Siemens Symphony/Harmony/Essenza: high helium boil-off after cold head work
What happened
After a cold head replacement (RGD swapped for SC10) the magnet's helium consumption went up and stayed high; in a similar case on another unit, the helium loss was traced to ice under the cold head after a poor recondenser installation.
What was checked
- Opened up and inspected under the cold head: adsorber condition, lines, traces of ice or carbon dust
- Checked how the head sits and its thermal contact with the radiation screens
- Tracked helium flow readings over time to see whether the boil-off was settling or staying high
Cause
Reported in the case: a regenerated (refurbished) adsorber was fitted to cut cost, and carbon from it got into the cold head; the head failed, so the high boil-off continued after the swap. In the second case the head was left open too long during a replacement by inexperienced hands, and ice formed under it and in the cryostat channel.
What was done
The engineers replaced the cold head (SC10 in place of the RGD) together with a new adsorber and the lines; in the ice case the system was de-iced and the head reinstalled with correct seating and contact. Both units then ran with normal helium consumption — the outcome is described as solved.
Safety
Treat the cryostat as a pressurised cryogenic vessel inside a permanent magnetic field: never block vent or relief lines, use only non-magnetic tools near the magnet, and leave the cryogenic circuit to authorised personnel following the manufacturer's procedures.
Lesson: A cold head swap is only as good as what surrounds it — a cheap regenerated adsorber or a slow, unskilled install can kill the new head and cost a full set of parts again.
Covered in the course: MRI Service — Level 2: Fault-Finding →
Written from an anonymised case shared by service engineers. It is not a manufacturer instruction and grants no authorisation. Independent note; names are trademarks of their owners.