Mainline on well system continues to burst.

[Athan]

I've been hired to fix a continuous problem of burst piping on a sports field complex irrigation system. The systems water is provided by a city well. The system is a shared system. Meaning the complex I'm working on and a neighboring sports field use the same well for water. The piping, including the actual joints, continue to burst in half. Not separate but actually break in two. The mainline is 4", then 3", down to 2". The material is schedule 40, some schedule 80 and downstream class 200. Several contractors have walked away from this due to the complexities.
I started with pressure relief valves periodically on the systems mainline in front of irrigation system valves. The hope was to relieve any trapped air in the lines. The lines continued to burst. I'm now onto a pressure regulating valve that I'm installing on the mainline running to the fields I'm responsible for. Now that the mainline for the fields im working on has been shutoff, the mainline upstream is bursting causing issues for the shared neighboring fields. So in short the issue is being shifted upstream. Eventually if the problem gets kicked upstream enough it will come back to the city's well pump. Needless to say the city and the shared sports field personal were happier when the problem was on the lines I'm working on and not pushed upstream to theirs. The city has been very difficult to work with. Any advice would be greatly appreciated
Here's a multi speed curve for the pump that feeds the mainline. The pump service technician for the city has said that:
"the minimum speed is set at 40hz, which would fall at roughly 67% on that chart. Without figuring in drawdown and friction loss, that pump would only run roughly 86psi @ 50gpm. The setpoint on the VFD has always been(and still is) 75psi. I changed a few settings to make it trip out if the pressure gets to 85psi for 1 second. This may cause some nuisance trips, but should also prevent anymore leaks going forward."
When I asked the well depth his reply was: "I'd ballpark static water level at 30', and total depth to be roughly 70'."

I'm not super familiar with pumps and there operation, however I feel there is plenty to learn here. Thank you

 

[Valveman]

Sorry for your problem. This is another perfect example of what happens when using a VFD or variable speed drive to control a well pump. Everything in a VFD has a programmed time things are supposed to happen, like tripping out at 85 PSI after 1 second, or ramping up in a certain amount time. The problem is, transient pressure waves, that cause the water hammer that is blowing the lines, happens much faster. Transient pressure waves travel at 3000 to 5000 feet per second. That is faster than a bullet from a hunting rifle. No valve or VFD can catch or mitigate transient pressure waves or water hammer, you have to prevent it.

There is something like $27B dollars spent on VFD's every year. All the companies who make them want you to think VFD's are the most efficient and accurate way of controlling a pump. They also want you to believe soft starts and slow ramp up times put less wear on the pump, which also is not true. Our government, and many others also promote VFD's and even pay incentives for people to install VFD's. They want you to think they are helping you make your pump more efficient and last longer, when in reality varying the pump speed uses more energy per gallon and causes problems like the transient pressure waves that are blowing up your lines.

I studied electrical engineering and thought VFD's were the best thing since sliced bread until about 1992. But I was having the same kind of problems as you. I have been solving these problems by replacing VFD's with Cycle Stop Valves since 1993. We can even use a Cycle Stop Valve WITH the VFD, so you don't have to replace the VFD until it fails.

It is best to use a CSV with a conventional pressure tank/pressure switch and a standard across the line starter. I installed many of these systems before 2004, and some of them are just now starting to need some repair. Cycle Stop Valves stop water hammer/line breaks and make pumps last many times longer than the designed Planned Obsolescence time frame. Everywhere I install a CSV the customer saves thousands of dollars by not needing an expensive and short lived VFD. I have also been accused of putting people out of business as there have been companies living on the repairs to mainlines. One transmission line in Central Texas had a crew living on location, fixing leaks in the mainline every day. Once the CSV was installed, they were out of a job.

The CSV has a bolt to adjust for the setpoint, similar to a VFD. With the CSV adjusted to deliver the 75 PSI constant you want on the sprinklers, you would need an 86 gallon size pressure tank and a 65/85 pressure switch. The CSV makes the pump start and stop at 5 GPM. This mechanical soft start/soft stop is much better than an electrical soft start. The CSV is also made to operate as fast as necessary. Once the pump starts, any decrease in pressure below 75 PSI causes the CSV to instantly open a bit to keep the pressure at exactly 75. Any increase in pressure above 75 is instantly met with the CSV closing as much as needed to keep the pressure from rising. Even large CSV's work almost instantly. This fast reaction speed is what keeps the pressure at a strong and constant 75 for as long as the sprinklers are running. When no water is being use, the CSV would fill the pressure tank at a rate of 5 GPM, then softly shut down at 85 PSI. The slow reaction of VFD's to these changes in pressure actually accentuate the pressure wave and makes it worse.

