Hi rbarto,
I trust all is well at the moment, I had a similar problem with a client in a remote outback laboratory. This fix is not factory recommended but it may get you by until you can afford a system upgrade or if you are too far from civilization as we were. Remove the offending pump head and piston from the magnetic coupler. Try to remove as much of the corrosion as possible from the coupler, this can be done with a very fine emery paper. Use a thin smear of acrylic adhesive, lab made or store brought will do (two pot araldite or similar). You do not want to gum up the mechanics, but you need the glue to be tacky enough to assist the magnetic coupler to retain the piston and prevent decoupling. Attached the piston and allow a couple of minutes for the surface to bond. Assemble the piston head and try to set the pump to normal operational flow with the appropriate column or backpressure restriction coil and monitor the system to insure the piston does not decouple. This fix worked for our remote client and has run for six months, long enough for him to afford a system upgrade as I stated earlier. If the piston continues to decouple you should approach your local Dionex service centre and talk to them about a replacement pump block, which at the end of the day might be a more sensible solution. Please remember the initial corrosion was probably cause by poor seal maintenance especially the back up seals. I would recommend replacing both pistons, primary and back up seals otherwise this problem will only re-occur again, compromising operational pressure consistency and prime of the pump. Remember this is a last resort fix for those in the bush with little funding and falls under the category of kill or cure, however as it stands the pump is a boat anchor by the sound of it and you probably have everything to gain and nothing to loose. All the best and keep me posted on your progress.
