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Cleaning the 4K Trap


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

Cleaning the 4K trap will involve dropping the full shields. Strictly speaking, the 4K trap sits at about 40K and is there to filter any boil off from the 77K trap. This trap should empty when the system warms, and shouldn't need to be cleaned. But if you are going to clean it, follow this procedure. Begin with all automatic valves closed.

  1. Dismount the lower half of the OVC, the 70K and the 4K shields. If you have no reason to remove the still shield, you can leave it in place. To do this, simply reverse the process laid out in [sec:prepare.mounting.ovc]§3.2.5 and [sec:prepare.mounting.shields]§3.2.4.

  2. Remove the top half of each shield. This is done exactly like the lower halves, but must be done after, so that the shields have clearance. Make sure to set the top half of each shield gently on top of its lower half, and not on the floor.

  3. Make sure that the 77K trap is attached and cold.

  4. Open manual valves V11 and V12.

  5. Open automatic valves V1 and V5. (V2, V3, V4, V6, V7, V8, and V9 should be closed).

  6. Turn on the condenser and fore pump.

  7. Locate the 4K trap. See photo.

  8. Using a heat gun, carefully heat the 4K trap for a period of 15-20 minutes. The 4K trap should be just slightly too hot to touch. USE CAUTION: Close to the 4K trap are many wires which don't respond well to excessive heat.

  9. Replace the top half of the shields. [CITATION]

  10. Replace the bottom half of the shields. [sec:prepare.mounting]See §3.2.

  11. Clean the 77K trap. [sec:maint.clean77trap]See §7.2.


next up previous contents
Next: Scrubbing the Mixture Up: Maintenance Previous: Cleaning the 70K Trap   Contents
Jonathan Ouellet 2014-08-26