Schedule 40/80 vs C900 water pipe 2

[655321]

On private commercial project, say a school campus, where the water lines are privately owned and maintained:

Would you spec out 4" pvc domestic supply waterline as schedule 40/80 or would you use a C900 (PC-???) pipe? Is there an advantage at this size to one over the other, fittings, gasket joints vs glue, etc.

Also about pressure rating, what's typical for service lines? I've seen clear criteria for public mains (which varies, some cities want all the public mains DIP PC350, others are less worried about it). But there's not much guidance I found for private services lines. Does the plumbing code indicate a minimum pressure class?

Thanks in advance for our help.

 

[655321]

Your help. Thanks in advance for your help.

 

[coloeng]

You first need to determine what pressure class pipe you should use. The best way to do this is find out what is the maximum operating pressure for the water supply to the school campus, then add a factor of safety for surges, etc.

The type of pipe is more of an organizational/personal preference. Sch 40/80 PVC is typically easier to install than gasketed pipe, mainly because the fittings are all glue joint. The glue joints also provide a restrained system, unless you have really high pressures, you don't typically need to provide thrust restraint at bends and tees. Our experience with glue joint pipe has been that it will eventually start leaking, not sure if this is because the pipe is restrained and the expansion/contraction eventually weakens the joints, or if the pipe and glues they used in the 70s and 80s wasn't very good. If you use ductile iron mechanical joint fittings instead of glued fittings, you have to use a different size of gasket than what is typically supplied with the bolts and glands and you have to provide some type of thrust restraint.

C900 pipe is designed to be the same OD as the same size ductile iron pipe and has gasketed joints. The advantage to having the same OD as ductile iron is that the pipe fits into the ductile iron fittings without having to have special gaskets. Gasketed joints does not provide a restrained system so thrust restraints at bends, tees, deadends, etc. is more critical. Gasketed joints are also typically quicker to install than glue joint, although we have found that the crew that installs it needs a little more knowledge than a crew that installs glue joint pipe.

Sch 40 PVC is typically less expensive than C900. Sch 80 PVC is about the same cost as C900.

In our water system we specify C900/905 for any pipe 4" and larger up to 14".

Hope this helps.

 

[alexcmmi]

Pressure rating is your difference. As stated above:

Sch 40/80 PVC is same OD as steel pipe
C900 is same OD as DI pipe.

You will get higher pressure rating from the C900. C900 has surge allowance factor of 2 built in.

See unibell.org for all PVC pipe questions - the are the DIPRA of plastic pipe

Pressure rating for service lines is 100% dependant on the system you are operating in. You could have 25 psi at the delivery point or you could have 100 psi - kinda depends where you are on the muni systems HGL. If you have dedicated, well supply, well, you should know exactly what pressure your are at.

For 'convenience' purposes (aesthetics of feel I suppose), water should be delivered between 25-40 psi at fixtures.

 

[655321]

Hey thanks a lot both of you.

Coloeng,I talked with a contractor who said the same thing about leaking on large diameter schedule pipe. He recommended using C900 pipe with Ductile Iron fittings and thrust blocks, he doesn't like any of the PVC fiting options.

Do smaller diameter PVC lines tend to leak over time?

 

[semo]

I agree that anything 2" or larger, I would not use glue joints.

I don't think the problem is with the glue or the plastic; but, with quality control during construction. It doesn't take much to swab plenty of glue on a 1" or 1 1/2" pipe and know that the pipe will fuse to the fitting. A 4" pipe has a lot of surface area to swab and if the glue dries before you get the fitting and pipe connected or you don't get enough glue on the fitting, you won't get a good bond. That will haunt you later.

I would as mentioned look at the pressure rating you need. Probably go with a Class 160 or 200 pipe. If you don't have a lot of fittings the gasketed pipe will also install quicker than having all of those glued joints.

I will disagree that Sch40 is less expensive. The wall thickness is higher for Sch 40 than for Class 200 so there is more plastic (ie more cost). Whoever supplies the pipe will be able to supply the correct gaskets and glands for the fittings if they know the pipe you are connecting them to.

 

[coloeng]

We've only had problems with glued pipe 4" and greater. Before I got here about 15 years ago, they used to use glued pipe up to 8" OD. I think we have replaced all of it because it began having leakage problems.

 

[bimr]

The recommended pipe joint for underground piping applications is a flexible joint. The flexible joints will allow movements of the piping without causing leaks.

PVC piping with glued joints is not generally recommended because the joints are rigid and will break when the ground moves.

 

[LUDPEKA1]

The civil firm that I use to work for, had a general rule that glued under ground joints were not aloud no matter what the line size was. For the same reasons stated by "bimr".

 

[rconner]

There are a great many issues to consider in the selection of pipes and joints, including performance, safety, and other aspects. Some of these have been discussed on this thread. Others are discussed in many other threads (and linked references therein) like

http://eng-tips.com/viewthread.cfm?qid=227506

and

http://eng-tips.com/viewthread.cfm?qid=217072.

 

[655321]

Another sort of related question while were at it:

I know how public mains are disinfected and tested. But what about private service lines?

I don't believe I have ever scene seen any notes on our's or other's site plans regarding it. Is that part of the plumbing code?

 

[bimr]

The building's plumbing system (after the water meter) must meet the minimum bacteriological standards as set forth by the State Health and Safety Code (Department of Public Health). The building owner is responsible.

http://www.cp.berkeley.edu/cds_ucb/Appendix-I.html