PVC drop pipe: male adapters vs threading the pipe

[Paltus]

For 200' schedule 80 1" PVC drop pipe, is it better to glue/weld male adapters or to thread the pipe ?
Have seen arguments both ways so a bit confused why there is no simple answer.

Also for threading pvc pipe, can I just use electric threader I got for metal pipe, or I really have to use
a special PVC threader. What is special about it. Any thread cutting lubricant for PVC ?
I think I am going to thread one end of a short pipe and glue a male adapter to the other end and
then put it under increased stress to see which end breaks first and at what load.

 

[TJanak]

Doesn't answer your question, but I buy threaded sch. 80 pipe and SS couplers from a local driller. Might be an option for you.

 

[Sponsor]

 

[Valveman]

Never glue anything down the well. Like was said you can get threaded sch 80 and metal couplings are best. Water is the only lubricant needed when threading PVC, but you have to go slow and reverse every thread or two to remove shavings and keep the threads clean.

 

[Reach4]

I think I am going to thread one end of a short pipe and glue a male adapter to the other end and
then put it under increased stress to see which end breaks first and at what load.

It still would be an interesting test.

From what I understand, it might take 24 hours for the cemented joint to get to maximum strength, depending on temperature. If putting pipe into a well, waiting for even 15 minutes per joint before applying tension might seem like a long time. So if you test, decide how long you will wait between cementing and applying the test tension.

 

[Valveman]

All plastics have what is called "creep". It may pass the test today, but being put under weight stress for a period of time will cause glue joints to fail.

 

[Jeff H Young]

All plastics have what is called "creep". It may pass the test today, but being put under weight stress for a period of time will cause glue joints to fail.

Having never worked on a well , I've never threaded PVC didn't know this was practice. Helpful Info Cary! Guessing all the weight is on drop pipe? you keep a pull rope on pump while lowering?

 

[Valveman]

Having never worked on a well , Ive never threaded PVC didnt know this was practice. Helpful Info Cary! Guessing all the weight is on drop pipe? you keep a pull rope on pump while lowering?

Nope! All the weight is on the drop pipe, which is why you don't want any glue. But rope is just another opportunity for a failure and should never be put in a well. If your pipe isn't good enough to hold the pump, get better pipe, not rope.

 

[Reach4]

Having never worked on a well , Ive never threaded PVC didnt know this was practice. Helpful Info Cary! Guessing all the weight is on drop pipe? you keep a pull rope on pump while lowering?

Common practice here is white 20-ft schedule 80 that comes pre-threaded, but threading on-site when a shorter piece is needed. No stainless safety cable or rope. Stainless steel couplings or schedule 120 pvc couplings. The PVC needs more skill in not overtightening. When I had my pit demolished, they replaced the plastic couplings with stainless. Reused the same drop pipe. While they suggested a new SQ pump into my 4-inch steel, I had them put my 12-year old Sta-rite Trimline pump back in. If that gets pulled again, I will have them put in the SQ.

My well is about typical here at 140 ft. I neglected to count the number of drop pipe sections. In areas with deeper wells, well people use schedule 120 or 180 pvc typically.

Dope with a brush on the threads, but no tape.

 

[Valveman]

Dope with a brush on the threads, but no tape.

Actually, I run threaded PVC into metal couplings without any dope or teflon, just dry. When it pops a time or two it is tight enough. Dope can soften the pipe and tape makes it slick. Don't want it coming unthreaded from the pump starting, so best to run it dry.

 

[Paltus]

It still would be an interesting test.

From what I understand, it might take 24 hours for the cemented joint to get to maximum strength, depending on temperature. If putting pipe into a well, waiting for even 15 minutes per joint before applying tension might seem like a long time. So if you test, decide how long you will wait between cementing and applying the test tension.

I could weld male adapters ahead of time and let them dry for a week or so. The arguments against threading the pipe I saw are that threaded pipe is rated only at about half the PSI of unthreaded pipe. It actually says so right on the pipe. Maybe it does not extend to any assembly at all but that would be silly if that's the case. If it does extend to assembly then it kind of implies that glue welded assembly is rated at twice the PSI of assembly using threaded pipe. ( what male adapter PSI rating is, is a separate question ).
I'd really like to see some scientific study of comparative strength of welded adapters vs threaded pipe for this application. I understand that improperly welded joints will fail and there are many ways to f.up the welding -- eg not use the primer, or use expired primer, apply it incorrectly, use bad glue, use more of it or less than needed, not allow the joints to cure, etc etc. but if everything is done ~right, which one is better ? that's the question.

