back-draft damper
A damper, 1 having blades which are actuated by gravity, permitting air to pass through them in one direction only.
General
General
General
back propping
The placing of timbers, usually set in a diagonal or oblique position, to hold a wall in place.
General
back shore
In raking shores, an outer member under a rider shore that temporarily supports the side of a building.
General
back siphonage
The flowing back of used, contaminated, or polluted water from a plumbing fixture or vessel into the pipe which feeds