Plumbing Question: Rigid PVC vs Flex PVC

[TKpoolOH]

I am trying to open a can of worms here because I just can't understand this. If rigid PVC is so superior to flexible PVC (when both are schedule 40) why do half of the builders in my area use flex PVC? They're not fly by night builders either, these are reputable builders that have been doing it a long time. In my area the soil is all clay. Termites/insects aren't problem, but you never know what pests or an infestation might show up.

I get that rigid PVC is the superior product for it's durability and longevity. It seems this is the only one someone will actually recommend (people don't recommend flex apparently from what I can find). I can also see how having to do so many connections (if not properly or even improperly) could lend to potential leaks.

I get all the negative things I've seen about flexible PVC: potential insect/termite damage, potential crushing from compaction/backfill/cement/soil weight, etc., and how the ridges on the inside of the pipe can affect flow, and sharp rocks/objects can damage it. I also get how using as much continuous pipe as possible eliminates potential leak points and while you never want the ground to move, flex PVC is probably better than rigid if it does.

Can some of the pros on this site help answer this question for me once and for all? This is the last hold up for me to get started on my pool build here in 2021!

 

[jimmythegreek]

I use flex at times only when I have to. I heat bend if I can, but ridgid is superior amd the finish product is too. Most installs w flex are around spas amd main drain feeds to aid in curves. Ridgid is more stable if ground moves actually the pressure is spread out where flex will do just that, but in a small spot. I'm OCD with plumbing I hate to see flex on the pad amd being used for curves instead of quality pipe fitting work. Ridgid just takes more abuse on a jobsite and 20ft lengths leave few fittings.
Older pools are plumbed with poly sprinkler pipe amd many are still working as is today. It's a regional and preference issue as well as time. PBs that plumb their own pools may use flex but i haven't seen am actual plumber do so yet. Mayne repair work but not am actual new install

 

[TKpoolOH]

Thank you @jimmythegreek I really appreciate the insight. I completely get being OCD with the plumbing. I'd much rather spend more time/money to make sure it's done properly than save a few bucks, even if just a small difference in the superiority of rigid vs flex. I want to know the pool/plumbing will last as long as possible.

My previous pool at my old home used that poly sprinkler pipe you mentioned, of course it was built around 1980. All the PBs I've talked to do their own plumbing, don't subcontract out to plumbers, so your comment on that sounds spot on (1/2 do flex, 1/2 do rigid).

@jimmythegreek follow up question: Would you be able to provide any guess/estimate as to longevity of rigid vs flex? (ie. expect rigid to last 50 years, flex to last 40 years) I of course know you can never predict cracks/leaks/problems/etc.

 

[jimmythegreek]

I really cant speculate I haven't been around that long. I have dug up PVC from the 80s amd it was in good shape still. I haven't dug much flex its not popular around here. Some that was 15 to 20yrs old was in good shape as well. I just dont have the confidence in it like ridgid. I'm a belt amd suspenders guy, I charge a premium amd I deliver like it's my own home pool

 

[TKpoolOH]

I really cant speculate I haven't been around that long. I have dug up PVC from the 80s amd it was in good shape still. I haven't dug much flex its not popular around here. Some that was 15 to 20yrs old was in good shape as well. I just dont have the confidence in it like ridgid. I'm a belt amd suspenders guy, I charge a premium amd I deliver like it's my own home pool

I completely understand, thanks for the insight!

 

[sktn77a]

If rigid PVC is so superior to flexible PVC (when both are schedule 40) why do half of the builders in my area use flex PVC? They're not fly by night builders either, these are reputable builders that have been doing it a long time. In my area the soil is all clay.

I'm not a pool builder but I do have a pool. I also see all kinds of trade activities where reputable(?) companies take the path of least resistance (especially if they are under pressure to meet a budget or deadline). I don't know the answer to your question but my in-laws have a pool built in 1964 with rigid Sch40 PVC pipe and they've never had a leak. I have a 25 year old pool with rigid Sch40 PVC pipe that has never had an issue. Now that's just an "n of 2" but I'd probably want to stick with rigid pipe

 

[TKpoolOH]

I'm not a pool builder but I do have a pool. I also see all kinds of trade activities where reputable(?) companies take the path of least resistance (especially if they are under pressure to meet a budget or deadline). I don't know the answer to your question but my in-laws have a pool built in 1964 with rigid Sch40 PVC pipe and they've never had a leak. I have a 25 year old pool with rigid Sch40 PVC pipe that has never had an issue. Now that's just an "n of 2" but I'd probably want to stick with rigid pipe

Thanks Keith, definitely makes sense to stick with rigid!