In my other well which is only 75', I can see 1" schedule 40 PVC going into it. Since there is no way to thread it, I assume that it is glued one way or another ( what else can it be ? ). Maybe it does not matter for 75' but the well in question is 200' - not that much deeper. For a much deeper well I wouldnt be thinking of PVC anyway...

 

[Paltus]

Actually, I run threaded PVC into metal couplings without any dope or teflon, just dry. When it pops a time or two it is tight enough. Dope can soften the pipe and tape makes it slick. Don't want it coming unthreaded from the pump starting, so best to run it dry.

Do the pumps tend to rotate in the direction that's unscrewing the usual threads or tightening them on start ? Seems like basic engineering and common sense ... though there might be rotational forces in the opposite direction when they stop .. but I'd assume weaker ?

 

[Valveman]

Threading pipe cuts away half the pipe thickness so, it cuts the pipes pressure rating in half. Glued joints have a higher pressure rating, but less weight holding capacity. Sch 40 should not be used in the well as it is not thick enough to thread.

The torque from a pump starting tries to unscrew the pump from the pipe. Rapid cycling has unscrewed the pipe and dropped many a pump in the well. That is why I run them dry. They pop when you get it tight enough, and they have to pop to come unscrewed so they don't.

 

[wwhitney]

The torque from a pump starting tries to unscrew the pump from the pipe.

Nobody makes mirror image pumps that would try to tighten the right-hand threads? Or left hand threaded pipe and couplings?

That is why I run them dry. They pop when you get it tight enough, and they have to pop to come unscrewed so they don't.

Can you expand on what you mean by "pop"? Are referring to a noise from compressing the plastic as it goes into the metal coupling? Or something about how the plastic threads catch in the metal coupling, where you reach a point where you can only tighten it a few degrees at a time, and it makes a popping noise as you overcome the static friction? Or something else?

Cheers, Wayne

 

[Reach4]

I could weld male adapters ahead of time and let them dry for a week or so. The arguments against threading the pipe I saw are that threaded pipe is rated only at about half the PSI of unthreaded pipe. It actually says so right on the pipe. Maybe it does not extend to any assembly at all but that would be silly if that's the case. If it does extend to assembly then it kind of implies that glue welded assembly is rated at twice the PSI of assembly using threaded pipe. ( what male adapter PSI rating is, is a separate question ).

1. These adapters you propose, are they schedule 80?

2. What is the source of the schedule 80 pipe that you propose to use? In particular, if this is gray electrical conduit, I think the composition of those is rather different than regular pressure pipe. I know it has anti-UV additives, and I suspect it has more plasticizers. It feels softer.

In my other well which is only 75', I can see 1" schedule 40 PVC going into it. Since there is no way to thread it, I assume that it is glued one way or another ( what else can it be ? ). Maybe it does not matter for 75' but the well in question is 200' - not that much deeper. For a much deeper well I wouldnt be thinking of PVC anyway...

I think that drop pipes over 600 ft are sometimes used before having to resort to steel. But at some point, it is more than schedule 80.

Regarding schedule 40 pvc with glued (I am going to use that term risking the wrath) connectors/adapters, I would not be surprised that is what you have, and that it works great. A commercial operation won't want to wait a week. Plus, they won't want to do what will be perceived as amateur. Threaded PVC is quick, reliable, and reusable, with 20 ft pipes and a hoist truck.

For DIY dropping hand-over-hand, consider SIDR polyethylene.

And while thinking about it, you might consider converting to a pitless adapter, even if freezing is not a concern. It makes lifting a pump later more convenient. Like the convenience of splicing wires vs having a connector.

 

[Valveman]

Nobody makes mirror image pumps that would try to tighten the right-hand threads? Or left hand threaded pipe and couplings? Cheers, Wayne

Lol! You are gonna make me show my age here. When Grundfos first came to the US, 1973 I think, they had backwards spinning impellers. Makes sense in Europe that the pump should spin in a direction that tightened the drop pipe, and motors can spin either way. Americans took to that about as good as they did the metric system. I really liked the SS pump, took on the brand, and made a lot of accommodations to use those backwards spinning pumps. Franklin made and we stocked special reverse rotation single phase motors. Three phase customers never knew the difference. But Grundfos immediately went to retooling everything for left hand rotation pumps as was the norm in the US.

And yes, this makes it very common for pumps to come unscrewed and fall in the well due to pump cycling. I had a large pump on 4" pipe one time that I even tack welded the couplings after they were tight, and they still torqued lose. Just another one of many things that taught me how bad cycling a pump can be. I digress. Americans are just hard headed. We still measure in feet and inches, our pumps still spin to the left, there are those who still think a diaphragm tank is a new fangled piece of junk, and even more who have not warmed to all the benefits of a Cycle Stop Valve.

