Backflow Prevention: Let the Civil Engineer Deal With It

Safe-T-Cover
May. 8, 2017
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
Backflow Prevention: Let the Civil Engineer Deal With It
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Backflow Prevention: Let the Civil Engineer Deal With It

Editor's Notes

  1. Backflow prevention at the containment or premise isolation level is controversial in plumbing circles. The Isolation doctrine asserts that we can take care of any cross connection contamination risks by enforcing the plumbing code. Simple as that. The Containment advocates, namely, the AWWA, say, no, that’s not good enough because of unknown changes to individual plumbing systems after the C of O is issued. The Good news is I AM NOT HERE TO SETTLE THE ISSUE! Instead, knowing that these doctrines exist whether we like it or not, I am here to offer some guidance: because the only mistake you can make if you find yourself in a district that requires a containment system is to treat it as another indoor plumbing fixture.
  2. The bottom line: Water districts need premise isolation, and Premise isolation design specifications need to be provided for civil engineers.
  3. Today we’ll cover Design differences DC vs. RPZ; Why it matters Current placement practices and the problems with each The real flood risks of indoor RPZs? The real cost of indoor containment? The explosive growth of the RPZ and how it impacts M/P Es What are the “Best practice” examples around the U.S. for containment BPAs? How do we encourage transitioning this task to the civil engineering discipline?
  4. But now, many purveyors are requiring RPZs on all premise isolation systems. Moreover, as the system designer, a designer may choose to specify an RPZ regardless of the minimum requirement named in the local code. There is no penalty for providing the higher degree of protection.
  5. The Double-check assembly- developed 1950s, works well. Any time pressure on the property (downstream) side exceeds pressure on the city (public) side, - valves close and water stops flowing backwards. Keep in mind, no remedy exists in the event of malfunction of the valve closure or if debris in the water line causes the valves to not close completely.
  6. The Reduced Pressure Zone Assembly Consists of 2 independently operating check valves just like the Double check plus a hydraulically operated differential relief valve located below the first check valve. This hydraulic valve and it’s placement, makes the RPZ virtually fail-safe.
  7. Its really quite elegant, but it comes at a cost to area around the device. * When a Back-siphon event occurs, both check valves close. At that moment, THE RELIEF VALVE will open every time and evacuate the water between the valves. Some think that that event defines the limit of what water can ever flow into a drain. Not so.
  8. Consider a flow-stop situation, one that might naturally occur at the end of the day. If you look closely, you can see that a small pebble has lodged in the #2 check valve. Now let’s say there’s a fire around the corner that causes back siphon at this point in the system. Because the # 2 check valve is not closing, all the water that has been delivered to the building will continue to flow out the relief valve until the private lines are cleared. If this is a four story building, that’s a lot of water.
  9. Failure of # 1. undetected in normal conditions.
  10. Faulire of #1 PLUS Relief valve blockage:
  11. * This picture was tweeted this summer by a Nashville backflow tester. (READ)
