In an emergency situation like this one, the patent owner company wouldn't risk a huge PR loss by suing or even complaining, but when the crisis will be over they might decide to act. However, if those valves are reverse engineered, copied and given away without selling them, there would be no profit. That should fall into fair use.
I think there's something 100% valid in what you're suggesting, but it seems there's a fair bit of confusion here.
"Fair use" is a copyright thing, not a patent thing. I don't actually know if a widget (whether patented, patent expired, or never-patented) is covered by copyright - and even if it is, at least from what I know about copyright in music/literature, "fair use" wouldn't allow for making 100% complete working copies.
"not for profit" doesn't fly as a defence against either copyright or patent infringement in other areas, I suspect it wouldn't here either.
I'm reasonably sure if the "owner" of these valves started making noises about overly onerous enforcement of any patent/copyright that applies, and sane government would step in and declare some emergency-use legal exception for cases like this.
I wonder if the "owner" could make some obvious olive-branch offer along the lines of:
"Hey, that's our widget you're printing, but we totally understand that for the duration we were unable to get our version into your hands for reasons outside both our and your control. Normally we earn $x per widget when you source them through the usual channels, we are happy to waive that for the duration of the supply chain disruption, but ask that once things are back to normal, you continue to support the research and development that goes into those and other life saving products we make, and start buying from the usual supply chain, or paying our regular royalty on locally printed versions. Thanks, WidgetCompany"
