Deep well - PVC crack between pump and torque arrestor

[Steve L]

This is a very deep well - 1200'. The bottom 600' are schedule 120 PVC, the top 600' are galvanized steel.

All was well for the first 5 years. I accidentally let it run dry for too long. The pump seems fine, but the PVC split open between the top of the pump and bottom of the torque arrestor, about 3 feet above the pump. That's certainly a weak spot, with constant torque when the pump is running. I really don't want to use galvanized steel below the water line. What other options ?

Thanks

 

[Reach4]

What is your check valve situation? With a check valve above the water surface, there could be some water hammer. If you got a check valve able to stand the full pressure, that might make things easier on the pipe.

If you went to a length of stainless pipe above the pump, would that just move the failure point up a bit?

I am not a pro.

 

[Sponsor]

 

[Valveman]

I didn't think you could go that deep with PVC. But 1" shows to be good to 720 PSI and 1 1/4" is good to 600 PSI. That means even with a 40/60 switch 1 1/4" should be good to 1,248', and 1" even more than that. But like Reach says having multiple check valves in that line can cause water hammer that could be 5-10 times that much pressure. Running the pump dry and getting the pipe hot could have also caused that problem. You need a Dry Well protector like a Cycle Sensor, and a couple of good check valves right on the pump and none further up the line.

 

[Midriller]

What is your check valve situation? With a check valve above the water surface, there could be some water hammer. If you got a check valve able to stand the full pressure, that might make things easier on the pipe.

If you went to a length of stainless pipe above the pump, would that just move the failure point up a bit?

I am not a pro.

Any quality pump manufacture REQUIRES a check valve every 100' pumps set over 150', multiple check valves do not cause water hammer poor quality check valves do.(i.e. Stock poppet check valves) This is done to eliminate the amount the amount of head pressure on each check valve on start up. Think of it like a train starting off. I would love to hear how a spring loaded check "causes water hammer" above static water level.

 

[Valveman]

Anymore than one check valve in a submersible pump line will cause water hammer on pump start. It is not a matter of if, only when. As long as the bottom check seals as well and works as fast as the upper check(s) there is no water hammer. But when the bottom check starts closing more slowly or leaks back even a thimble full of water, hammer will happen on pump start. Then the upper check(s) are holding water in the drop pipe the same way putting your finger over a straw full of ice tea holds water in the straw. Water below the upper checks is being held at a negative pressure. Now when the pump comes on it sees a negative pressure instead of positive pressure. This lets a 10 GPM pump try to start at 15-16 GPM. It only has to pump a thimble full of water to re-pressurize the water below the upper checks. So the water below the upper checks flies up and hits the upper checks like a boxer hitting you in the nose as hard as he can. There will be a loud water hammer thump when the pump starts. And if any faucet is open during this time it will spit a pulse of water from the pressure surge.

This kind of pressure surge is what splits pipe, especially at the bottom of the well. When you hear or feel that water hammer thump, the pressure just spiked 5-10 times more than the pump can even build. Water crashes into each additional check valve on the way up, similar to a freight train hitting boulders on the track as it goes further down the line.

I know the books say to use a check valve every 200', but the books are wrong. The pump companies want extra check valves just to make sure the pump does not spin backwards. Multiple check valves maybe a good safety for that, but causes water hammer and split pipes. I have spent a half century removing or telling people to remove the extra check valves to solve the water hammer problem, which it does. By eliminating cycling and having a mechanical soft stop from a CSV the one check valve at the pump will not wear out, which is the real reason most people use more than one check valve.

 

[Midriller]

I strongly disagree, a sticking check valve can cause water hammer as it slams shut. Multiple check valves will not, each check valve represents the bottom of your water column pressure for that section. Your theory is correct if there is only a check valve at the top. The reason you space them out is to lessen the "blow" of the boxer hitting you in the face. Now imagine what a 700' water column at 60 psi would do if your single check valve above the pump stuck open for just one second then slammed shut. It would blow the pump off the bottom. I have never once seen 1" or 1-1/4" galv. split open. Quality check valves are key. I will never say the guys who wrote the aim manual, who have degrees in fluid Dynamics and field experience helping out drillers who don't understand are wrong.

 

[Valveman]

I have to correct those guys with degrees in fluid dynamics all the time. Just because it looks good on paper doesn't mean it will work in the real world. Those are the same guys who think VFD's save energy. LOL!

