Backflow preventors 4

[okieduck]

Hi everyone!
Our city is researching the issue of backflow preventors and double detector checks. The problem is, we have researched EPA, AWWA, and other agencies for standard specifications and can not find any. Basically it is up to the local authorities to determine what shall be used. If anyone has experience in this area, I would appreciate some guidance. Currently we use 4"-10" DDC and we are looking to reduce the cost of installation.
Thanks for your time!
Joy

 

[KRSServices]

I wish you the best of luck on that one. May I ask what precipitated the issue of backflow preventers in your city?

They are incredibly costly to not only install but to maintain as well. I have had some experience with the politics and frustration with implementation of a program, but for the most part, it was a warm and fuzzy undertaking for the newbies but did nothing to globally address the issue for existing services.



KRS Services

http://www.krs-services.com

 

[BobPE]

The EPA is currently working on guidance on back flow prevention programs and may actually take primacy on them with regard to public water systems in the near future. I have done several programs with the most interesting being for the government itself. Your on the right track in planning because it is an expensive undertaking. I would recommend getting a good engineering firm to assist you due to the nature of the liability of the program.


BobPE

 

[okieduck]

KRSServices,
Thanks for your reply. Of course, the reason we are investigating this is because of money. A 4" DDC can be placed in a can, but 6" and larger has to be in a vault. The vault is a big majority of the expense, so if the detector is not in a traffic zone, I was considereing having a company quote prices for bigger cans. Just brainstorming. It has been a very interesting project so far, and I have learned alot.

 

[saxon]

okieduck, Here in Chicago, backflow preventers have been a requirement for the last seven years on new installations. Older installations have been grandfathered, until they are revised or modified then back flow preventers must be installed. As for the responsiblity of buying and installing, that belongs to either the archtectural firm doing the building (passed along naturally to the buyer) or by the owner of the property. As for installation, they are installed inside the buildings at the service connection after the meter. Remember, these things must be tested regularly to ensure that they are operating correctly. Simply installing these things and walking away is not enough.

As for the type of backflow preventer used, it is a Reduced Pressure Zone Preventer comprised of double checks, double blocks and pressure relieviing valves. You're quite right in the fact that these things can get huge in larger sizes. If the meter is in a vault that's got to be increased in size as well in order to accomodate. As for the costs, just ask yourself "What price the Public's heath and safety?" I know plenty of Tort Lawyers who would love to get their hands on liability cases involving contaminated water.

saxon

 

[bimr]

okieduck,

I believe the information that you are looking for will be found in the plumbing codes.

 

[fel3]

okieduck…

I just happened upon this thread, so perhaps I am a bit late. Also, this is not my area of experise, and our water quality guru has gone home for the evening. Hoever, I seem to recall that here in California much of the background work on this issue from a water quality standpoint was done at the University of Southern California and I believe the organization on campus is called the "Center for Cross-Connection Control" or something like that. An internet search should turn up some info you can use.

Fred

 

[cr2]

okieduck...

I also just happened upon this thread. Not sure what state your in, but in CA the Dept. of Health Services Div. of Drinking Water issued requirements for backflow prevention assemblies in 2002. Those requirements may be of some help.

cr2

 

[okieduck]

Thanks for all your replies. Im in Oklahoma, and frankly what Ive found for standards here is in question. USC and AWWA have helped in my research. Developers for our town have complained about the cost of these programs, stating they are a too expensive for progress. That is not true compared to the millions of dollars they spend just to develop. I love the political game!
Thanks again for your advice.

 

[saxon]

okieduck, As for the political game, just tell the developers, or have your attorneys tell them, since they are building and attaching to a public infrastructure service, they are taking on and accepting the liability of potential backflow and contamination of the public water supply. Then have their lawyers explain the liabilities, to the developers that they are taking on. You'll be amazed out how fast they fall in line. They will see the cost of purchase and installation now becomes cheap Tort Insurance.

saxon

 

[KRSServices]

Okieduck,

You clarified a point that has been bothering me about your original thread. Up here where it is somewhat cooler, many backflow preventers are installed within the building or compound themselves, versus a vault or similar structure. Along with that, usually the meter is within proximity and therefore access is not usually an issue.

I must reiterate my initial response however. Is backflow prevention a criteria developed by the municipality to protect the water distribution system from contamination, or is it a warm and fuzzy get to feel good project for new developments and services? I ask because unless backflow prevention is systatically implemented and integrated in the distribution system it is not very effective and proven to be a wee bit of a burden on already strained budgets. Case in point, two commercial buildings (allowing a variety of uses), one constructed 20 years ago, the other approved for construction by the municipality. The newer building has backflow prevention by statute, the other is grandfathered. How is the system protected if the system goes into draw (vacuum)?

I have personally experienced and entire system go into vacuum (reverse pressure) affecting a town of 2,800 people. I too was a big believer in backflow prevention until this incident. We were very lucky that contamination of the system was not reported and the entire system was immediately flushed. Case in point, the only way to prevent widespread contamination was to isolate the distribution system. Had backflow preventers been installed on each and every service, and proven to be in good working order, the risk of contaminatin would have been dramatically reduced however, the resulting actions by my staff would have been the same. So in the end, could your City respond to an event like we did, and given your present backflow prevention program, would it really make a difference?

In additon to the other considerations raised by the other threads, you must also look at public safety and how it is best being served diligently.