  12. There are three options for backflow preventer placement. 3 possibilities, all three are widely practiced.
  13. There are three options for backflow preventer placement. 3 possibilities, all three are widely practiced.
  14. There are three options for backflow preventer placement. 3 possibilities, all three are widely practiced.
  15. There are three options for backflow preventer placement. 3 possibilities, all three are widely practiced.
  16. There are three options for backflow preventer placement. 3 possibilities, all three are widely practiced.
  17. There are three options for backflow preventer placement. 3 possibilities, all three are widely practiced.
  18. There are three options for backflow preventer placement. 3 possibilities, all three are widely practiced.
  19. There are three options for backflow preventer placement. 3 possibilities, all three are widely practiced.
  20. So if these things are designed to dump water, then drain capacity is the issue. The chart on the left is from Wilkins. It’s the Relief Valve Discharge Rate chart of its top of the line, 375 RPZ. It illustrates the flow rate of that device in various sizes and at various pressures. Note that a 2 1/2 inch device will flow 375 GPM at 85 PSI. If you remember your fluid volume tables, you’ll recall that a 4” drain pipe with a 6 inch fall per 100 horizontal feet evacuates clean water at a rate of 93 GPM. If that device is flowing at 375 GPM and your clearing 93, then you are flooding at a rate of 282 GPM. The chart on the right is a Drain Requirements chart created by the city of Columbus, OH. It’s importance cannot be overstated. It reveals that unless you intend to utilize 8” drain pipes at a 6” per 100 horizontal feet fall-rate all the way to the sewer, you cannot justify anything larger inside than a 2” RPZ inside. * An article published this summer in the Chicago chapter of the American Society of Plumbing Engineers written by David DeBord, a former president of that organization, states all these facts better than I can. He uses the Manufacturer’s data supplied by the Watts Corporation and he uses a 65 PSI instead of my 85, but he actually does the math in the article and offers FLOOD rates or 219 GPM for 2 1/2 and 3”; and flood rate of 482 GPM for 4” and above. * He concludes that regarding indoor RPZs, : (READ)
  21. So if these things are designed to dump water, then drain capacity is the issue. The chart on the left is from Wilkins. It’s the Relief Valve Discharge Rate chart of its top of the line, 375 RPZ. It illustrates the flow rate of that device in various sizes and at various pressures. Note that a 2 1/2 inch device will flow 375 GPM at 85 PSI. If you remember your fluid volume tables, you’ll recall that a 4” drain pipe with a 6 inch fall per 100 horizontal feet evacuates clean water at a rate of 93 GPM. If that device is flowing at 375 GPM and your clearing 93, then you are flooding at a rate of 282 GPM. The chart on the right is a Drain Requirements chart created by the city of Columbus, OH. It’s importance cannot be overstated. It reveals that unless you intend to utilize 8” drain pipes at a 6” per 100 horizontal feet fall-rate all the way to the sewer, you cannot justify anything larger inside than a 2” RPZ inside. * An article published this summer in the Chicago chapter of the American Society of Plumbing Engineers written by David DeBord, a former president of that organization, states all these facts better than I can. He uses the Manufacturer’s data supplied by the Watts Corporation and he uses a 65 PSI instead of my 85, but he actually does the math in the article and offers FLOOD rates or 219 GPM for 2 1/2 and 3”; and flood rate of 482 GPM for 4” and above. * He concludes that regarding indoor RPZs, : (READ)
  22. So if these things are designed to dump water, then drain capacity is the issue. The chart on the left is from Wilkins. It’s the Relief Valve Discharge Rate chart of its top of the line, 375 RPZ. It illustrates the flow rate of that device in various sizes and at various pressures. Note that a 2 1/2 inch device will flow 375 GPM at 85 PSI. If you remember your fluid volume tables, you’ll recall that a 4” drain pipe with a 6 inch fall per 100 horizontal feet evacuates clean water at a rate of 93 GPM. If that device is flowing at 375 GPM and your clearing 93, then you are flooding at a rate of 282 GPM. The chart on the right is a Drain Requirements chart created by the city of Columbus, OH. It’s importance cannot be overstated. It reveals that unless you intend to utilize 8” drain pipes at a 6” per 100 horizontal feet fall-rate all the way to the sewer, you cannot justify anything larger inside than a 2” RPZ inside. * An article published this summer in the Chicago chapter of the American Society of Plumbing Engineers written by David DeBord, a former president of that organization, states all these facts better than I can. He uses the Manufacturer’s data supplied by the Watts Corporation and he uses a 65 PSI instead of my 85, but he actually does the math in the article and offers FLOOD rates or 219 GPM for 2 1/2 and 3”; and flood rate of 482 GPM for 4” and above. * He concludes that regarding indoor RPZs, : (READ)
  23. There are three options for backflow preventer placement. 3 possibilities, all three are widely practiced.
  24. the average floor area required for a conventional 3” backflow preventer is 33.325 SF.
  25. Assuming a discount rate of 9%, rent value of $30 per foot annually, and a 25 year life, the net present value of that space to your client is $12, 156.48.
