What type of pipe to use?

[StoneCold]

I have an old gravity sewer line that runs 215ft to a sewer manhole.
The existing line is a 4" clay tile and the city engineer would like me to replace it/ upgrade the line. The line currently services an industrial facility with about 100 people. The pump that empties the lift station into the sewer line is a 1.5hp submersible pump, that pumps about 100 gpm. A camera view of the existing line shows that other than some sludge it is in pretty good shape. To appieze the town engineer we are looking at shoving a pipe inside the line to act as a new line without digging up the street. My sewer contractor would like to use sch 40 pvc in 20ft sticks. The town engineer would like us to use 2.5" sch 40 pvc. I am not crazy about the pvc choice. I would rather go with 2" continuous polyethylene if we could make that work.
What pipe size and material would you suggest?

Thanks for your thoughts.

StoneCold

 

[bimr]

Slip lining Contractors typically want a difference of 2" in diameter between the pipe and liner to make the installation easier. 2 inch pvc has an OD of 2.375" so it will be a tight fit. Not sure if you could get a Contractor willing to install 2.5"

Many Contractors do not want to line pipe less than 6 inches because of the tight clearances. There are other lining methods but many of them do not line pipes less than a 4 inch liner.

The most common type of liner used for lateral rehabilitation is CIPP.

http://www.lateralliners.com/default.asp?fn=benefits

Typically there are local Contractors that specialize in lateral lining. Recommend that you use a Contractor that does this type of work every day.

 

[cvg]

you might consider pipe bursting to install a new line. 100 gpm is a bit much for 2 inch line, especially since you say it is gravity. I would never use anything less than 4 inch for a gravity sewer.

 

[dicksewerrat]

Why is the Town Engr. wanting you to replace the line? Is the City doing something to the existing main line? Can he prove your line is failed? Causing the city a problem? Apparently this guy doesn't have enough things to keep him busy.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[StoneCold]

The existing line is gravity per say, but we are pumping into it and it just happens to run down hill. I think the pressure drop in the line will be about 15psi minus the recovery from running down hill. Lining is big bucks about$13k. Boring a new line and pulling in new pipe is about $6k. I think sliding in the new 2" will be about $2k even the new 3" poly or 2.5" poly if I could get it would be in that neighborhood. And no road cut.

We will see what I can work out with the town engineer to put this to bed.

Regards
StoneCold

 

[redbridge]

I think the 2" continuous polyethylene would be better. I have never heard of a 1.5 hp pump that would pump 100 gpm. I would do some research on the pump and see where on the curve the pump will operate with the 2" continuous polyethylene. If you can show the town engineer that the pump will run on the curve and provide enough flow then he or she should be fine with it.

 

[bimr]

The head loss for 215 feet of PE pipe at 100 gpm is 36.4 feet. Disregard elevation because no change in elevation.

Brake HP = (gpm * head)/(3960 * pump efficiency)

= (100 * 36.4)/(3906 * 62.5%)

= 1.47 HP

 

[redbridge]

bimr,

You are right. I am just used to higher head applications.

 

[StoneCold]

We are probably running the 3" poly line because the city engineer will not allow me to run a velocity higher than 5ft/sec. It will work out fine if we do a road bore. I just want to get it finished and get on with other projects.
Luckily it was hovering around -10F last week so the ground should be good and frozen to add a little challenge to the project.

Thanks for the input.

StoneCold

 

[StoneCold]

Just a note to finish this thread off.
We installed a 4" 200 psi rated Polypropylene line using a bursting head and hydraulically pulling it from the manhole in the street. The pump is puttting out about 65 gpm. Turns out the actuall installation had about 5 more 90's than the drawing to make everything line up. However the flowrate is good enough. It is not pumping dry and re-starting all the time, and it does not fill the lift station up above the inlet, so all is good.

Regards
Stonecold.