SLOW DOWN TANK

[whizza]

I am looking for details re a slow down tank. The tank is used when a force main (pumped line) is fed into a gravitational sewer system. Anyone?

 

[bimr]

Unless your force main is discharging at greater than 6.5 feet/sec, you don't need to bother with any special design.

The usual practice is to align the crown of the force main with the crown of the sewer at the receiving manhole. If the receiving sewer is substantially lower, add a drop inlet to the manhole.

 

[whizza]

Thank you. Just one thing should it not be the invert of the force main aligned with the crown of sewer?

 

[bimr]

One common method of minimizing turbulence (and liberation of hydrogen sulfide) is to align the crown of the force main outlet with the crown of the sewer at the receiving end. The invert of the manhole would then be sloped smoothlly between the force main and sewer invert.