To use the CSV along WITH the VFD, you would turn up the set point of the VFD to 85 PSI. With the CSV set at 75 PSI, the VFD would run the pump at full speed all the time and the fast reactions of the CSV would eliminate any water hammer or breaks. When no water is being used, the CSV would slowly fill the pressure tank to 85 PSI, and the VFD would "go to sleep" as they say.

What most people do not understand is that even though the pump is running at full speed the amps or energy used decrease with the flow rate without varying the pump speed. I always like to say a VFD is just trying to trick a pump into doing something it already does naturally. They sell $27B worth of VFD's and people think they are saving energy when they are not.

I guarantee a CSV will solve your problem. However, that is exactly why the pump industry has been fighting Cycle Stop Valves since 1993. The CSV is a disruptive product. It makes pumps last longer and eliminates water line breaks, and that greatly cuts into the profits of people who work in this industry. The CSV can and has eliminated water towers in municipal applications. The companies who build and work on water towers try their best to keep anyone from knowing about a Cycle Stop Valve.

I always thought if you built a better mousetrap, people would beat a path to your door. But I found out if you make a mousetrap so good it could make mice extinct, the mousetrap industry will do everything they can to discredit or keep you a secret. The CSV is also so simple many people accuse me of selling "Snake Oil", Lol. But it really is that simple. Here is a diagram of how simple it is.

 

[Sponsor]

 

[Valveman]

Here is the horsepower drop at full speed. You can see the horsepower drops from 16HP at 200 GPM to only 9HP at 5 GPM. Pumps do this naturally. They do not need a VFD to reduce the power consumed.

 

[Reach4]

The piping, including the actual joints, continue to burst in half. Not separate but actually break in two. The mainline is 4", then 3", down to 2". The material is schedule 40, some schedule 80 and downstream class 200. Several contractors have walked away from this due to the complexities.

I presume you mean PVC rather than steel. Steel pipe up to the regulator would prevent breaking.

I expect the schedule 80 was less likely to burst. In some well work, they will use schedule 120 pipe with schedule 160 pvc fittings. Since the ID of the pipe is the same for PVC of a nominial size, you can use different schedule fittings than the pipe.

I presume you have checked that the breaking pipe is not DWV-only foamcore pipe. Schedule 40 is a size, and most schedule 40 3- and 4-inch, and probably 2-inch PVC sold is DWV-only rather than being dual or triple-rated for pressure. There are ASTM standard markings that can be used to distinguish.

 

[Athan]

Thank you for the questions. Yes, PVC pipe. I apologize for not specifying. And yes, certainly not DWV pipe being used.

 

[Athan]

Sorry for your problem. This is another perfect example of what happens when using a VFD or variable speed drive to control a well pump. Everything in a VFD has a programmed time things are supposed to happen, like tripping out at 85 PSI after 1 second, or ramping up in a certain amount time. The problem is, transient pressure waves, that cause the water hammer that is blowing the lines, happens much faster. Transient pressure waves travel at 3000 to 5000 feet per second. That is faster than a bullet from a hunting rifle. No valve or VFD can catch or mitigate transient pressure waves or water hammer, you have to prevent it.

There is something like $27B dollars spent on VFD's every year. All the companies who make them want you to think VFD's are the most efficient and accurate way of controlling a pump. They also want you to believe soft starts and slow ramp up times put less wear on the pump, which also is not true. Our government, and many others also promote VFD's and even pay incentives for people to install VFD's. They want you to think they are helping you make your pump more efficient and last longer, when in reality varying the pump speed uses more energy per gallon and causes problems like the transient pressure waves that are blowing up your lines.

I studied electrical engineering and thought VFD's were the best thing since sliced bread until about 1992. But I was having the same kind of problems as you. I have been solving these problems by replacing VFD's with Cycle Stop Valves since 1993. We can even use a Cycle Stop Valve WITH the VFD, so you don't have to replace the VFD until it fails.