 

[MMTech24]

I’m in the process of re-plumbing my pad and changing to a new VS pump. Just purchased the house last year. Previous owners got all new pool decking (stamped concrete) and replaced all plumbing at the same time in 2005. All plumbing was done in flex pvc 1.5”. I’ll post more when complete but here what it looks like. Pretty bad for 16yrs old. The return to pool line is much darker color compared to suction lines. I’m thinking it’s due to the granular chlorine feeder on the pump pad. Suction lines actually look OK. So I decided to dig back until the pipe goes under the concrete and just replace what I can while I’m at it.

 

[jimmythegreek]

The lines jacket absorbs whatever soil type its buried in and stains. As long as you dont have termites in your area ot should be fine. I've seen many pools with poly sprinkler lines amd they are 40yrs old and still running strong, flex is a step up from that

 

[coolviper777]

I am also in the process of replacing the entire skimmer suction line to the pump and the return line. They were the white flexible type 1.5" lines. The actual lines were ok, but they were a patch work of barbed fittings under ground, and they failed the pressure test. So, while we have the area open to replace our decking, we are replacing with the 2" rigid white Sched 40 PVC.

The only place I am forced to use some black flexible PVC is from the bottom of the skimmer 90 degree elbow to meet the run of 2" rigid PVC that connects to the pump intake. The depth of the skimmer and the angle of the end of the trench make it almost impossible to use rigid PVC, so flex is a much better choice there. I may also use some of the black flex PVC to make filter to heat pump connections if needed. But it will all be glued, both below and above ground.

 

[jimmythegreek]

Cant glue black poly only barbs amd clamps. White flex PVC should only be glued and is a step up from poly. Rigid pipe is the Cadillac of them all

 

[coolviper777]

Cant glue black poly only barbs amd clamps. White flex PVC should only be glued and is a step up from poly. Rigid pipe is the Cadillac of them all

I agree, rigid PVC is best if you can run it. The manufacturer says it compatible with both sched 40 slip or barb fittings. It seemed to glue with no issues into the MPT threaded 90 elbow on the bottom of my skimmer, and 3 feet away into the rigid PVC joint. And it held water, but I can't yet run the pump as I still have to run my new main electrical line for the pool. I am thinking that there isn't as much pressure on the skimmer line, and more on the return line, which is all rigid. Is this reasonable thinking?

As luck would have it, Bobcat was digging, and pulled that run of pipe up a bit, and of course permanently bent the flex PVC, and pulled it out of the 2nd joint. It's still well joined at the skimmer. With heavy equipment, something had to give I suppose, better than the rigid PVC or the new skimmer breaking (my model was very hard to find in a 2" outlet)

Amazon.com: FreezeFlex 2 in. x 25 ft. PVC Tubing: Home Improvement

Amazon.com: FreezeFlex 2 in. x 25 ft. PVC Tubing: Home Improvement

www.amazon.com

The manufacturer claims this is Flex PVC....

• Can be frozen solid without losing strength or structural integrity
• Smooth wall interior improves water flow, prevents friction loss
• Flexible, will not collapse or kink around bends or curves
• Works with standard schedule 40 PVC slip or barb fittings

 

[jimmythegreek]

All true above except you do not want to use barbed fittings. That's the weakest joint. Welded solvent glue joints from PVC glue amd primer all the way.

I'm not following the mpt threaded 90. That fitting is male threads on one side and glue on the other. If your implying that you threaded the mpt into the skimmer amd glued the flex into the other end socket than that is the right way.

 

[coolviper777]

All true above except you do not want to use barbed fittings. That's the weakest joint. Welded solvent glue joints from PVC glue amd primer all the way.

I'm not following the mpt threaded 90. That fitting is male threads on one side and glue on the other. If your implying that you threaded the mpt into the skimmer amd glued the flex into the other end socket than that is the right way.

Yes, mpt into the skimmer and glued the flex into the other end socket. It's all done, no leaks. Still hooking up the electrical, but that will be done shortly.

 

[cj133]

I do not install pools, so my opinion may mean very little to some. That said,

I'm not so sure Sch 40 pvc is the Cadillac.
For example polyethene will tolerate freezing where rigid pvc will not. It will also tolerate a lot more physical abuse and is often used underground for potable water lines and even natural gas piping even at higher pressures.

I'd agree a solvent welded joint is better than a barbed fitting but I guess everything has it's pros and cons. From what I understand about them I'd pick poly over flexible PVC by far though.

I was going to do poly for main drains in my above ground pool due to freezing concerns near the edge of the pool but didn't feel like dealing with it so it never happened even though I bought everything.