 

[Valveman]

Can you expand on what you mean by "pop"? Are referring to a noise from compressing the plastic as it goes into the metal coupling? Or something about how the plastic threads catch in the metal coupling, where you reach a point where you can only tighten it a few degrees at a time, and it makes a popping noise as you overcome the static friction? Or something else?
Cheers, Wayne

Yeah just a "popping" noise. With a pipe wrench in each hand, when I hear it pop a time or two, that is good enough.

 

[Paltus]

1. These adapters you propose, are they schedule 80?

2. What is the source of the schedule 80 pipe that you propose to use? In particular, if this is gray electrical conduit, I think the composition of those is rather different than regular pressure pipe. I know it has anti-UV additives, and I suspect it has more plasticizers. It feels softer.


I think that drop pipes over 600 ft are sometimes used before having to resort to steel. But at some point, it is more than schedule 80.

Regarding schedule 40 pvc with glued (I am going to use that term risking the wrath) connectors/adapters, I would not be surprised that is what you have, and that it works great. A commercial operation won't want to wait a week. Plus, they won't want to do what will be perceived as amateur. Threaded PVC is quick, reliable, and reusable, with 20 ft pipes and a hoist truck.

For DIY dropping hand-over-hand, consider SIDR polyethylene.

And while thinking about it, you might consider converting to a pitless adapter, even if freezing is not a concern. It makes lifting a pump later more convenient. Like the convenience of splicing wires vs having a connector.

To be concrete, eg Lowes.
https://www.lowes.com/pd/Charlotte-...n-dia-Schedule-80-Adapter-PVC-Fitting/3699096
https://www.lowes.com/pd/Charlotte-Pipe-1-in-dia-x-10-ft-L-630-PSI-PVC-Pipe/3356302

Maybe a pitless adapter, right. I need to do something ahead of time such that when the pump ends up falling into the well ( regardless of which way I end up doing it ), it will make me feel better about the whole thing

In the mean time I am also consulting with experienced folks on this forum (thanks guys !) ,
and am going to do a real load experiment on it later this week. Will post results.

 

[Paltus]

Yeah just a "popping" noise. With a pipe wrench in each hand, when I hear it pop a time or two, that is good enough.

factory made threads on PVC or DIY threads ? Or doesnt matter ? made at 40F or 90F ?
Other recommendations for tightening PVC I have seen are eg "two turns beyond hand tight with PVC compatible thread sealant".

Arent there more scientific standards for it ? Torque wrenches are inexpensive. Would love to see a table specifying torques for
PVC + PVC, PVC+SS, etc for different pipe sizes. With or without thread sealants. And then just do what the table says and not
have to worry about my load experiment causing wrong results because I didnt torque things right

 

[Valveman]

factory made threads on PVC or DIY threads ? Or doesnt matter ? made at 40F or 90F ?
Other recommendations for tightening PVC I have seen are eg "two turns beyond hand tight with PVC compatible thread sealant".

Arent there more scientific standards for it ? Torque wrenches are inexpensive. Would love to see a table specifying torques for
PVC + PVC, PVC+SS, etc for different pipe sizes. With or without thread sealants. And then just do what the table says and not
have to worry about my load experiment causing wrong results because I didnt torque things right

Many years ago I bought 1 1/4" sch 80 threaded by the truck load and pallets of galvanized couplings. Today I would probably use stainless couplings. I would hand thread one pipe for every well to make it fit as needed. Threaded them with regular metal pipe thread dies in 100+ degree or below freezing days as needed. Adding dope or paste makes the threads slick and they thread in way more than needed. Even then the slick can make them come unscrewed from the starting torque of the motor. You won't find it in any manual. This is just from having screwed enough pipe together to reach the moon trying many different methods. I found it best to run the threads dry, no tape of paste, and tighten until they make a popping noise a time or two.

 

[VAWellDriller]

FWIW I use SCH80 or SCH120 threaded PVC for all residential jobs.....have used threaded both ends with stainless couplings but mostly use integral bell end pipe cause it's fast and skips a step. We use compatible pipe dope and have found that PVC pipe when put together dry, it is sometimes hard to get back apart. I've never had one unscrew. We regularly thread onsite with a cheap northern tool hand threader and have no problems; no lube.

You asked about torque....it's well published 10 ft/lb per HP of pump. If you've ever watched or held onto a pump starting or stopping, you can feel the torque, and it is practically as much when pump stops, so it wouldn't matter too much if you got a pump to run either direction; it's getting torqued on start and stop.

I've also seen plenty of folks glue on male and female adapters on SCH 40 pipe.....most of the time it's worked but I wouldn't do it. SCH 80 1" integral bell end is about $1.00 / ft and probably rated for double the deadhead pressure of your pump.