I plan on replacing all the copper in my house with a pex system. the hot and cold pex manifolds seem much more user friendly. the copper in my house seems crazy, spliced and diced running all around. I am wondering if I can delete the expansion tank, I am thinking that pex tubing expands as it is. if not, should the tank be before the manifold? Thanks
An expansion tank is only required when the water supply system has a backflow prevention device or check valve. The extra pressure caused by thermal expansion was apparently an issue in the home. I would strongly suggest that you include it in your new set up. Don't rely on the pex to expand and relieve the pressure. That could cause a pipe to rupture or a fitting to leak. Expansion tanks are typically installed in a "tee" at the cold water inlet for the water heater.
I would just leave the copper there if it is not giving you too many problems. I wouldn't say that pex is so much better than copper that making the switch is worth the time or expense even as a DIY. Steel or iron supply or drain lines are a different story but if they are functional I leave them alone too.