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Fischer Porter Flow Meter Troubleshooting: Fixing Float Stickiness in Variable Area Meters
Quick Answer: Float stickiness in a Fischer Porter variable area flow meter is usually caused by dirt, coating, gas bubbles, or a worn float guide. Clean the tube and float first, verify vertical mounting, and inspect the guide rod. If the problem continues, send us your fluid type, flow range, pipe size (DN), pressure (bar), and temperature (°C) for a replacement or repair recommendation.
Common Causes of Float Stickiness
Most Fischer Porter variable area meters are simple devices. A float moves inside a vertical metering tube. Stickiness means the float does not move smoothly when flow starts or changes. In many field cases the cause is not the meter itself. It is the process fluid or the installation.
We have seen these causes on customer sites in Southeast Asia, the Middle East, and Australia. Dirty water with sand or rust particles. Sticky chemicals such as glucose syrup, latex, or heavy fuel oil. Gas bubbles entering the meter from a pump suction leak. A bent float guide after a pressure spike. Scale or polymer coating on the glass or metal tube. Horizontal mounting where vertical is required. Excessive pipe vibration from a nearby pump.
Step 1: Remove the Meter Safely
Close the isolation valves. Vent the line and drain the meter. Wear chemical gloves if the fluid is acid, caustic, or solvent. For a DN15 to DN50 Fischer Porter meter, this usually takes less than 30 minutes. If the meter carries an ATEX Zone 1 nameplate, follow site permit rules before opening the housing.
Step 2: Inspect the Tube and Float
Remove the inlet or outlet fitting. Take out the float assembly carefully. Do not drop the float. A scratched float or tube changes the calibration.
Here is the thing. A thin layer of oil or scale is enough to cause float stickiness at low flow. In one case a paint manufacturer in Vietnam had a Fischer Porter meter on a solvent line. The float would not lift until flow reached 35 percent of full scale. The cause was a dry coating on the stainless steel float. A soft brush and isopropyl alcohol removed the coating. The meter returned to normal within one hour.
Step 3: Clean Without Damaging the Tube
Use warm water and a non abrasive detergent for organic fouling. For scale, use a weak citric acid solution. Do not use wire brushes on the metering tube. Do not use strong acid on a glass tube. For metal tube Fischer Porter meters, check the chemical compatibility table before cleaning.
If the float has a PTFE or Hastelloy body, avoid strong solvents that can swell or pit the surface. Dry the parts with compressed air at low pressure.
Step 4: Check Alignment and Installation
Fischer Porter variable area meters are designed for vertical mounting with flow from bottom to top. A small tilt of 5 degrees can cause the float to touch the tube wall. Use a spirit level on the inlet and outlet flanges. Correct the pipe alignment before you reinstall the meter.
Most engineers skip the alignment check after cleaning. That is a mistake. Vibration also creates stickiness and false readings. If the meter is near a pump, install flexible hoses or pipe supports. We have seen a water treatment plant in Malaysia where vibration from a dosing pump caused the float to jump at low flow. Adding isolation pads fixed the problem.
Step 5: Check the Float Guide and Magnetic Coupling
Some Fischer Porter models have a guide rod inside the tube. A bent guide rod will stop the float at the same position every time. Replace the guide rod if it shows wear or curvature.
Metal tube variable area meters may use a magnetic coupling from the float to the indicator. If the floa
Step 6: Reassemble and Test
Install the float with the sharp edge or flow arrow facing upstream. Reinstall the gaskets. Tighten the fittings evenly. Open the isolation valves slowly. Check for leaks at the tube and process connections.
Run the meter from zero flow to full flow and back down again. The float should move smoothly without sticking. If it still sticks at low flow, check the fluid viscosity. High viscosity liquids above 100 cP often need a larger meter size or a different float design.
When to Replace the Float or Tube
Replace the float if you see deep scratches, dents, or chemical attack. Replace the tube if the glass is cracked, cloudy, or etched. Do not try to polish a glass metering tube. The internal diameter determines the calibration. Polishing changes the ID and ruins the accuracy.
For a DN15 to DN100 Fischer Porter variable area meter, replacement floats and tubes are available from Silver Automation Instruments. Send us the model code, serial number, and a photo of the parts.
Model Specific Notes for Fischer Porter Meters
Many older Fischer Porter variable area meters in oil and gas, water, and food plants are still in service. Common sizes range from DN15 to DN100. Accuracy is typically plus or minus 2 percent of full scale for liquids and plus or minus 3 percent for gases. Process connections may be flanged, threaded, or sanitary tri clamp. Some units have a 4-20 mA HART transmitter for remote flow totalization.
When ordering spare parts, specify the tube material, float material, and scale range. For example, a DN25 meter for diesel at 50 to 500 litres per hour needs a different float than a DN25 meter for water at 200 to 2000 litres per hour.
Get Replacement Parts or a New Flow Meter
If the float still sticks after cleaning and alignment checks, contact Silver Automation Instruments. Tell us the fluid name, viscosity (cP), flow range, pressure (bar), temperature (°C), and pipe size (DN). We can supply replacement glass tubes, floats, guide rods, and complete variable area flow meters.
Tel: +86-25-68650347
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FAQ: Fischer Porter Float Stickiness
1. Why does my Fischer Porter float stick only at low flow?
Low flow stickiness is usually caused by dirt, oil film, or scale on the tube wall. Clean the tube and float first. If the fluid is viscous, check whether the meter is sized for the actual flow range.
2. Can I use a solvent to clean the glass tube?
Yes, but use a solvent that is compatible with glass, the float material, and the gaskets. Do not use wire brushes. Dry the parts fully before reassembly.
3. Does horizontal mounting cause float stickiness?
Yes. Most Fischer Porter variable area meters require vertical mounting with upward flow. A tilted or horizontal installation makes the float drag against the tube or guide rod.
4. How do I know if the float or tube needs replacement?
Replace the float if it is scratched, bent, or corroded. Replace the tube if it is cracked, etched, or cloudy. If the tube ID has changed due to deposits or scratches, calibration may be off.
5. Can Silver Automation Instruments supply Fischer Porter compatible parts?
Yes. We supply replacement floats, tubes, guide rods, and complete variable area meters for many Fischer Porter models. Send us the model code, serial number, fluid type, and flow range for a quote.
Visit flow-meter.com.au for variable area flow meters and spare parts. For fast support, send your application data to Silver Automation Instruments.
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