Sanitary Force Mains 3

[GoldDredger]

A collegue came to me with a question regarding sanitary force main construction. They are designing an 8" main from a lift station. Along the way, the force main dips into a low spot then climbs back out towards it's destination. He asked if any provisions for sediment accumulation at the low spot should be made.

We both got a laugh at the thought of installing a blow off valve at the low spot.

I don't think any provisions are needed. It would be cost prohibitive to transition to gravity, then another pump station at the low spot.

I thought I would check here and see if anyone has an opinion.

 

[bimr]

Solids do not settle out if the velocity in the force main is a minimum of 2 ft/sec.

Solids do settle out at lower velocities or when the pump is stopped and a velocity of 3.5 ft/sec or greater is then required to resuspend the deposited solids.

A small to medium size pumping station with pumping intermittently, the desirable force main velocity would be 3.5 to 5 ft/sec.