Your oxygen concentrators are probably medical? There’s no problem at all to travel with them. There are no security checks. You’ll be travelling on trains, not planes. The exception being Eurostar, with some secutainment before boarding and because of leavinge the Schengen-zone/EU. Just bring a medical certificate to be sure, but probably nobody will ask about it  on every other rail company than Eurostar.

PS. Eurail is the company that sells the passes, but doesn’t drive the trains itself.

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