You need at least 2D of straight pipeline (for nq<50). To be on safe side instal one or two ribs in the elbow. The end of the rib has to be sharpened in non symmetrically way at the outlet in order to prevent creation of any vortices (so called »Karman vortex street«).http://www.turboinstitut.si/
Rubber is more used to avoid abrasion. Problem is also piping.
try/search for water conditioner (maybe magnetic water treatment)
www.carefree.com.au/page/industrial.html
www.hop-pth.co.il
http://www.turboinstitut.si