Go to some classes by Cla-Val and you will get a completely different idea of water hammer. I have given many classes on water hammer to engineers and engineering firms over the years. I can assure you having a degree doesn't mean they know what they are doing.

Negative pressure and transient pressure waves set up between multiple check valves and cause hammer, where that doesn't happen with only one check valve at the bottom. Multiple check valves may help on pump shut down if the bottom check sticks in the open position. But then the negative pressure between the bottom check and the first good one is what causes water hammer on pump start. I have seen this cause 500' of 4" steel pipe to jump a couple feet straight up off the well slab. I have argued with pump guys about this for years. I have even offered to pay for the pull and set if removing the additional check valves didn't solve the water hammer problem. Never had to pay for a pull and set yet.

Oh and BTW, a single check valve won't stick in the open position if you don't cycle the pump too much and have a mechanical soft start and soft stop.

 

[Midriller]

Again you are assuming there is no bottom check valve or the bottom check valve has failed this is THE ONLY WAY to get negative pressure. If you put two check valves below static you (I.e. stock check then a midwest spring check directly above it. Hydraulic pressure can not be a negative in standing column, therefore if either check fails the other backs it up. If both do fail your effects of water hammer are only multiplied by the column of water from static to the next check. Which is ideally 40' or less above static. This setup will never cause water hammer as you have 3 checks that cannot cause hammer. The rest are to isolate water columns to eliminate premature check failure due to 360 PSI or so of static water pressure in a 700' string. This is best practice in my experience. The idea that soft start and soft shut down will save a check is also not one i agree with. VFD/CSV's have ruined more check valves than short cycling due to check valve "chatter" that happens at low production thes systems open and close that valve dozens of times per cycle. Any well driller who has dealt with a low producing stab well/jet pump can verify this as at 2 gpm of less an 1-1/4 check valve will rattle and cause failure. They make VFD/CSV check valves for this now. The only "check valves" i see stick open are the crappy stock poppet valves that come stock on most pumps. the seal is comprimised/debris is caught in them. or they stick closed (suction side of jet pumps) This water hammer is a non issue in my world, so to say multiple check valves causes water hammer is false. Improper installation of check valves causes water hammer, my way works for me, if your way works in your world more power to you........

 

[Reach4]

Again you are assuming there is no bottom check valve or the bottom check valve has failed this is THE ONLY WAY to get negative pressure. If you put two check valves below static you (I.e. stock check then a midwest spring check directly above it. Hydraulic pressure can not be a negative in standing column, therefore if either check fails the other backs it up.

If the bottom check valve had a tiny leak, but there is no check valve far from the pump, the pressure tank will make up the difference, and possibly let a slow check valve at the bottom close the rest of the way.

 

[Midriller]

If the bottom check valve had a tiny leak, but there is no check valve far from the pump, the pressure tank will make up the difference, and possibly let a slow check valve at the bottom close the rest of the way.

True, but your check valves will fail more rapidly from holding higher static pressures, on shallower wells 1 check is all that is needed because we have very little static pressures in comparison to a system that requires multiple checks and installing checks where you should not can lead to issues. But to make the blanket statement that multiple check valves causes water hammer is ignorance..... failed check valves can cause water hammer if someone improperly installed another where it shouldn't be.

 

[Reach4]

failed check valves can cause water hammer if someone improperly installed another where it shouldn't be.

Do you try to avoid check valves above the water line?

 

[Midriller]

Do you try to avoid check valves above the water line?

If the pump is set shallow (under 200') I use 1 check valve at the pump, over 200 I use multiple check valves. Its not about "trying" anything. There are rules, if you follow them you don't have issues, if you install check valves willy nilly wherever you please, you can have issues.

 

[Valveman]

Rules are like science, it is not settled. There is a rule that I should change the oil in my car every 3000 miles. But that rule is made by people who sell oil, as most cars can go 10,000 miles or more without needing the oil changed. Check valves are the same way. People who sell check valves made those rules. Pump manufacturers go along with it, because multiple check valve should insure the pump doesn't spin backwards, which is all they care about.

As long as all the check valves work perfectly there is no water hammer. But as soon as one of them starts closing slower than the others or leaks back a few drops, which is a matter of when not if, water hammer on pump start is imminent.

