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Oval Gear Flow Meters and Positive Rotary Hardware for High-Repeatability Fuel and Oil Measurement

Quick Answer: Oval gear flow meters are positive rotary hardware that give repeatability of ±0.03 percent and accuracy of ±0.2 percent of reading for diesel, heavy fuel oil, lubricants, and clean viscous liquids. Pulse and 4-20 mA HART outputs connect to most PLC and batch controllers. Send us your fluid type, viscosity in cP, flow range, pressure in bar, temperature in °C, and pipe size in DN for a specific quote.

Why Positive Displacement Design Fits Fuel and Oil Service

Oval gear meters belong to the positive displacement flow meter family. Two oval rotors mesh inside a precision chamber. Each rotation sweeps a fixed volume from inlet to outlet. That fixed volume is the reason the meter keeps high repeatability even when flow rate changes. In practice this matters for diesel dispensing, burner fuel feed, and oil blending. You get a pulse output that represents actual volume passed.

The hardware is simple. Rotors, shafts, bearings, and a pickup. But the tolerances matter. We saw a lubricant blending plant in Malaysia improve batch consistency by replacing turbine meters with oval gear units. Because the liquid viscosity was around 120 cP, the turbine output drifted at low flow. The oval gear meter held its K-factor across the batch. A paint manufacturer in the Philippines used the same approach on a solvent line.

Fuel and Oil Applications Where These Meters Work

Diesel transfer from day tanks to generators is common in Southeast Asia, Africa, and the Middle East. A DN15 or DN20 oval gear meter fits well because the flow rates are small, often 2 to 20 liters per minute. The meter body can be aluminum with FKM seals for diesel. For heavy fuel oil, we normally recommend cast iron or stainless steel with PTFE seals because the temperature at the meter can reach 90 °C or more. A PT100 sensor option gives you a temperature signal over the same 4-20 mA HART loop.

Marine bunker fuel measurement is another area. Some customers in the Pacific Islands use a DN50 oval gear meter on a portable bunker skid. Flow range from 50 to 500 liters per minute covers small vessel fueling. The oil is filtered before the meter. An air eliminator is installed upstream. This protects the rotors from overspeed and incorrect volume counts caused by entrained air.

Hydraulic oil, gear oil, and lubricating oil skids also benefit. Because oils tend to have viscosity from 20 cP to over 1000 cP, positive displacement meters do not rely on turbulent flow profiles. Most engineers skip this part. They just want a pulse per liter or a 4-20 mA output to a batch controller. Our standard pickup gives a pulse resolution that matches many PLC high-speed counter inputs.

Model Selection and Technical Details

Silver Instruments supplies oval gear flow meters in sizes from DN15 to DN80. Standard accuracy is ±0.2 percent of reading and repeatability is ±0.03 percent. That repeatability is the reason a fuel terminal in Vietnam switched to our SGO series for diesel loading bays. The previous meter drifted after temperature changes. The SGO with aluminum body and FKM seals held stable output.

Body materials include aluminum, cast iron, and stainless steel. Aluminum works for clean diesel, gasoline, and light oils. Cast iron suits heavy fuel oil because it handles higher pressure and temperature. Stainless steel works when the fluid is corrosive or when food grade oil is involved. Seal options include FKM, PTFE, and EPDM. Do not guess the seal material. Send us the fluid name, temperature in °C, and viscosity in cP. We will confirm compatibility.

Output options include pulse, 4-20 mA HART, and Modbus. The HART version is useful when you need flow rate and total flow from one loop. Local display options include a mechanical totalizer or an LCD. For ATEX Zo