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Maintaining Sample Flow for Analyzers: Key Components and Troubleshooting Tips

Learn how to ensure constant sample flow for analyzers with tips on back pressure regulators, flow control valves, strainers, and cooling systems.

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Maintaining Sample Flow for Analyzers: Key Components and Troubleshooting Tips

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  1. Keep Your Samples Flowing or Where can an analyzer get a drink around here? David Webster P.E. Solutions, Inc.

  2. Acknowledgements Bob Ricker – Sentry Equipment Carl Trantham – Nevada Power Leonard Zeedyk – Nevada Power Billie Rea – FPL Energy

  3. The goal is to get each analyzer a drink of water at constant flow and 25°C

  4. Sampling 101 • The “Constant Pressure Header” is one key

  5. The “Constant Pressure Header” requires a reliable back pressure regulator/relief valve

  6. The design of a reliable Back Pressure/Relief Valve (BPRV) has large internal orifices, high flow capacity, and does not plug easily.

  7. This type of Back Pressure Regulator plugs up easily and the adjustment knob is confusing. It should be set and left alone, but because it plugs up, the lab techs have to stroke it to try to clear out the debris. Also, the diaphragms tend to break easily.

  8. This panel at a plant in Colorado has the BP valve handles removed so no bad adjustments can be made Notice that your new BP/RV’s cannot be adjusted!

  9. The BPRV acts as a “shock absorber” and a safety valve

  10. A good BP/RV has a “flat” performance curve, which means that it will relieve a lot of flow and still keep the back pressure constant.

  11. Do not restrict the BP/RV outlet to the sink!

  12. Sampling 101 • The flow control valve is the second key

  13. Rod-in-tube valve design Use when pressure >500 psi Needle valve Use when pressure <500 psi The two main types of sample flow control valves are selected based on sample pressure

  14. The rod-in-tube valve design breaks down Main Steam or Boiler Drum pressure without wire drawing the seat. (Because there is no seat!)

  15. The BP/RV and Flow Control Valve work together to provide a Constant Pressure Header

  16. The rod-in-tube valve design relies on small annular clearances between the rod and the tube which can plug up easily with debris & magnetite.

  17. Solutions, Inc SDS-15-SS A high capacity strainer will protect the VREL from debris entrained in the sample. Boiler Drum samples are usually the worst offenders

  18. The new strainer has 15 times more surface area than the usual sample strainers (Nupro-Swagelok) . 15 in2 strainer surface area These strainers have approx 1 in2 of surface area.

  19. Our new strainer design uses an integral blowoff port. When used with a high pressure ball type blowoff valve, this is a reliable way to keep the strainer element clean without requiring disassembly.

  20. Blow the strainer down frequently (more during start-ups.)

  21. How can I tell if my constant pressure header is working?

  22. The gauges will all read the same (BPRV setpoint), the rotameters will stay steady, and there will be ADEQUATE FLOW TO THE SINK

  23. The pressure gauges all read the same.

  24. The rotameters stay steady

  25. There is adequate flow to the sink

  26. How do I troubleshoot low sample flow, or if I can’t get 20 psi? • Stroke the VREL to clear debris (40 turns full open to full close). • Clean the Nupro Filters • Look for excess flow going to an analyzer • Check the BPRV diaphragm for a pinhole leak (weeping out the hole).

  27. The Cooling System • Your new system relies on “lots of flow” through the coolers to control temperature • If you can hear the tubing rattle, throttle the flow on the top valve a little, just until the rattling stops.

  28. All Sample Coolers are not created equal Double Helix coolers have more surface area and therefore the sample temperature “approaches” the cooling water temperature more closely Many coolers do not have “coil-in-coil” (double helix) and the cooling surface area is not sufficient to give a good “approach temperature”

  29. The chiller will maintain 77 ºF within 1 degree.

  30. Some data for Lab folks • Sample velocity of 6’/second is optimum per EPRI.

  31. Sample Lag Time Flow rate Velocity Tube Size cc/min Ft/sec Lag Time/1000’ 1/4”x.049” wall 500 2.5 6.5 min 12006.02.8 min 3/8”x.065”wall 500 0.9 18.7 min 1200 2.2 7.6 min 16663.05.6 min Theoretically correct > 3300 6.0 2.8 min But not practical 1/2”x.125 wall essentially equal to 3/8”x.065 wall 6.0 ft/sec is approximately 1.8 m/sec

  32. Erosion/Deposition and Equilibrium

  33. Velocity vs. Deposition

  34. Deposition vs. Time

  35. Handling magnetite & debris • Keep velocity up to 6’/sec (1200-1800 cc/min target) • Keep sample flowing to the sink for “cushion” • Blow down dirty samples frequently (Boiler Drum)

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