I have seen many instances where valves are down sized from the pipe size and have inquired - there always is an answer which usually involves some hydraulic issue: such as headloss, velocity, scouring, etc etc.
Well that's the screwy part Bob - not only did we downsize from 18" RCP to 16" DIP there was a rubber one way check valve behind the gate valve. One of these -
https://www.procoproducts.com/product-category/check-valve-manufacturers/
Not only did they choke the pipe down on a storm line but what happens when the valve gets plugged up with dip bottles, potato chip bags, etc? Since this is located in the loading dock and "star" tour bus area there is no telling what sort of debris will make it into the trench 60' long trench drain and 3 grate inlets that feed this check valve.
Well here's a learning lesson that we already knew to do but just didn't do it...
The vault was 14' deep with a bottom middle riser and top. We had very detailed shop drawings that I checked prior to casting which checked out on the money. So the crew sets the box, riser and top. Specs called for Conseal and water plug on the joints and black mastic rolled on the outside for "waterproofing."
A final grade check on the top of the vault shows it's sitting .17' or 2" too high. The crew goes to check the flow line - within .02' which was a relief. Well it turns out the riser was .17' too tall. Get on the horn with my supplier and they casted a new one which the crew swapped out.
If this vault had been out in the parking lot we might have been able to make the grade work. However this vault is 6-8' from the loading dock edge that has a 1/4" per FT slope away from the building. The edge of the dock would've been lower than the top of the vault.
Moral - even though you have good detailed shop drawings always check what's been delivered first.
