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Rosemount Magmeters and Rosemount 8705 Series: Flanged Electromagnetic Flow Instruments

Quick Answer: The Rosemount 8705 Series is a flanged electromagnetic flow meter for water, wastewater, chemical, and slurry lines. Silver Automation Instruments builds a direct replacement with the same face to face dimensions, liner options, and 4-20 mA HART output at a lower price. Send your pipe size (DN), flow range, pressure (bar), and temperature (°C) to get a quote for a DN15 to DN600 replacement.

What the Rosemount 8705 Series Covers

Rosemount magmeters in the 8705 line are designed for process and utility lines. The flow tube is flanged and available in sizes from DN15 to DN900. Common liner materials are PTFE, PFA, and hard rubber. Electrode options include 316L stainless steel, Hastelloy C, titanium, and tantalum.

The meter handles clean water, wastewater, acids, caustics, and slurries with solid content up to 30 percent. Conductivity must stay above 5 µS/cm for a stable reading. For water and wastewater plants this is rarely a problem. For deionized water or pure solvents a magmeter will not work.

Why Engineers Replace the 8705 with a Silver Automation Instruments Meter

Price is usually the main driver. A Rosemount 8705 with a 8712 transmitter costs more than many project budgets allow. Silver Automation Instruments offers a flanged electromagnetic flow meter that matches the process connection and output signals. The meter body is welded and pressure tested to EN 1092-1 or ASME B16.5 flange standards. The transmitter supports 4-20 mA HART, pulse, and RS485 Modbus.

We have seen this on customer sites many times. A wastewater plant in Chile needed six DN150 flanged magmeters for sludge return lines. The Rosemount 8705 delivery time was 8 weeks. Our replacement shipped in 3 weeks. The meters measured 0 to 400 m3/h with an accuracy of 0.5 percent of reading.

Key Specifications for the 8705 Series Replacement

You should check liner and electrode compatibility before you order. PTFE liner is common for chemicals and high temperature streams. Hard rubber is common for water and wastewater. PFA liner covers high vacuum and aggressive acids. Electrode material depends on the process fluid. 316L works for water and weak chemicals. Hastelloy C works for acids. Titanium works for seawater and brine. Tantalum works for hydrochloric acid service.

Process pressure ratings are PN10, PN16, PN40, and ASME 150 lb. Fluid temperature can range from -20 °C to 150 °C depending on the liner. The transmitter has a local display and can be remote mounted if the pipe runs in a high vibration area. For hazardous areas, ATEX Zone 1 and Zone 2 approvals are available on request.

Common outputs are 4-20 mA HART, pulse, and RS485 Modbus. Some projects also need a PT100 temperature input for heat metering. We can supply that option. The minimum conductivity for standard electrodes is 5 µS/cm. For low conductivity fluids above 0.5 µS/cm you need a special capacitive electrode design.

Sizing and Installation Notes

Most engineers select a magmeter size that matches the pipe diameter. The flow velocity should stay between 0.3 m/s and 10 m/s for stable accuracy. For abrasive slurries keep velocity below 3 m/s to protect the liner. For clean water you can run 5 m/s without a problem.

Installation is straightforward. You need a straight run of 5 pipe diameters upstream and 3 pipe diameters downstream. The meter must be full of liquid at all times. Gas bubbles cause reading errors. Never install a magmeter at the highest point of a pipe where air collects. A paint manufacturer in Southeast Asia learned this after installing a meter on a vertical line with downward flow. The meter lost signal when the pipe was not full. We moved the meter to a horizontal section and the reading became stable.

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