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Silicone Oil Flow Meter High-Viscosity Damping Optimization
Quick Answer: For silicone oil with viscosity above 500 cP the most stable measurement comes from a Coriolis mass flow meter with enhanced digital damping. The built in damping algorithm filters out pulsation noise without slowing down the response time. Silver Instruments SLW series with a custom damping coefficient handles 1000 to 100 000 cP silicone oil in DN10 to DN50 lines directly.
Why High Viscosity Silicone Oil Creates Measurement Noise
Silicone oil often runs at 350 cP 1000 cP or even 10 000 cP in chemical batching and heat transfer loops. In a positive displacement pump the flow is naturally pulsating. A flow meter installed close to a gear pump or a piston pump sees rapid pressure spikes. With high viscosity fluid the pressure waves do not dampen out fast. The sensor picks up hydraulic vibration. This shows as flickering readings on the transmitter display.
We saw this on a customer site in Thailand. A paint manufacturer was batching silicone oil at 800 cP into a reactor. The previous turbine flow meter gave a reading that jumped between 18 kg/h and 42 kg/h within 3 seconds. The DCS control loop kept tripping on flow deviation. The root cause was not the meter accuracy. It was the absence of mechanical or electronic damping tuned for high viscosity.
How Digital Damping Works in a Coriolis Meter
A Coriolis meter measures mass flow directly. The sensor tubes vibrate at their natural frequency. When silicone oil flows through the tube the phase shift between inlet and outlet gives the mass flow rate. This raw signal has a high frequency component from pipe vibration and a low frequency component from pump pulsation. The transmitter applies a low pass filter. You can adjust the damping time constant typically from 0.2 seconds to 60 seconds. Most engineers skip this part and leave the default setting at 2 seconds. For 2000 cP silicone oil a 2 second damping is often not enough.
Silver Instruments SLW series has a Damping Optimization function. You enter the fluid viscosity in cP and the nominal pipe size DN. The transmitter calculates an initial filter coefficient. On a DN25 line with 1500 cP silicone oil the suggested damping is 5 seconds. We have tested this on a loop with a sinusoidal pump pulsation of 1 Hz. The mass flow totalizer stayed within 0.15 percent of the reference scale. Without damping optimization the error was 0.9 percent.
Why We Recommend Coriolis Over Oval Gear for Silicone Oil
Oval gear flow meters are common for high viscosity fluids. They work well up to 2000 cP. But silicone oil above 5000 cP causes a measurable pressure drop across the oval gears. The clearance between the rotor and the housing is tight. As viscosity rises the torque required to turn the gears increases. The meter can slow down or stop at low flow rates. We had a customer in Mexico who used an oval gear meter on 10 000 cP silicone oil. The meter ran fine for 6 months then the bearings seized because the silicone oil had no lubricity and the polymer particles accumulated.
A Coriolis meter has no moving parts in the flow path. The straight tube design in the SLW series handles 0 to 60 kg/h for DN15 and up to 6000 kg/h for DN50. The pressure drop is lower compared to oval gear at equivalent flow rates. For a 50 cP silicone oil the pressure drop is about 0.3 bar at 1000 kg/h on a DN25 Coriolis. An oval gear meter of the same size shows 0.8 bar. At 5000 cP the gap widens further.
Field Tuning with the HART Signal
The damping para
Because silicone oil batches are often heated, the meter body temperature rises. The SLW series works up to 150 degrees Celsius. No special insulation is needed. The remote transmitter option keeps the electronics away from the heat. For a marine silicone oil heating skid we supplied a DN40 SLW with remote transmitter and 10 seconds of damping. The installation was on a ship in Singapore. The flow signal goes into a PLC that controls the thermal oil valve. No communication errors in 14 months.
Concrete Specification Details
When you size a Coriolis meter for silicone oil do not just look at the flow rate. Provide the viscosity in cP at operating temperature. Silicone oil viscosity drops sharply with heat. At 25 degrees Celsius the viscosity might be 1000 cP. At 80 degrees Celsius it can drop to 100 cP. The meter span must cover the maximum flow at the lowest viscosity. The line size is often DN25 or DN40 for transfer lines. Process connection is usually DIN PN40 or ANSI 150 flange. Wetted parts are 316L stainless steel. The sensor is available with ATEX Zone 1 certification if the silicone oil is used in a solvent recovery area.
One thing we learned from a project in Vietnam. The customer specified a Coriolis meter for 5000 cP silicone oil. At 30 degrees Celsius the oil was thick like honey. The pump was a progressive cavity type. The flow meter performed well but the zero point drifted because the plant had air in the line after cleaning. We added a back pressure valve downstream. The meter must always run with a full tube. Two phase flow even a small bubble of nitrogen will cause a high reading. That is not a damping issue. That is a process issue.
FAQ
Which flow meter type handles silicone oil above 500 cP best?
Coriolis mass flow meter. For continuous duty above 5000 cP a straight tube Coriolis meter is preferred because it minimizes pressure drop and has no moving parts that can seize.
Does damping optimization affect the totalizer accuracy?
No. Damping only smooths the live flow display. The mass totalizer uses the undamped high speed raw signal. Silver Instruments meters maintain totalizer accuracy within 0.1 percent of rate regardless of the damping setting.
Can I use a magnetic flow meter for silicone oil?
No. Silicone oil is non conductive. A magnetic flow meter requires a fluid with a minimum conductivity of 5 microsiemens per centimeter. Silicone oil has zero conductivity.
What is the typical pipe size and connection for silicone oil flow?
DN15 to DN50 is common. Connections are DIN PN40 flange or tri clamp for sanitary grades. Always specify the flange standard and the nominal pressure when ordering.
How do I send a request for a silicone oil flow meter quote?
Send us your silicone oil viscosity in cP at operating temperature, the required pressure rating in bar, the temperature in degrees Celsius, the pipe size DN, and the flow range from minimum to maximum in kg/h. Our email is [email protected].
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