Connecting 12" Main to Existing 12" Main

[mes11]

Have a project where they want to loop the water line from one street with a 12" line to a cul-de-sac with a 1o" line. The proposed water line will be 12". When tapping to the existing 12" line, is it easier/better to use a tapping sleeve and valve or shut the line down and install a 12"x12" tee?

 

[bimr]

It depends. How many shut off valves are there are where are the valves located? If you are just shutting off the water to a few residences, then shutting down the system is practical.

If the service area includes businesses such as hospitals, schools, etc. then it may not be practical.

That is something that you have to evaluate with your project.

Note that procedures for disinfection of the water main may take some time.

 

[jgailla]

You can't tap a 12" line with a 12" tap. In the past I have used an 8" tap with a reducer to 12" immediately after the tap.
If you can get away with shutting off the water it will be cheaper. Usually the utility company will decide if they will allow you to shut off the water.

 

[rconner]

While not promising cheap, it might even be possible to cut-in a full size, 12" tee if some water supply cannot be interrupted to critical areas by closing or inserting shut-off valves each side some distance away and then making temporary water otherwise available to any critical facilities as with temporary bypass or jumper pipe etc.

 

[certvino]

There is no doing 12" or larger taps. You will have to isolate section of the system and cut into the main installing a tee and mechanical/dresser couplings.

 

[jgailla]

certvino,
It's not accurate to say that a 12" tap can't be done. Taps up to 16" are commonly performed, although I've never had occasion to wet tap anything bigger than 16". Mueller has the sleeves up to 36".

I do have to back off my earlier statement that you can't tap a 12" into a 12". I should have said it's not good practice and there is a high risk of splitting the pipe.

Also remember to consider joint restraint or thrust blocks.

 

[msquared48]

If you need the 12" flow, you might consider using two 8" taps off the existing 12" going to a new 8,8,12 tee fitting.

Mike McCann, PE, SE (WA)

 

[jgailla]

msquared,
It's been a while, but if I remember correctly the 8" tap to 12" reducer only cost about 5 psi at 1500 gpm.
Two 8" taps and a tee could be almost as bad for head loss.

 

[msquared48]

I figured that, but was suggesting the two 8" taps if a 12" could not be done.

Mike McCann, PE, SE (WA)

 

[mes11]

Thanks guys. You touched on my concerns as far as tapping a 12" line with a 12" tap. I like the idea of using an 8" tap to a 12" reducer. The head loss seems reasonable and since it's creating a loop the pressure in both existing lines should still improve.