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Oval gear flow meters are one of the most reliable ways to measure diesel oil, because they are a type of positive displacement flow meter that measures volume directly, unaffected by the flow profile or by minor viscosity changes in the fuel. This guide covers how oval gear meters handle diesel specifically, how to size and accuracy-rate one for your application, and a real DN40 custody transfer case to show the selection process end to end.
Quick AnswerFor diesel oil, an oval gear flow meter gives ±0.5% accuracy as standard, or ±0.2% on request, and needs no straight pipe run before or after installation. Diesel viscosity runs about 2 to 4 cSt at 40°C (104°F), well within the working range of an oval gear meter, which handles fluids from roughly 0.8 up to 2000 mPa.s (cP). Sizes run from DN2 up to DN200 (8 inch), in cast iron, cast steel, or stainless steel, with a mechanical register, or a digital version with 4-20 mA, pulse, RS485 Modbus, or HART output. |
An oval gear flow meter is a type of positive displacement flow meter, and it can measure varies kinds of oil, such as diesel oil, vegetable oil, edible oil, palm oil, gasoline, and heavy oil. Oval gear flow meters are widely used in factories, custody transfer stations, and the marine industry. The traditional design comes with a mechanical register and, on request, a return-to-zero totalizer. Digital versions are also available, with 4-20 mA analog output, pulse output, RS485 Modbus RTU communication, and even HART protocol.
For diesel oil specifically, oval gear meters are a strong fit. Diesel viscosity typically runs 2 to 4 cSt at 40°C (104°F) and changes with ambient temperature, and the meter maintains good accuracy across that range. It tolerates diesel with minor particulates and operates reliably from -20°C to +80°C (-4°F to 176°F). With ±0.5% accuracy as standard, it meets custody transfer requirements for truck loading, fuel dispensing, marine bunker metering, and factory consumption monitoring.
a. Oval flow meter measurement provides high accuracy. The basic error is generally 0.5% of reading, with 0.2% of reading or better available on special request. This makes it well suited to sites where high precision measurement is required.
b. There is no strict requirement on the viscosity of the diesel oil. Even higher viscosity diesel blends can still be measured accurately.
No straight pipe needed before and after oval gear flow meter
c. Pipe vibration and interference at the installation site have no effect on this flow meter, and an oval gear flow meter does not need a straight pipe run before or after installation.
d. With on-site direct reading through a mechanical register, no external power supply is needed. You can read the cumulative total directly, with a clear display and simple operation.
e. Chinese oval gear flow meter manufacturers now offer meters with more advanced functions, including digital display, 4-20 mA output, pulse output, RS485, and even HART protocol.
Small oval gear flow meter for low flow diesel
Before requesting a quote, it helps to confirm four things: your normal flow rate and range, your line size, your operating pressure and temperature, and whether you need a mechanical register or an electronic output. Oval gear flow meters for diesel are available from DN2 up to DN200 (8 inch), so both small dosing lines and large bulk transfer lines are covered by the same technology.
| Parameter | Value |
| Accuracy | ±0.5% of reading standard, ±0.2% of reading on request |
| Viscosity range | About 0.8 to 2000 mPa.s (cP), diesel itself runs 2 to 4 cSt at 40°C / 104°F |
| Size range | DN2 to DN200 (8 inch) |
| Operating temperature | -20°C to +80°C (-4°F to 176°F), extended ranges available |
| Body material | Cast iron, cast steel, or stainless steel 304 / 316 |
| Output options | Mechanical register, or digital with 4-20 mA, pulse, RS485 Modbus RTU, or HART |
| Straight pipe requirement | None needed upstream or downstream |
Material choice depends on the diesel grade and the site environment. Cast iron is the standard, economical choice for clean, non-corrosive diesel. Cast steel is a step up for higher pressure lines. Stainless steel 304 or 316 is worth the extra cost where the meter sits outdoors in a corrosive coastal or marine environment, or where the diesel is blended with biodiesel that can be mildly more aggressive on wetted parts over time.
One point worth flagging honestly: oval gear meters are only suitable for clean diesel. If the fuel carries particulates or dirt, install a filter upstream, since trapped particles can jam or wear the gears over time. On larger diameter meters, the cast iron or cast steel body also gets heavy, which is worth factoring into freight cost and mounting design for shipboard or skid installations.
Below is a real case where an oval gear flow meter used to measure diesel oil was selected for a customer, showing the specification and selection process in full.
The customer's original request, with metric and imperial units added for reference:
| Parameter | Value |
| Measuring medium | Diesel oil |
| Flow range | 0.6 to 5 m³/hr (2.6 to 22.0 GPM) |
| Nominal pressure | 221 psi (about 15.2 bar) |
| Process connection size | 40 mm (DN40, 1.5 inch NPS) |
| Housing material | Cast iron |
| Main body cover material | Cast iron |
| Rotor and chamber material | Cast iron |
| Process temperature | -20 to +80°C (-4 to 176°F) |
| Viscosity range | 0.8 to 400 mPa.s (cP) |
| Process connection flange | ASME 150 lb |
| Signal output | None, mechanical type only, no power available at site |
| Accuracy | ±0.5% of reading |
| Register | Local mechanical register, return-to-zero requested |
| Operational temperature range | -40 to +70°C (-40 to +158°F) |
| Display unit | Liter |
| Indicator | Mechanical pointer, 6-digit totalizer, return-to-zero |
The customer also asked for the gross shipping weight, since oval gear meters at this size are heavy enough to affect freight cost.
After checking all the specifications, we confirmed our LC-40 oval gear flow meter could do the job. Model selection breakdown:
| Parameter | Value |
| Model code | LC-NA40.2/A6 |
| LC | Silver LC series oval gear flow meter |
| N | High viscosity type, for viscosity over 200 mPa.s |
| 40 | Flow meter size, 40 mm (DN40) |
| .2/ | Operating pressure rating, 1.6 MPa (232 psi) |
| A6 | Mechanical display, 6-digit totalizer, return-to-zero register |
| Gross weight after packing | 28 kg per unit (about 61.7 lb) |
| Delivery time | 7 to 10 working days after payment received |
Full catalog reference: Oval Gear Flowmeter.
Because oval gear flow meters get heavy at larger sizes, some customers choose liquid turbine flow meters as a lighter alternative for diesel oil measurement. The trade-off is that turbine meters only work well with low viscosity, clean oils, while oval gear meters keep working accurately up to about 2000 mPa.s (cP).
For more demanding applications, such as bitumen or heavy fuel oil that runs much thicker than diesel, a Coriolis mass flow meter is usually the better choice, since it measures mass directly and is not affected by viscosity changes at all.
Silver Automation Instruments is a professional oval gear flow meter supplier. We manufacture oval gear meters in sizes up to DN200 (8 inch) in cast iron, cast steel, stainless steel 304, and stainless steel 316, to match diesel, fuel oil, and other liquid duties.
Send your diesel flow range (m³/hr or GPM), pipe size (DN or inch), operating pressure and temperature, and whether you need a mechanical register or an electronic output (4-20 mA, pulse, RS485 Modbus, or HART) to sales@silverinstruments.com. We will confirm the right LC series model, material, and lead time, along with the shipping weight for your project.