If the "rules" works a hundred percent of the time I wouldn't be asked to help solve water hammer problems each and every day. Before this day is over I will have at least one person tell me they followed all the rules and they still have hammer. They will think I am crazy for recommending the removal of any additional check valve except for the one on the pump. But they have already been told to add additional check valves and that didn't solve the problem. Removing the additional check valves ALWAYS solves the problem.

Not every system with multiple check valves will have, or at least will not notice the water hammer. Out of about 30,000 systems I work on every year only maybe a hundred will notice this problem. So someone who does a hundred or even a thousand pumps a year may never see it, but that doesn't meant it isn't happening. Other Engineers call me after they have followed all the "rules" and still can't get rid of the hammer, so I see a lot more of these problems than most. Even though only a hundred out of thirty thousand notice the hammer, there are many others who just don't know it is happening.

 

[Midriller]

You pull 82 pumps a day and still have time to be on here.....
You mean like the CSV guy saying CSV's cure all your well problems............
I can drain the oil out of my car and it solve my oil leaks but am I better off?????
My experience in the industry, pulling pumps every day, and my mentors give me my information. The scholars just back it up.
Also if you "solve" the water hammer issue (that is caused by a leaking bottom check) by removing the "good" check valves which's forces the bottom check closed for awhile, until it fails completely (cause it was bad in the first place) Which will cause your pump to nonstop cycle until it gets noticed or fails. OOOORRRR you could pull the pump and replace the check valve that was bad in the first place and get two birds, one stone. Im not the band aid for a bullet wound kinda guy, but to each his own

 

[Valveman]

You are right, I don't have time to argue with you. I will have 82 more pump system problems to solve for people today. You can do a search on this forum and see how many times removing the above ground or second check valve solved the water hammer on pump start problem. I got over 200 to read when I did the search. Most of them read like this.

Removed the check valve near pressure tank and the pressure held steady, so there is no leak in the line to the pump. The water hammer is gone. Success!
https://terrylove.com/forums/index....and-water-hammer-at-cut-in.81238/#post-587263

I would much rather discuss transient pressure waves and hydro or thermal dynamics than get into chest thumping over who has the most experience, but OK.

I haven't pulled a pump for anyone else since 1998 when I sold my pump company. Prior to that I spent 30 years running up to a half dozen pulling units and 2-3 drill rigs at the same time, building and installing more than 2000 pumps a year. With that many rigs running I never got to see the normal 1HP pull and sets. All I got were the problems. Water hammer, repeated failures, fishing jobs, pumping salt water or hot water, pumping out of lakes or 2000' deep wells, lost circulation, or any other problem job was the one I got. While everyone else was doing the 1900 regular jobs, I got the 10o jobs a year that nobody else could figure out, which taught me a lot.

I had many mentors over the years, one of which actually wrote most of the AIM manual. However, all of them are dead and gone and I realized now I am the old man with more than 50 years experience. I went to my first pump school at Reda in 1973, and I had already been working on pumps for years. I have been the one teaching those classes for the last 25 years or so.

Now those 82 CSV's I sell everyday are to solve 82 pump system problems. No one ever calls me or gets a CSV unless they are already having problems. When pump guys suggested more check valves, extra pressure tanks, VFD's, or any of the other things that didn't solve their problem, they finally call me. The CSV really does cure most pump problems. It is the only product I know of that has been blacklisted by Goulds and several other pump companies for working too well. When I heard CSV's had been black listed for "making pumps last longer and using smaller tanks", I knew there was more to it than I could see. So I have spent the last 26 years figuring out all the reasons the CSV can solve so many pump system problems. I think that gives me more experience than just about anyone in the business.

And you are also right that if the bottom check is bad and needs replacing, the top checks were just masking the problem. Replacing or adding additional check valves will not solve the problem. I see it as adding a cast on your arm for a small scratch, not gonna help. Just make sure the bottom check is good and the pump doesn't cycle too much and you don't need anymore check valves to cause further problems down the road.

Now if you want to talk transient pressure waves and how to prevent them I am all for it. But if you want to just continue to insult me, we are done.

 

[Midriller]

I understand what your saying but how do you get transient waves when your second check valve is below or less than 40' above static. you don't.... and as long as water cannot leave the string from a column of water that extends past 40' above static no water hammer is possible.... no exceptions These are laws of fluid dynamics not opinions.

