“Illustrated Encyclopedia of Building Services
…
small-bore heating system
A pump-assisted domestic-size installation employing 12.5 mm and 19 mm bore copper or thin bore special mild steel pipe distribution. The collecting headers at the boiler are usually of larger bore. It operates best as a dosed system. It employs a canned rotor circulator to meet the head (resistance) requirement. Each sub-circuit must be valved to permit balancing of the circuits and to avoid the short-circuiting of water around the circuits with the least resistance.”
( https://books.google.rs/books?id=oXouqsmEcdkC&pg=PA276&lpg=P... )


KudoZ (Serbo-Croat to English translations [PRO]):
cevni razvod > pipe distribution
( http://www.proz.com/kudoz/serbo_croat_to_english/other/32222... )