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Posted: Sun Nov 28, 2010 7:38 pm
by wantalc
had a result last week a building inspector let me put a back drop on the out side of a existing manhole.it was justabout imposible to put it inside the chamber...he let me use a junction on the rocker pipe 
normaly i hate doing back drops but this one was a doddle...any one else on here hates doing back drops or is it just me....
Posted: Sun Nov 28, 2010 7:51 pm
by lutonlagerlout
i think we call the same thing a tumble
rather than make the fall too steep we sometimes have a vertical section of pipe say 600MM onto a rest bend into the manhole
great time saver
LLL 
Posted: Sun Nov 28, 2010 9:21 pm
by seanandruby
Can't understand why you hate doing a backdrop ??? They can save a lot of unnecessary excavation. If the gradient is going to be less than 1/10 you are allowed to use them. You would , in most circumstances put them outside the manhole. Did one last week 225 timesaver, very heavy, but used a deadman to hold the bend.
Posted: Sun Nov 28, 2010 10:03 pm
by GB_Groundworks
We call them drop shafts and are dead common, always outside the manhole and continue the run into the man hole for roding purposes. Drops down to invert level and into the run.
Posted: Tue Nov 30, 2010 11:52 am
by Tony McC
There's a cross-section drawing of a typical drop-shaft connection here
Edited By Tony McC on 1291117955