Very simple question
Very simple question
(OP)
I do not remember the main reasons why we match crown to crown on storm drain pipes. I was asked today and I am drawing a blank. Anyone know why.
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS Come Join Us!Are you an
Engineering professional? Join Eng-Tips Forums!
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail. Posting GuidelinesJobs |
|
RE: Very simple question
RE: Very simple question
RE: Very simple question
1. To compensate for headlosses within the structure.
2. To maintain a uniform HGL and reduce the opportunity for a hydraulic jump within the structure.
3. Just because - its the way we have done it for years.
RE: Very simple question
Way back, in this case means, back to the time of Newton, Bernoulli (can't remember which Bernoulli), Manning and a few others of that ilk.
good luck
RE: Very simple question
Set the criteria and then design to it. If you match invert to invert then you are not meeting the design criteria. .
RE: Very simple question
One reason was to match the HGL but the main reason was to reduce the turbulence of combining flows to reduce the production of H2S & consequence of acid attack on the system below the junction.
I assume that in drainage systems, the requirement is to match the HGL.
RE: Very simple question
If inverts are matched there will be less turbulence.
The HGL in the larger downstream pipe will be higher than the HGL in the upstream pipe creating a backwater in the upstream pipe.
The velocity in the upstream pipe will be less than design.
The upstream pipe may in fact flow full
Because the velocity in the upstream pipe is less there is less turbulence at the junction. However, for pipers laid to minimum grade the self cleansing velocity will not be achieved and theoretically there will be settlement in the upstream.
setting crown to crown (HGL to HGL) gives flow through the junction without a drop or without a backwater. That is why it is done.
RE: Very simple question
When a smaller sewer joins a larger one, the invert of the larger sewer should be sufficiently lower to maintain the energy gradient. An approximate method for securing this result is to place the 0.8 depth point of both sewers at the same elevation.
Flow Channel:
The flow channel through manholes should be made to conform in shape and slope to that of the sewers. A bench should be provided that should have a minimum slope of 2 inches per foot.