It is best to use a CSV with a conventional pressure tank/pressure switch and a standard across the line starter. I installed many of these systems before 2004, and some of them are just now starting to need some repair. Cycle Stop Valves stop water hammer/line breaks and make pumps last many times longer than the designed Planned Obsolescence time frame. Everywhere I install a CSV the customer saves thousands of dollars by not needing an expensive and short lived VFD. I have also been accused of putting people out of business as there have been companies living on the repairs to mainlines. One transmission line in Central Texas had a crew living on location, fixing leaks in the mainline every day. Once the CSV was installed, they were out of a job.

The CSV has a bolt to adjust for the setpoint, similar to a VFD. With the CSV adjusted to deliver the 75 PSI constant you want on the sprinklers, you would need an 86 gallon size pressure tank and a 65/85 pressure switch. The CSV makes the pump start and stop at 5 GPM. This mechanical soft start/soft stop is much better than an electrical soft start. The CSV is also make to operate as fast as necessary. Once the pump starts, any decrease in pressure below 75 PSI causes the CSV to instantly open a bit to keep the pressure at exactly 75. Any increase in pressure above 75 is instantly met with the CSV closing as much as needed to keep the pressure from rising. Even large CSV's work almost instantly. This fast reaction speed is what keeps the pressure at a strong and constant 75 for as long as the sprinklers are running. When no water is being use, the CSV would fill the pressure tank at a rate of 5 GPM, then softly shut down at 85 PSI. The slow reaction of VFD's to these changes in pressure actually accentuate the pressure wave and makes it worse.

To use the CSV along WITH the VFD, you would turn up the set point of the VFD to 85 PSI. With the CSV set at 75 PSI, the VFD would run the pump at full speed all the time and the fast reactions of the CSV would eliminate any water hammer or breaks. When no water is being used, the CSV would slowly fill the pressure tank to 85 PSI, and the VFD would "go to sleep" as they say.

What most people do not understand is that even though the pump is running at full speed the amps or energy used decrease with the flow rate without varying the pump speed. I always like to say a VFD is just trying to trick a pump into doing something it already does naturally. They sell $27B worth of VFD's and people think they are saving energy when they are not.

I guarantee a CSV will solve your problem. However, that is exactly why the pump industry has been fighting Cycle Stop Valves since 1993. The CSV is a disruptive product. It makes pumps last longer and eliminates water line breaks, and that greatly cuts into the profits of people who work in this industry. The CSV can and has eliminated water towers in municipal applications. The companies who build and work on water towers try their best to keep anyone from knowing about a Cycle Stop Valve.

I always thought if you built a better mousetrap, people would beat a path to your door. But I found out if you make a mousetrap so good it could make mice extinct, the mousetrap industry will do everything they can to discredit or keep you a secret. The CSV is also so simple many people accuse me of selling "Snake Oil", Lol. But it really is that simple. Here is a diagram of how simple it really is.
View attachment 106181

Absolutely amazing explanation! Thank you very much for taking the time to respond and communicate this to me.
I'm not super versed in pumps, however seasoned veterans like yourself willing to take the time to help us less informed individuals understand, is absolutely invaluable.
Very grateful.

 

[Athan]

Here is the horsepower drop at full speed. You can see the horsepower drops from 16HP at 200 GPM to only 9HP at 5 GPM. Pumps do this naturally. They do not need a VFD to reduce the power consumed.

View attachment 106183

Thank you

 

[Fitter30]

Have you adjusted ramp speed on the vfd to slow it down on the ramp up to 60 seconds. When pressure trips off at 85lbs what is the differential setting? Would want it to drop below minimum vfd pressure either by pressure switch or might be a setting for time off delay in vfd.

 

[Athan]

Have you adjusted ramp speed on the vfd to slow it down on the ramp up to 60 seconds. When pressure trips off at 85lbs what is the differential setting? Would want it to drop below minimum vfd pressure either by pressure switch or might be a setting for time off delay in vfd.

Thank you for your question and taking interest. This has been by far one of the most difficult investigations I've had to deal with.
I will reach out the pump technician and inquire on the differential setting. At this point the city hasn't been easy to work with at all and they have gone out of their way to provide any kind of information.
The tech they're hiring for pump work is someone I've worked with before on other projects. I'm confident I can get info from him. Let me see what I can find. I'll report back. Thank you again.

 

[Valveman]

It doesn't matter what the ramp up time or differential is. Any programed time will not meet the changes in the demand quickly enough. A decrease in system pressure must be instantly met with an increase in flow. An increase in pressure must be instantly met with a decrease in flow. When there is a big demand and the pump is taking 60 seconds to ramp up, the system pressure drops dramatically. Then when the pump finally ramps up enough to meet the demand, there will be a spike in pressure before the VFD has time to slow the pump down again.

