. The only thing that matters is the volume moving through.
What Silver Instruments Recommends
Send us your pressure (bar), temperature (°C), pipe size (DN), and required flow range. We size the meter for the worst-case viscosity, not the running value.
For a 5 m3/h auxiliary feed line, we typically recommend the OGM series oval gear flow meter with DN25 flanges and PTFE gears. The output can be configured as a 4-20 mA HART signal or a frequency pulse, both readable by a standard PLC. If the engine room is classified, we supply the meter body with ATEX Zone 1 certification and an intrinsically safe pickup. The local display shows liters, kg, or barrels, selectable on site. For heavy fuel up to 2000 cP, we add a 24V DC cartridge heater on the body to keep the internal clearance stable.
A Real Shipyard Scenario
A ship repair yard in Batam, Indonesia, ordered three 5 m3/h bunker oil meters for auxiliary genset consumption monitoring in early 2024. The existing differential pressure flow meters were giving a negative offset of 9% compared to tank soundings. The root cause was changing viscosity during bunker switchover from HFO to MGO. We supplied oval gear meters with integrated Pt100 and a local flow totalizer. After commissioning, the deviation from soundings dropped to 0.8% at steady load.
Mounting and Pipework Notes
In practice, most engineers skip this part until the meter gives erratic readings. An oval gear m
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Other Meter Types for Bunker Oil at 5 m3/h
Coriolis mass flow meters work for bunker oil with viscosity up to 10000 cP. They give mass flow, density, and temperature directly. The downsides are higher cost and larger footprint. For a 5 m3/h line, a Coriolis meter with DN15 tube will create a pressure drop of 1.2 to 1.8 bar, which may require a booster pump on long auxiliary feed lines. Electromagnetic flow meters cannot measure heavy fuel oil because the fluid must be conductive beyond 5 µS/cm. Bunker oil is below 0.01 µS/cm. Thermal mass meters are not suited for viscous liquids either. Oval gear remains the most practical and budget-friendly choice for this flow rate.
Outputs and Remote Monitoring
We configure the meter with a 4-20 mA HART output so the engine monitoring system can trend flow and send alerts. The totalizer pulse outputs to the fuel transfer system or bunkering log. Our meters have an RS485 Modbus RTU option for simple connection to a PLC or SCADA. If the vessel operates in a region with poor satellite link, the local digital display with battery-powered backup keeps the reading visible.
FAQ
What flow meter works best for bunker oil at 5 m3/h?
An oval gear positive displacement flow meter with heating jacket is the most dependable choice. It handles the high viscosity of cold startup and the lower viscosity of hot running oil with the same accuracy class.
Can a Coriolis mass flow meter work on auxiliary feed lines?
Yes, a Coriolis meter works but costs three to five times more and can add 1.5 bar pressure drop in a DN15 line. If the line has a supply pressure above 5 bar, a Coriolis meter becomes feasible.
What pipe size do I need for 5 m3/h heavy fuel oil?
For bunker fuel up to 700 cSt, DN25 pipe is standard. If the fuel viscosity exceeds 1000 cSt at pumping temperature, we recommend DN32 to keep velocity below 2.5 m/s and reduce pressure loss.
Does Silver Instruments provide ATEX certified meters for marine use?
Yes. Our oval gear flow meters for bunker oil can be supplied with ATEX Zone 1 or Zone 2 certification. The pickup is approved for gas groups IIB and IIC, suitable for engine rooms.
How do you handle air pockets in the liquid?
An oval gear meter will read high if a large slug of air passes through. We add an air eliminator upstream when the line supply is from a day tank with a low head. This keeps accuracy within ±0.5%.
Send us your fuel viscosity (cSt), temperature (°C), pipe size (DN), and required flow range. We will size and price a meter for your auxiliary feed line within 24 hours. See our oval gear flow meter range for bunker and heavy fuel oils.
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