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Asphalt Flow Meter 2 Inch: Hot Mix Facility Integration Best Practices
Quick Answer: For a 2-inch (DN50) asphalt flow meter in a hot mix plant, choose a jacketed positive displacement meter, typically an oval gear type. The meter body must stay above 135°C using hot oil or steam tracing. Silver Automation Instruments supplies oval gear meters with integrated heating chambers, high-temperature sensors, and 4-20 mA HART output, pre-configured for bitumen batching and blending.
Integrating a flow meter into a hot mix asphalt facility is not like standard fuel or water metering. You are handling bitumen at 150 to 190°C, with viscosities often above 500 cP. A mistake in meter selection leads to seizing, pressure drop, or bad batch ratios. We have replaced meters for two separate asphalt plants in Indonesia and Thailand that installed bare-body oval gear meters without heat tracing. They seized within three weeks.
Here is the thing. Most engineers know the meter must handle high temperature. But they overlook the need for constant heat across the meter body, flanges, and even the impulse lines. Cold spots cause asphalt to set, blocking the gear rotation. When you order a 2-inch oval gear meter for bitumen, you need full jacket coverage. Silver Instruments oval gear flow meters for hot mix asphalt come with a cast heating chamber that wraps the measuring chamber. The jacket uses hot oil or steam at 0.4 to 0.6 MPa. This keeps the internal temperature uniform and avoids thermal shock when hot bitumen first enters the meter.
Why a Jacketed 2-Inch Oval Gear Meter Fits Hot Mix Plants
The 2-inch (DN50) size matches the batch cycle and flow rates of typical asphalt batch plants that produce 80 to 160 tonnes per hour. During the injection phase, the bitumen flow rate often sits between 2 and 15 m³/h. An oval gear meter with a pulse output gives the batching controller a precise volume total at the right speed. Because the meter turns at 1 to 120 pulses per litre, the PLC can stop the injection valve at exactly 0.1% repeatability. Coriolis meters work, but for bitumen batching the cost and electrical setup are overkill compared to a simple jacketed oval gear meter.
We have also tested electromagnetic flow meters on bitumen. They fail. Bitumen is non-conductive, so the electrode gets no signal. Vortex meters clog and become a solid block after shutdown if heat tracing fails. Oval gear meters with positive displacement are the practical choice. They do not need conductivity, they tolerate particles up to 100 microns with hardened gears, and the pressure drop stays around 0.2 to 0.5 bar at rated flow.
One customer, a road construction contractor in Malaysia, ordered three DN50 oval gear meters with hot oil jackets and PT100 temperature probes two years ago. Their biggest fear was meter damage during maintenance shutdowns. We suggested adding a manual bypass with a steam-out port on the meter. They confirmed the meters still run 24 months later with no repair, just biannual seal replacement. This detail matters because asphalt meter life often ends during cleaning, not during daily use.
Best Practices for Integration into Hot Mix Control Systems
Connect the flow meter signal into the batching PLC. Use a 4-20 mA HART transmitter with pulse output as backup. The HART signal lets you check the meter health, coil temperature, and jacket temperature remotely. Most batch house operators ignore diagnostics until a bad batch appears. With HART, the PLC or a field calibrator can read the meter body temperature. If it drops below 130°C, do not start the batch. This simple interlock saves you thousands in remixing and rejected loads.
Install the meter on the discharge side of the bitumen pump, not the suction side. On the suction side, vapor bubbles cause inaccuracies and gear chatter. Keep straight pipe runs short, DN50 meters need only 2D upstream with installed strainer. Locate the meter as close to the injection nozzle as practical to reduce thermal lag in the piping. Insulate the connecting pipe and jacket line together. Many installers wrap the meter in thermal cladding and forget the flanges. Then asphalt freezes at the flange gap and blocks the inlet. Cover everything, flanges included.
For batch accuracy, use a high-resolution pickup. Standard reed switch outputs give 1 pulse per litre on DN50 oval gear meters. For hot mix batching where bitumen ratios are critical, we recommend a hall-effect sensor with 10 to 100 pulses per litre. The finer resol
During shutdown, flush the meter with hot bitumen or use a purge valve to drain the chamber. Do not let the meter cool with asphalt inside. If you cannot flush, keep the jacket heating active for at least 30 minutes after the last batch. A temperature-controlled electric heater on the jacket can serve as a backup for steam plants that shut down at night.
What Silver Instruments Supplies for DN50 Asphalt Metering
We build oval gear flow meters in 316L stainless steel with hard chrome-plated rotors for asphalt service. The 2-inch model comes with a standard ASME B16.5 Class 150 or 300 raised-face flange. The jacket is a carbon steel shell welded to the meter body, with NPT threaded connections for hot oil. You give us your hot oil temperature and pressure, we confirm the jacket thickness. Standard transmitter is a high-temp PT100 resistance thermometer inserted into the meter body and a 4-20 mA HART board mounted remotely. In some cases, customers request a local indicator without transmitter for simple plants. We supply both.
Typical items in the quotation: jacketed oval gear meter DN50, flow range 1 to 18 m³/h, max 200°C, accuracy ±0.5% of reading, mating DIN or ANSI flanges, PT100 with transmitters, pair of connection cables, and factory calibration certificate traceable to ISO 17025. We also include a set of Viton or PTFE seals depending on your bitumen additives.
Because every plant has slightly different pipe layout, send us a simple sketch with your bitumen temperature, working pressure, pipe size, and required flow range. We size the meter and jacket for you. Ordering a jacketed meter off-the-shelf is risky. We have seen cases where the jacket nozzle clashes with support beams or platforms. One Philippine customer ordered a meter from Europe with the jacket port on the wrong side. They had to re-orient the meter with complex piping. Our team provides a dimension drawing before production so you can check the fit on your skid.
FAQ
Can I use a 2-inch flow meter for polymer-modified bitumen (PMB)?
Yes, but the meter internals need hardened gears and seals compatible with polymers. Silver Instruments oval gear meters for PMB use tungsten carbide bearings and PTFE seals. You also need to keep the temperature above 165°C and reduce the flow rate by 20% to handle higher viscosity.
What output signal does the asphalt flow meter provide?
The standard unit provides a pulse output from a hall sensor (10 to 100 pulses per litre) plus an optional 4-20 mA HART analog output. Most batching PLCs prefer pulse for totalizing. Use the 4-20 mA signal for temperature compensation or jacket monitoring. Both signals are active simultaneously.
How often do I need to recalibrate a bitumen oval gear meter?
Under normal conditions with daily cleaning, calibrate once per year. If you process PMB or abrasive fillers, recalibrate every 6 months. The calibration is simple with a master meter or weigh tank. Silver Instruments offers a calibration adapter fitting that lets you run a field check without removing the meter from the line.
Do I need a filter or strainer upstream of the meter?
Always install a Y-type strainer with mesh size 40 (0.4 mm) immediately upstream. Bitumen tanks can contain carbonized lumps that jam gear meters. A strainer protects the meter and extends seal life. Silver Instruments supplies a strainer with a blow-down valve as a set with the meter.
Can the 2-inch meter handle start-stop batching duty cycle?
Yes, oval gear meters are well-suited for intermittent batching. The design does not need a steady-state flow. You can start and stop the hot bitumen flow many times per hour. Just ensure the jacket heat stays constant to prevent thermal cycling stress. We have tested our meters to 20,000 start-stop cycles in our factory with bitumen simulant.
Send us your bitumen temperature in °C, working pressure in bar, pipe size (DN), and flow range in m³/h. We will return a specific quotation with a dimension drawing within two working days. See our oval gear flow meter page for standard datasheets and images.
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