The Cycle Stop Valve is a very fast acting valve. An 8" CSV can close down from 2000 GPM to 5 GPM in less than 2.5 seconds. It can open even faster. The pressure downstream of a CSV is instantly met with flow when needed, and flow is instantly reduced when pressure increases. This keeps the system pressure rock solid at the set point, regardless of how many or how fast valves in the filed are opened or closed.

You are dealing with people who don't want to fix the issue. If all the problems went away, they would be out of a job, just like politicians.

 

[Athan]

Have you adjusted ramp speed on the vfd to slow it down on the ramp up to 60 seconds. When pressure trips off at 85lbs what is the differential setting? Would want it to drop below minimum vfd pressure either by pressure switch or might be a setting for time off delay in vfd.

When I asked the pump technician, his reply was this.

"I believe the set point is 75psi. Overpressure should trip when it's at 85psi for 1 second. I do not know if that is a manual or automatic reset, but if it's automatic, then it should kick on again at 65psi."

I'm beginning to think he isn't as familiar with the system as it sounded like originally.

 

[Reach4]

I am thinking that a well pressure tank with the precharge set to maybe 80 or 90 psi, just before your regulator, could serve as a shock/hammer arrestor. I don't know what to suggest for size.

I am not sure of the ideal precharge. My first thoughts were maybe 150 (a few tanks allow that much). On the other hand, maybe 70 would be better. My comments are not based on experience. I am thinking that a higher air pressure makes the tank normally not hold water, that would be better if freezing happened. On the other hand, if there was some water that froze, it would still be ok because expansion would not be constrained.

https://www.menards.com/main/search.html?search=pressure+tank&sf_categoryHierarchy=Plumbing_8342%7EPumps+%26+Tanks_8671&sortBy=priceAsc&brandName_facet=Global+Water+Solutions&brandName_facet=State

https://www.supplyhouse.com/sh/control/search/~SEARCH_STRING=well%20x%20trol

Tanks under 32 gallons and above 10 gallons normally have a 1 inch FIP connection.

 

[Valveman]

A bladder/diaphragm style tank is teed off the main line with like 1 1/4" pipe. A transient pressure wave "shooting" down a 4" main line at 5000 FPS is not going to make a right turn to go into any tank(s). It just blows off the first elbow it comes to.

A big hydro tank where water goes in one end and comes out the other can catch a transient wave. A 2000 gallon hydro tank would hold a couple hundred gallons as the rest would need to be air space. But placed before a pressure reducing valve may not be a good idea, as the pressure could increase rapidly and get very high.

When a hydro tank is used as control for the pump a pressure switch would shut the pump off immediately if the pressure got to a certain set point.

 

[Reach4]

A bladder/diaphragm style tank is teed off the main line with like 1 1/4" pipe. A transient pressure wave "shooting" down a 4" main line at 5000 FPS is not going to make a right turn to go into any tank(s). It just blows off the first elbow it comes to.

So that would take a tee with the tank off of the straight-line path, and the path to the regulator off of the side (the "bull").

To get 1.25 inch all of the way to the tank usually means using a tank of greater than 32 gallons, because for 10 to 32 gallons , the usual is 1 inch.

But still, even if not fully that, it still has to be significantly easier on the pipes than without.

 

[Athan]

Thank you everyone for your comments and questions. To date the problem remains.
The city has been uninterested in doing anything to their system, claiming their system is not the problem. The client I work for is pursing their own well and pump system to be independent of the city and the city's constant denial.

One of the fields in this complex I'm working in is ran on its own independent well system. They became tired of the city's inability to work well with others and hired us to renovate their system last year.

Hopefully we can get my current clients water service restored once their well is complete and things back up and running soon for them.
Thank you again everyone for your thoughts on this. At the very least this has been a wonderful learning experience for me.

 

[Valveman]

With the new well pump, tell then not to fall for the "soft starts of the VFD eliminating water hammer". They have been there and done that. Will have the same problem if they use the same type of pump control.

 

[Athan]

With the new well pump, tell then not to fall for the "soft starts of the VFD eliminating water hammer". They have been there and done that. Will have the same problem if they use the same type of pump control.

Thank you Cary. I'll keep your contact info close. If I run into further issues, I'll reach out. Truly appreciate your explanation. It has cleared things up in mind pretty well.