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Oil Tank Truck Flow Meter Integration: Positive Displacement Meters for Custody Transfer
Quick Answer: For oil tank truck custody transfer, positive displacement meters give direct volume measurement that holds accuracy during short batch loading. A DN50 oval gear meter with pulse output, 4-20 mA HART, and ATEX Zone 1 approval is a common choice for diesel and fuel oil loading skids. Silver Automation Instruments supplies these meters with ISO 17025 calibration certificates for fuel depots in Southeast Asia, the Middle East, Latin America, and Africa.
Positive displacement meters work well on truck loading because the process is start-stop. A fixed volume passes through the meter for each rotor cycle. Air slugs, fast closing valves, and short loading batches do not reduce repeatability the way they can with velocity-based meters.
Why Positive Displacement Meters Work for Oil Tank Truck Loading
An oval gear positive displacement meter uses two oval rotors that rotate inside a precision housing. Each rotation sweeps a known volume from the inlet to the outlet. The output is directly proportional to the number of rotations. This direct measurement principle suits custody transfer for diesel, gasoline, kerosene, and light fuel oils.
Most engineers skip this part: a turbine meter may perform well on a continuous pipeline, but tank truck loading is a batch process. Short flow intervals, pump start and stop, and trapped air create unstable flow conditions. A positive displacement meter creates a physical seal between the inlet and outlet, so the measurement stays stable.
We have seen this on customer sites many times. A fuel distributor in Vietnam replaced a turbine meter with a DN40 oval gear meter for 30,000 liter truck compartments. The repeatability improved to better than 0.2 percent on the same loading arm. A customer in the Philippines uses a DN50 aluminum oval gear meter for diesel delivery at 200 to 350 L/min and reports stable pulse output at the batch controller.
Key Selection Parameters for Tank Truck Custody Transfer
Start with the pump curve and loading target. A standard diesel loading pump often delivers 200 to 400 L/min. A DN40 oval gear meter covers 5 to 250 L/min. A DN50 covers 80 to 500 L/min. Silver Automation Instruments recommends DN50 for fleets that load above 250 L/min and DN40 for smaller trucks with a 5,000 to 15,000 liter capacity.
Pressure rating matters at truck loading bays. Most systems run between 4 bar and 10 bar at the meter inlet. We specify PN16 flanges as a minimum. Some terminals in the Middle East run higher differential pressure during simultaneous loading. In those cases PN25 or PN40 is safer. Body material options include aluminum for diesel and gasoline, cast steel for heavy fuel oil, and stainless steel for aggressive or high purity fuels.
Temperature is another practical issue. Diesel in hot climates such as Oman or the Philippines can reach 45 °C inside the loading line. Our standard oval gear meters handle -20 °C to 120 °C. For gasoline, the fluid is lighter and more volatile. Use aluminum bodies with PPS rotors to reduce rotating mass and avoid ignition risk in ATEX Zone 1 areas.
Integration with Loading Skids and Batch Controllers
A standard truck loading skid has a pump, air eliminator, strainer, positive displacement meter, control valve, and loading arm. The meter should sit downstream of the air eliminator and strainer. Air before the meter causes false volume. A strainer protects the oval gears from pipe scale, weld slag, and foreign material after maintenance.
For custody transfer, you need at least one pulse output. Many batch controllers and loading computers accept a quadrature or single channel pulse input. Silver Automation Instruments oval gear meters can be supplied with a dual channel reed switch, NPN open collector, or 4-20 mA HART transmitter. A mechanical totalizer on the meter body gives local verification without power.
Here is a common integration: a DN50 aluminum oval gear meter with pulse ou
Calibration and Custody Transfer Approvals
Custody transfer is a legal measurement in many countries. That means the meter should have a traceable calibration certificate. Silver Automation Instruments supplies each positive displacement meter with a calibration certificate from our flow rig. We can also arrange ISO/IEC 17025 calibration for critical truck loading depots.
Some end users in the Middle East and Africa ask for Weights and Measures pattern approval. Check your local regulation before purchase. In practice, a calibrated oval gear meter with repeatability of 0.1 percent or better passes most depot audits. Keep the calibration certificate on file for each meter serial number.
Because PD meters are mechanical, calibration can drift if the fluid has abrasive particles. This is why a strainer is mandatory upstream. We recommend 60 mesh for diesel and 100 mesh for gasoline. Inspect the strainer every month during peak season. Replace the mesh if the pressure drop increases by more than 0.3 bar.
Recommended Meter Configuration for Diesel and Fuel Oils
A practical custody transfer configuration for diesel tank trucks is a DN50 oval gear flow meter with an aluminum or stainless steel body. Meter size DN50. Accuracy plus or minus 0.2 percent of reading. Flow range 80 to 500 L/min. Process connection DN50 PN16 flanges. Outputs: pulse and 4-20 mA HART. Local display: mechanical totalizer. Hazardous area: ATEX Zone 1 or Zone 2 according to site classification.
For heavy fuel oil or hot bitumen, choose a cast steel body with stainless steel rotors and PTFE seals. Viscosity up to 1000 cP is acceptable for most oval gear designs. We have supplied similar meters to a paint manufacturer in Southeast Asia for solvent loading and to a marine fuel supplier in Chile for IFO 180.
Frequently Asked Questions
1. Can a positive displacement meter handle diesel and gasoline on the same truck?
Yes, but the wetted materials must match both fluids. Aluminum with PPS rotors works for diesel and gasoline. Do not use the same meter for water because water has low lubricity and can accelerate rotor wear.
2. What is the typical accuracy for tank truck custody transfer?
Most positive displacement meters from Silver Automation Instruments achieve plus or minus 0.2 percent of reading. Repeatability is usually 0.1 percent or better. This is suitable for depot truck loading when combined with a traceable calibration certificate.
3. Does the meter need an air eliminator?
Yes. Air or vapor in the fuel line creates false volume. Install an air eliminator upstream of the positive displacement meter. The air eliminator must be sized for the same flow range as the meter.
4. Which output signal should I send to a loading computer?
Use a pulse output for the loading computer. A 4-20 mA HART signal goes to the PLC or remote monitoring system. Many terminals use pulse for batch control and analog for flow rate display.
5. How do I request a quote from Silver Automation Instruments?
Send us your fluid type, viscosity in cP, flow range in L/min, pressure in bar, temperature in °C, pipe size in DN, and the required output signal. Our sales team will reply with a model recommendation and price. Contact Tel: +86-25-68650347, WhatsApp: +86-25-52155837, WeChat: +86 15365082610.
For a tank truck custody transfer flow meter quote, send your pump flow rate, viscosity, pressure rating, and hazardous area classification. We can supply bare meters, calibrated meters, or complete loading skid instrumentation packages. Contact Silver Automation Instruments at Tel: +86-25-68650347, WhatsApp: +86-25-52155837, WeChat: +86 15365082610.