I was just wondering what people's thoughts were on building/retrofitting pools with schedule 40 vs 80 PVC since I had a near disaster on my hands today when a piece of schedule 40 connecting a drain valve to a T-joint on the main drain line (basement surge tank) broke off while i was closing the valve (slowly, of course)
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When considering schedule 40 vs schedule 80 be sure to take the pipe ID (inside diameter) into account. On average schedule 80 has approximately 8% smaller i.d. That can be significant when you approach the flow maximums for a specific pipe size. Max flow through a 2.5" sch 40 pipe would require a 3" sch 80 pipe to handle the same flow.
For example the i.d of a 2.5" sch 40 pipe is a nominal 2.445"
The i.d. of a 2.5" sch 80 pipe is a nominal 2.29"
This reduces the flow capacity by about 8%. This becomes an issue to consider when approaching the high end flow capacity of a sch 40 pipe, or when considering flow velocities (which are significantly higher in schedule 80).
The 2 products are not a direct swap fro each other and of course this adds to the cost factor as well.
I like schedule 80 for pool wall penetrations, pump nipples, and a stress locations. Used in minimal lengths the TDH increase is slight and the flow minimally affected, but if using it for the entire run, be sure to do your calcs. because you may have unintended flow problems.
Use a multipurpose or transition glue
Rob M said:
I love schedule 80 pipe. You can't kill it. I always offer it to my customers as an upgrade for below grade pipe and fittings. It is also important to use sch. 80 glue and PRIMER, not cleaner. The sch. 80 glue has more solids in it and is gray, not blue. When you are calculating the job, make sure that you use a "Schedule 80 Friction / Flow chart." The thicker wall of the sch. 80 means that it carries less water than sch. 40 of the same size.
On a giant job, one of my guys was digging a plumbing trench wiht a mini-excavator and had been fighting rocks all day. He hooked a 2" pipe that was stubbed out the back of a 24" wide beam. The bucket tooth dug into the pipe and the pipe did NOT break. I cut the pipe 3" from the beam and installed a coupling. The day was saved because of the material choice of the engineer. If the pipe had cracked, it would have been very expensive to repair.
I like sch. 80 because it is so tough. Pressure is not an issue on swimming pools. Really guys, are we ever oner 100 PSI?
A good PVC blue joint is actually a solvent weld. When I see failures of the pipe and fitting to weld it usually not enough priming (particulary on dirty pipe) or the square cut pipe scrapes away the glue when it is pushed into the fitting. Chamfering the end of the pipe helps avoid this. When it comes to Sch.80 PVC another fact comes in to play: all manufacturers do not have the same outside diameter on their pipe and inside diameter on their fittings. The difference is small but when the pipe is 'fat' and the socket is 'skinny' the solvent can be squeezed out when you push th pipe in. Conversely, if the pipe is 'skinny' and the socket is 'fat' a loose fit is the result, but this can be overcome by using heavy-body glue and laying it on thick. This situation happens when you use 6" (and larger) Sch.40 pipe and insert it into Sch. 80 flanges - quite a common situation on commercial filter systems.
Back to the original question: I don't see any reason to use Sch.80 pipe unless high pressure or chance of impact or other stresses is likely. Just be double careful to get a good solvent weld connection in critical locations.
First, let me state that my areas of expertise is residential, and NOT COMERCIAL. That said, if you are putting in comercial installations, disregard this post adn seek out someone with 25 years of comercial experiance or more.
I never use anything less than schedule 40, and after over 25 years in the field, my views have not changed. I have seen no benefit from using thicker gauge pipe and fittings. Sometimes the stiffer the pipe, the harder it is to make a good connection, as you cannot bend the pipe as easilly. While classified 200 is way to thin and breaks way to easilly, 80 is a lot harder to work with. If you have ANY bend in the pipe where it connects to the fitting, you'll pay a price with 80 that you won't usually have to pay with 40. Like I said, for me, the benefits of stronger pipe are almost always offset by initial cost and hasstle in installation of the thicker pipes.
Prime, prime and then prime again. Small pipe sizes, especially sch 40 with fast set glues are usually never a problem. Once you start hitting sch 80 4" and bigger you need to start holding that joint together a while as they will always try to pop apart for a bit. Getting into 10" and 12" its a good idea to have a clamping system in place.
If you have ever spent any time trying to remove a pipe from a fitting or valve, it is easy to see if it was primed well or not. It is VERY difficult to get one apart that has been scrubbed well with primer. The ones that are simply glued can almost be pulled apart.
This is the first job in as long as i can remember where the glued joints came apart, and the only difference was the Sch.80.
When we looked at the fittings they did not appear to be "welded" together like you get when you use primer and a good quality glue on Sch.40. It seemed like the density of the pipe did not allow the primer or glue to penetrate the PVC and therefore the only thing holding the fitting together was the dry glue itself...
Adding a few Sch.80 fittings upstream of the pump is not a bad idea. We actually upsize our plumbing to 3" immediately after the pump to minimize the velocity, and thus significantly reduce the pressure in the pipes...
I personally don't see the benefit of using Sch.80 on main drains... that line would be under vacuum, and you would be hard pressed to colapse a Sch.40 pipe with even the largest of pumps.
Instead of worying about the internal pressure, and using Sch.80, why don't you go up a pipe size or 2... It will cost about the same as using Sch.80 (maybe even less) and you will end up with a dramatically more efficient system that costs less to run, and will last longer in the long run as well.
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