These are more walls than they are elements, but whatever:
1. One Way Wall (ONWA)
This wall works much like a check valve, only allowing particles to pass through the wall in one direction (once they pass through, they cannot return). The only direction that the particles can pass through will be set by Line Tool (much like fan)
Uses: anywhere you need to prevent backflow, such as high pressure machines
2. Nuclear wall (NUCW)
This wall works much like the powder wall, liquid wall, and gas wall. It only allows nuclear elements, and by modifying its TMP value, allows only certain nuclear elements
Uses: anywhere you need to keep nuclear elements (or just certain ones) in and/or out.
#1 there is still that nasty backflow problem...
Can't think of a use for an elements-only wall
Well, only if you time the E-hole right...