  26. Cost of an enclosure, 2 options: Option 1: conventional, “in-line” assembly= $3,266 Option 2: N-type assembly=$1,100.
  27. Costs are $3,920 and $6,266 respectively.
  28. So the answer to the question is absolutely not: The owner is extremely persuaded to move this thing outside and add additional rent revenue to the enterprise. Moreover, there are a few scenarios that compound this cost differential. It is the likelihood that either of two future events will require the assembly to be upgraded to an RPZ – an outcome that is becoming quite common, and will cost your client thousands of dollars in retrofit expense plus the continued lost opportunity cost from an oversized mechanical room because either, the tenancy will change from low hazard to high hazard through the normal leasing and re-leasing process; or the purveyor will change its definition of what constitutes ‘high hazard’ and your now low hazard user will be re-classified as a high hazard user at a later time.
  29. So what’s happening around the country that might help us understand where all this is going? * We’ve been watching Northern Illinois. More specifically, the 7 most populous cities around Chicago. * It all started in the fall of 2012 with Elgin. On October 24, 2012, they amended their domestic water service requirements as follows: (READ) *A few weeks later, the city of Chicago amended their fire line guidelines as follows: READ * Not to be left behind, in January of 2013 Naperville saw Elgin and raised them one, amending their guidelines to require RPZs on all commercial and and multi-residential new construction for each service, Fire, irrigation, and domestic.
  30. Within the Central Ohio area, Columbus has articulated a rational middle-ground position for getting Backflow preventers out of harm’s way. Recognizing that drain capacities for small sized RPZs CAN be accommodated with a typical 4” drain system, they detailed two methods of RPZ placement, one indoors for small RPZs, and one outdoors for larger sizes. * The drawings for the indoor method explicitly address drain system requirements and force designers to reconcile the flood rate risks with specific drainage system capacities * And the outdoor method mandates an enclosure that is ASSE-1060 compliant.
  31. Within the Central Ohio area, Columbus has articulated a rational middle-ground position for getting Backflow preventers out of harm’s way. Recognizing that drain capacities for small sized RPZs CAN be accommodated with a typical 4” drain system, they detailed two methods of RPZ placement, one indoors for small RPZs, and one outdoors for larger sizes. * The drawings for the indoor method explicitly address drain system requirements and force designers to reconcile the flood rate risks with specific drainage system capacities * And the outdoor method mandates an enclosure that is ASSE-1060 compliant.
  32. Delaware, Ohio. In the 2013 release of their Infrastructure design guide, they now mandate RPZs in outdoor enclosures on all commercial, industrial, and institutional water lines.
  33. Fort Worth, TX. Just a few months ago, Fort Worth updated their Design Standards Manual. Within it, they’ve defined what we’re calling the Tenant Provision. [READ]
  34. In Central Virginia, the city of Lynchburg was one of the earliest adopters of the current trend toward RPZs. In 2008, they amended their construction guidelines as follows: [READ]
  35. In the Mountain West, Denver, Colorado has long had the reputation of being a leader in infrastructure quality: In 2012 and 2013, Denver Water, one of the nation’s largest water purveyors, added specifications and drawings for above ground backflow preventer enclosures to their standard details. They make specific recommendations about 3” and larger RPZs and even small double check backflow preventers being deployed to aboveground enclosures.
  36. All these cities have made changes whereby RPZ use has been expanded either by lowering or eliminating the hazard threshold for use on domestic water lines in the past 5 years.
  37. Consider the ‘worst case scenario’ of a water volume discharge of a containment backflow prevention, namely, an uncontrolled discharge caused by a failure of the #1 check valve contemporaneous with the relief valve being stuck or propped open by debris. If there is no faucet demand within the commercial premise, such as over night, then this perfect storm produces an unmitigated flow of all available water through the relief valve continuously. The management of this sudden water deluge is a significant hazard. As severe as the most severe storm water runoff event. This hazard is clearly work found within the civil engineering discipline rather than the plumbing engineering discipline. Designing and specifying any outdoor containment BPA – even if it is placed within the jurisdictional boundaries of the plumbing engineer, is asking for trouble.