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Replacing the Impedance

\item {\bf HOW OFTEN:} As needed.
\item {\bf SYSTEM STATUS:} Cans fully removed.

To clean the impedance, you first need to evacuate the mixture from the lines for a LONG time. Pump on both sides of the dilution unit by opening V6. Once you have collected all of the mixture into the dumps, make a note of the pressure in the dumps, then close all valves.

You will need:


  1. Collect the mixture for a long time (2 days is sufficient). Pump on the circuit with the turbo, forepump, compressor ON, and V4, V5, V6, V7, V8, V11, and V12 OPEN. The rest closed.
  2. Close all automatic valves. Turn all pumps off.
  3. Make a note of the pressure in the dumps.
  4. Close V13, V14, and V11.
  5. Get a pony bottle of ultrapure helium, and attach a regulator and adaptor to KF fittings.
  6. Set the regulator, so that the maximum pressure is 3-4 PSI. Flow helium through the lines to clear the lines of other gasses.
  7. Attach the bottle of pure He to the external valve attachment, V10.
  8. Open V6.
  9. Once the bottle is attached, slowly begin to leak helium into the system.
  10. Watch the turbo pressure, P3. Make sure that the pressure doesn't go too far above 1 bar, as this can damage the system.
  11. Keeping the pressure slightly above 1 atm, remove the old impedance by loosening the bolts on either side.
  12. Put the new impedance in place with new stainless steel gaskets and tighten it down.
  13. Close V10, and remove the helium bottle.
  14. Attach the red pumping cart to V10. And vacuum out the lines using the roughing pump. Then turn the roughing pump off.
  15. Open V10, and begin pumping on the system again. When the pressure gets low enough, turn on the turbo, and pump on the system for an hour.
  16. Close V10. Turn off and remove the pump cart.

Now to leak check the new impedance, close and evacuate the OVC with the red pump cart. Attach the leak checker, and leak check the OVC. Once the OVC passes the leak check, perform a throughput test while watching the leak rate, ([sec:tests.throughput]see §sec:tests.throughput). If you see a leak while performing the throughput test, it must be coming from the impedance, quickly collect the mixture, open the OVC and tighten the impedance. If the impedance passes the throughput test, perform the test again at 10K.

next up previous contents
Next: Servicing the KNF compressor Up: Maintenance Previous: A Full Scrub   Contents
Jonathan Ouellet 2014-08-26