 

[CJadamec]

So I think something is being lost here at a more basic level.

Flexible pvc was made to meet the demands of certain applications where rigid pipe becomes a Hassel or even a hindrance. A lot of tradesmen refer to flex pipe as "spa pipe" as that is its primary application. It makes wrapping pipe around a spa easy and reduces the need for countless fittings you would need with rigid pipe.

Flexible pipe makes adapting to odd angles and offset equipment easy it saves time and doesn't require pipe fitting skill to line up fittings and joints.

Cleanly fitting and making rigid pipe look good takes time and skill. Both of which are costly.

I can see why some builders would choose to pay the extra money for flexible pipe because it saves so much time on installation.

Personally I think they both have a place and done well they are both equally good options. Id much rather see flexible pipe used like electricians use sealtight conduit. Flexible conduit is basically the same stuff. Long runs are by code required to be in rigid conduit. Code permits the use of flexible conduit in short runs to join the rigid conduit to equipment. Or where conduit needs to flex to allow for machinery movement.

Each material has its place. Both materials are extremely durable when used and installed correctly.

The skill of the plumber is far more important and will have greater impact on the longevity of the installation then wether it's rigid of flexible.

 

[cj133]

So I think something is being lost here at a more basic level.

Flexible pvc was made to meet the demands of certain applications where rigid pipe becomes a Hassel or even a hindrance. A lot of tradesmen refer to flex pipe as "spa pipe" as that is its primary application. It makes wrapping pipe around a spa easy and reduces the need for countless fittings you would need with rigid pipe.

Flexible pipe makes adapting to odd angles and offset equipment easy it saves time and doesn't require pipe fitting skill to line up fittings and joints.

Cleanly fitting and making rigid pipe look good takes time and skill. Both of which are costly.

I can see why some builders would choose to pay the extra money for flexible pipe because it saves so much time on installation.

Personally I think they both have a place and done well they are both equally good options. Id much rather see flexible pipe used like electricians use sealtight conduit. Flexible conduit is basically the same stuff. Long runs are by code required to be in rigid conduit. Code permits the use of flexible conduit in short runs to join the rigid conduit to equipment. Or where conduit needs to flex to allow for machinery movement.

Each material has its place. Both materials are extremely durable when used and installed correctly.

The skill of the plumber is far more important and will have greater impact on the longevity of the installation then wether it's rigid of flexible.

Hi Chuck,
I've heard rumor termites can chew through flexible pvc.
Is this actually a common thing or rare?

I've also always been told PVC and poly shouldn't be exposed to sunlight and yet, it is constantly both on pools and roof vents etc. Seems like it generally holds up very well for a long time.

 

[CJadamec]

All pvc gets brittle when exposed to UV light (sunlight). It also gets brittle to the point of failure often with little to no warning.

A simple light coat of paint is all that is needed to slow down that process and can buy you decades of use out of the pipe. You will notice a lot of pool pads on pools in CA and southwest states have a coat of beige paint on the pipes. Its not just decorative.

Termites can and will chew thru pvc and vinyl. Its something to take into account if you know they are a pest in your area.

I'm not a fan of long buried runs of flexible pipe. I don't thinks it's the right use for the material. Id much rather see the buried runs be rigid pipe. A short piece of flexible pipe to go from hard pipe to pool fittings I would be fine with. It saves time and allows for give and movement at those joints.

If the pipe is buried in gunite I don't think it matters either way what it is.

 

[cj133]

All pvc gets brittle when exposed to UV light (sunlight). It also gets brittle to the point of failure often with little to no warning.

A simple light coat of paint is all that is needed to slow down that process and can buy you decades of use out of the pipe. You will notice a lot of pool pads on pools in CA and southwest states have a coat of beige paint on the pipes. Its not just decorative.

Termites can and will chew thru pvc and vinyl. Its something to take into account if you know they are a pest in your area.

I'm not a fan of long buried runs of flexible pipe. I don't thinks it's the right use for the material. Id much rather see the buried runs be rigid pipe. A short piece of flexible pipe to go from hard pipe to pool fittings I would be fine with. It saves time and allows for give and movement at those joints.

If the pipe is buried in gunite I don't think it matters either way what it is.

I like the idea of short flexible runs.
Every time I see pictures of an Intex pool all plumbed in Sch 40 it makes me cringe. I guess everything has enough give but it just seems bad.

 

[CJadamec]

I like the idea of short flexible runs.
Every time I see pictures of an Intex pool all plumbed in Sch 40 it makes me cringe. I guess everything has enough give but it just seems bad.

Its the actual intended use for the product. To allow for a flexible pipe connection.