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Wedge Flow Meters and Differential Pressure Flow Meters: Resilient Geometry for Highly Viscous Slurries

Quick Answer: Wedge flow meters and differential pressure flow meters handle highly viscous slurries because the resilient wedge geometry has no dead pocket and resists solids settling. For sludge, starch, pulp stock, and mining tailings, a wedge element plus a DP transmitter gives repeatable 4-20 mA HART output. Send your pipe size in DN, viscosity in cP, pressure in bar, temperature in °C, and flow range to Silver Automation Instruments for a quote.

Most engineers who work with slurries have seen a full-bore meter fail. Electrode coats on electromagnetic flow meters. Gears jam in oval gear flow meters. Coriolis meters can be accurate but pressure drop in a large slurry line can stop the process. Wedge flow meters are different because the restriction is off to one side and the flow path stays open.

Why Wedge Flow Meters Handle Highly Viscous Slurries

A wedge flow meter uses a V-shaped wedge welded into the pipe or machined into the meter body. The wedge creates a controlled pressure drop. A DP transmitter reads the high and low side pressures and converts the signal to flow. The wedge ratio, often 0.3 or 0.5, sets the measuring range. Because the wedge sits in the lower half of the pipe, the liquid sweeps past the restriction without a dead zone.

Highly viscous slurry behaves more like paste than water. At 8,000 cP or 15,000 cP, solids do not stay suspended in the same way. We have seen a starch processor in Thailand run a DN80 wedge meter on a 12,000 cP starch slurry. The line ran for more than two years with remote seals and no regular cleaning. A standard orifice plate would plug in days.

Differential Pressure Transmitter Setup for Slurry Lines

Direct impulse lines are a weak point on any DP flow meter in slurry service. Thick slurry can block the small pressure taps. For highly viscous material, use a DP transmitter with remote seals and capillary lines. The seals mount flush to the process connection so solids cannot pack into the impulse line. Silver Instruments supplies the SI-DP differential pressure transmitter with 4-20 mA HART output and optional ATEX Zone 1 approval. The transmitter can be paired with a PT100 sensor for temperature compensation.

A DP transmitter measures the pressure difference across the wedge. Flow is proportional to the square root of the DP. Most HART transmitters can output a square root signal directly. If the slurry has changing density, take a regular sample to correct the totalizer. For a wastewater plant in Australia, a DN100 wedge flow meter with a 0 to 50 kPa DP range was sized for 40 m3/h. The HART signal carried flow, DP, and temperature on one pair of wires.

Specifying the Right Wedge Flow Meter

Start with pipe size and flow range. Wedge flow meters are available from DN15 up to DN600 and larger on request. The wedge ratio and DP range depend on viscosity, solids content, and pressure drop budget. For high viscosity, a wider wedge gap or lower DP range keeps pressure loss manageable. For low flow, a smaller gap improves resolution.

Wetted materials are 316L stainless steel as standard. Hastelloy C276 is available for corrosive slurry. Remote seal diaphragms can be 316L, Hastelloy, or tantalum. Flanged connections are common in DN50 and above. Wafer designs fit between flanges and save space.

Here is the thing. Do not only look at the flow element. The transmitter, remote seals, and installation location decide whether the meter works for more than a few months. We have seen customers in Southeast Asia buy a wedge element with a low-cost DP transmitter and direct impulse lines. The meter read wrong after two weeks because the impulse lines clogged. Remote seals are not optional for most highly viscous slurries.

Customer Cases and Industry Fit

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