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Positive Displacement Flow Meter for Oil: High-Viscosity Petroleum Gauges
Quick Answer: A positive displacement flow meter is the most reliable choice for high-viscosity petroleum oils because each gear rotation captures a fixed volume, not fluid velocity. Silver Instruments oval gear PD meters measure heavy crude, fuel oil, and lubricants from 2 cP to 100,000 cP at 0.5% of reading. For a quote, send oil type, viscosity at 40 °C, pipe size DN, pressure in bar, and minimum flow rate in L/h.
Most turbine and electromagnetic flow meters struggle when oil viscosity climbs above 50 cP. A positive displacement meter does not rely on Reynolds number. The chamber and oval gears trap a fixed volume. Every gear rotation equals a known volume. Viscosity changes from 50 cP to 5,000 cP have almost no effect on accuracy. Refineries and fuel oil terminals continue to use PD meters for custody transfer and internal allocation because of this behavior.
Why Positive Displacement Works for High-Viscosity Petroleum
Crude oil, bunker fuel, bitumen, and heavy lubricants often range from 100 cP to 50,000 cP at process temperature. At these levels, flow profile is not uniform. A velocity-based meter such as an electromagnetic flow meter cannot measure non-conductive oil. A turbine meter can read oil, but its K factor shifts when viscosity changes. A positive displacement meter avoids that problem. The chamber volume is fixed. Output pulses come directly from gear rotation. Total volume repeatability stays within 0.1% to 0.3% in many oil applications.
In practice, a PD meter for oil needs one thing. The oil must be clean enough to prevent gear wear. We specify a strainer or filter upstream. For crude oil with wax or sand, a 200 mesh strainer is common. For clean fuel oil or lubricating oil, 100 mesh is enough.
Specs That Matter for Crude Oil and Heavy Fuel Oil
Silver Instruments supplies oval gear PD flow meters in sizes from DN4 to DN100. Standard flow ranges cover 0.5 L/h up to 50,000 L/h depending on viscosity and pipe size. Here are the specifications our customers ask for most:
Flow range: 0.5 to 50,000 L/h
Accuracy: ±0.5% of reading for oil from 10 cP to 2,000 cP, ±0.2% optional
Viscosity range: 2 cP to 100,000 cP
Pressure rating: PN16 standard, PN40 and PN63 optional
Temperature rating: -30 °C to 180 °C standard, 250 °C with high temperature gears
Output: pulse, 4-20 mA, HART, Modbus RTU
Wetted parts: cast steel, 316 stainless steel, aluminum, PPS gear with PTFE seal options
Hazardous area: ATEX Zone 1 and Zone 2 versions for petroleum storage and refining
Do not assume one size fits all. A high viscosity oil needs a larger clearance or a slower gear speed. A fuel oil distributor in Vietnam installed a DN25 oval gear meter for 1,000 L/h of 380 cSt fuel oil at 60 °C. That DN25 unit worked, but the pressure drop was 0.8 bar. A DN40 meter reduced pressure drop to 0.25 bar and extended gear life. That is the kind of detail you can only catch in sizing, not in a catalog.
Oval Gear PD Flow Meter from Silver Instruments
Our standard product for petroleum is the SIOG series oval gear flow meter. The body can be aluminum for fuel oil or 316 stainless steel for crude oil, diesel, and light lubricants. For high-temperature bitumen and heavy crude, we use cast steel with carbon graphite bearings. Pulse output works with batch controllers. The 4-20 mA HART version connects to PLC systems in terminals and refineries. Some eng
We also supply a high-viscosity version with a built-in gear reducer and larger ports. For example, a customer in Oman meters heavy crude at 25,000 cP and 80 °C. The SIOG-40-HV unit with DN40 flanges and PTFE seals handles 1,200 L/h at 0.45% accuracy. This meter has run for 18 months with one gear inspection. No major wear was found.
Installation Notes for Refinery and Terminal Sites
PD meters need a straight run, but not as long as turbine or ultrasonic meters. We recommend 5 DN upstream and 3 DN downstream. Install a strainer directly before the meter. For heavy oil above 1,000 cP, keep the meter warm with steam tracing or electrical heat tape. Cold spots create wax deposits. That causes gears to stick and readings to drift low.
Do not run a PD meter dry. The gears rely on oil as a lubricant. Air slugs in a loading arm cause over-speed and mechanical damage. Install an air eliminator or a back-pressure valve if the line has intermittent flow. We see this often in truck loading racks where hoses drain between batches.
What to Send for a Quote
Because we size every oil meter case by case, we need specific process data. Silver Automation Instruments is a flow meter manufacturer and supplier for positive displacement oil meters. Send us the following at Tel: +86-135-1213-1526 or Whatsapp: 86-135-12131526:
Oil type and viscosity at operating temperature in cP
Flow range in L/h or m³/h
Pipe size DN and pressure rating
Temperature in °C
Output signal needed: pulse, 4-20 mA HART, or Modbus RTU
Hazardous area classification if required
If you have a current meter that drifts or jams, include a photo and a short description. Our engineers can often identify the problem before quoting a replacement. We serve customers in Southeast Asia, Oceania, Latin America, Africa, and the Middle East. You can also reach us on WeChat at +86 13512131526.
FAQ
Can a positive displacement flow meter measure heavy fuel oil with 380 cSt viscosity?
Yes. A PD meter handles 380 cSt fuel oil without loss of accuracy. Choose a larger meter size to keep pressure drop below 0.5 bar and use a strainer upstream.
What is the typical accuracy for high-viscosity crude oil?
Most Silver Instruments PD oil meters achieve ±0.5% of reading. For custody transfer or blending applications, we can supply ±0.2% of reading with factory calibration.
Can the same meter measure diesel and heavy crude oil?
It is possible if the viscosity range stays within the gear clearance limits. But for a wide range from 3 cP diesel to 25,000 cP heavy crude, we often recommend two meter sizes or a high-viscosity version. You avoid gear wear and pressure drop problems.
Do these meters need a straight run upstream?
A straight run of 5 DN upstream and 3 DN downstream is enough for most oil services. PD meters are not sensitive to flow profile like turbine or ultrasonic meters.
ATEX Zone 1 certification for petroleum terminals?
Yes. Silver Instruments offers ATEX Zone 1 and Zone 2 versions for oval gear PD meters used in refinery, fuel oil, and crude oil storage areas. Ex d and Ex ia protection methods are available depending on output type.
Contact Silver Automation Instruments today. Send your oil type, viscosity, flow range, and pipe size to get a proper PD flow meter quote.