Incidently, I recieved unanimous funding to install numerous additional "emergency" isolation valves throughout the system and complex monitoring devices as a response to that event ever occuring again.





KRS Services

http://www.krs-services.com

 

[okieduck]

KRS-Services,
Could you possibly elaborate a tad more on how your company isolated the system?
I have decided to recommend a detector check or at least a check valve in the street with the double detector in the building. We can even use meter cans for 4" and 6". We are concerned 1st with public safety. Our city has offered to pay some of the cost. Now that we have dug that hole with a tight budget, an acceptable but less costly method needed to be implemented.
Thanks for your time!
Joy

 

[hydrae]

Okieduck

Remember everywhere you install a check valve, somebody will need to repair that check valve 10 to 20 years from now. I have run accoss check valves that lost the hinge mechanism then the disk flopped around blocking flow at very random times. The check valve was buried at the curb.

The best backflow prevention device is education of your customers to not install hazards or if they install the hazard to also install the protection.

Hydrae

 

[KRSServices]

Okieduck,

My company did not isolate the system, I was the Director of Utilities for a municipality. I got the phone call at 6:30 pm from a concerned citizen complaining that he had no water and further, his kitchen sink was making a "sucking" sound (like a vacuum cleaner). That scariest moment of my life because it was the last day on a long, hot and dry long weekend and there was physically no mechanism to warn the community completely.

What we did (as a post mortem) was to re-affirm our pressure zones and critical consumption areas (hotels, hospital, restaurants, etc.) and apply first response to isolate these zones. Many had existing valves, but some were required to be repaired and new ones installed. Emergency Plans were drawn up and improved detection systems were installed. Many larger communities already have these sytems on their reservoirs so it is not an issue. In addition, an employee was required to check the reservoir levels every day, including holidays.

One question that you may want to ask yourself is in the event that your system goes into siphon, how quickly could you react and what would be the ramifications with your system (including existing backflow preventors, workable or not)? What would be the probability of a siphon situation or a short term negative pressure drop? In your City, would a series of pressure monitors and a plan of isolate be more effective than the cost of wholesale backflow preventer instalation, testing, inspection, repairing and education?

In our case the police, public works staff, bylaw and the fire department were integral in providing isolation of the system and frantically ordering residents to cease watering operations. I can go on and on, if you wish you can email me for more information and perhaps I may be of some assistance to your organization.





KRS Services

http://www.krs-services.com

 

[okieduck]

KRS Services,
Yes, I would like more correspondence with you. My city's server is retarded, so I can not directly click to your e-mail link. If you could provide me with that, I will talk to you soon.
Thanks again!
Joy

 

[KRSServices]

Joy,

I've heard of slow servers, but never one that is certifiably retarded.

My email is sobole@telusplanet.net

My website is

http://www.krs-services.com

KRS Services

http://www.krs-services.com

 

[okieduck]

Hello All!
This is to update all who are interested. Our city has decided to provide the option of a detector check out by the curb in a can and a double check in the building. If a business can afford it, they can go with the existing option of a double check detector in a concrete vault by the curb.
Now another interesting dilemma.....
Does anyone know what % of flow goes through the bypass line versus the DCD? We have a case of massive unauthorized water use and we are trying to get an idea of the exact amount used.
Thanks again to all for the help.

 

[KRSServices]

Okieduck,

Thanks for the update. REgarding the unauthorized use, the bypass line should be valved off, therefore no flow should be permitted.

Unless you have thoroughly evaluated your system, I would be careful with the use of the term "unauthorized", because quite often, "unauthorized" can be replaced with "unaccounted", "system losses", "leakage", "mis-calibrated meters" and "theft". Unless you have completed an accurate system evaluation study, complete with balances to confirm results, it may be premature to label as unauthorized use.

I was a municipal manager for 10 years, and worked with water systems for 7 years prior and therefore can speak from experience. If unauthorized use is building specific, or area specific, it can be quantitatively established with a little innovation, detective work and intuition, but must be compared with the system behaviour to provide valuable insight.

KRS Services

http://www.krs-services.com

 

[hydrae]

okieduck
In my observations during system filling through detector checks.
At low flows all the water goes through the bypass meter, since the check valve inline with the meter is easier to open than the big valve (up to 1/4 to 1/2 the rated flow of the meter), at which point the large check starts to open, then the bypass meter slows down and can stop completely. As the flow continue to increase the meter may start again depending upon the design of the big check valve.
So if you have a large reading on the bypass meter, it could be a small leak in which all the water is metered, a medium to large leak which could be 10 to 100 times the reading
I would suggust more investigation, if it was a leak somebody fixed it, if it was somebody washing down the parking lot there may be evidence of that. If it was a large flow, then it may show up on the supply metering or a recording of the distribution pressure
Hope this helps

Hydrae

 

[okieduck]

Hello,
Hydrae, you are correct. We have contacted an engineer from Ames Fire Protection in California and he gave us some helpful info.

Usually, DCDAs are required to carry a minimum flow of 3 gal/min through the bypass line. A flow higher than that usually opens the check valves. However, after a flow of approximately 8-10 gal/min, the flow is completely through the main check valve body.

This is where I get frustrated. The flow detected through the meter is too much to be a leak, because if it was, they would be swimming in it by now. But the guys who go out an read the meter wont investigate it. "yep, its still got a reading ."

Not really wanting a suggestion for the last part, just venting. Thanks again for all your interest and help.
Joy