 

[Valveman]

Any check valve above the static level will cause a negative pressure if the bottom check closes too slowly or leaks back a few drops. Extra check valves below the static cannot cause a negative pressure, but if the bottom check leaks there will only be static head below the second check. The second check valve up the string is still holding everything above the static level, plus the 40 PSI from the system with a 40/60 switch. It doesn't matter if it is a negative pressure or just static head, there is still less pressure below the second check than above it. This lets the pump come on against negative pressure or only the static head. At start up the pump is producing maximum flow, because there is nothing holding it back. However, it may only take a thimble full of water to re-pressurize the tiny amount that leaked from the bottom check. The pump comes on and produces that thimble full of water in about 1/1000th of a second. Then you have max flow from the pump hitting a fully closed, or multiple fully closed check valve(s) with everything above the static level plus 40 PSI holding it/them closed.

Water hitting that upper fully closed check valve will cause a transient that reflects back to the pump, and can actually shatter the thrust bearing, especially after this process is repeated over and over from cycling. While the pressure wave is being reflected back to the pump, the 200-300 PSI below the second check valve, which may only have 100 PSI above it, also instantly pops open the second check valve. The resulting shock wave from the pump starting punches this second check valve like a prize fighter punching you in the nose as hard as he can. This sends a second transient wave up the line, which hits the next check valve, and so on, until all checks in the line are open. The shock wave from these checks popping open causes such a surge of pressure up top, that the pressure switch can bounce on/off rapidly before the pressure tank has time to absorb any water. The water hammer pulse is so fast that it maxes out the pressure switch before the bladder in the tank can absorb the pulse.

When the only check valve is right on the pump this cannot happen. That check valve is holding all the water above static plus the 40 PSI from the 40/60 switch. So when the pump comes on it instantly sees the pressure needed to make up for the lift and pressure required, and isn't allowed to throw itself to a wide open flow rate. The pressure it takes to push that bottom check open will make the pump start at a reduced flow rate, and it won't send a shock wave up the line or reflect one back down at the pump. The pump will start at whatever flow rate it can produce against the lift and pressure above it.

It is even better when there is a CSV up top in the 1 GPM or 5 GPM position on pump start. Now the pump starts with enough pressure against it to make it only produce 1 GPM or 5 GPM, instead of the whatever flow it can produce against the head and pressure above it.

 

[Valveman]

VFD/CSV's have ruined more check valves than short cycling due to check valve "chatter" that happens at low production these systems open and close that valve dozens of times per cycle. Any well driller who has dealt with a low producing stab well/jet pump can verify this as at 2 gpm of less an 1-1/4 check valve will rattle and cause failure. They make VFD/CSV check valves for this now.

Also wanted to discuss this with you. Check valve chatter is much worse with a VFD than without. It is hard to see the water coming right out of the pump, and even harder to see what is happening in clear water. I found this clip of a manure pump that shows water coming right out of the pump, and the manure adds some "color" so you can see what is happening.

The blades in a centrifugal impeller sends the water out in slugs. When the pump is running at full speed these "slugs" of water are so close together you can barely see them. Find a clip of a manure pump working at full speed and you can see the separations in the water, but the slugs are so close together they just look like turbulence.

This clip shows a manure pump at slow speed and you can see the separate slugs of water in the flow. The slower the pump speed, the more distance there is between the slugs of of water. This is why check valves chatter so much at low flow when using a VFD.

However, when using a CSV the pump is still spinning at full speed and the slugs of water almost make a continuous flow. The mostly closed CSV at the top of the well is actually compressing these slugs of water together, and they don't show up as separate waves and make the check valve chatter. We have never needed a special check valve for Cycle Stop Valve systems. Those special "VFD check valves" are just one more Band Aid for yet another problem caused by varying the pump speed with a VFD.

 

[Midriller]

Your equating a single stage manure pump to a 9 stage or better well pump. Stages are offset for this reason....... The reason a check valve chatters is because the low flow CSV or VFD just tips one side of the check valve open and the check valve rocks back and forth. Flomatic, (who makes the best CSV's) showed us a video of this at my last Groundwater Seminar. You should talk to those "check valve crooks" they may teach you something, I mean who knows their product better than they do.

 

[Valveman]

Lol! They do make a good copy. They should, they have been stealing my ideas for 26 years. I agree with you some on the tilting check valve. But it does the same with a silent or double door check which can't tilt. So the pulsing does have an effect on the chatter. And your right about multiple stages to a point, but the top impeller has the most effect. Plus they use those on a lot of single stage pumps as well.