Backflow Best Practices and Standard Details: Part 1

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Part 3: The Differences Between DC & RPZ Backflow PreventersPremise Isolation Backflow Prevention: Best Practices & Standard Details

Premise Isolation: Best Practices & Standard Details.Definitions and term use:

Isolation backflow prevention: In addition to the lavatory and water fountain, most buildings plumbing systems include fixtures that are designed to clean contaminated equipment, carbonate beverages, and even infuse chemicals and detergents. Many of these processes create dangerous and toxic substances. If these substances were allowed to reverse back into the buildings fresh water piping, an event known as backflow, it would create serious health hazards for the individuals on site. Building authorities deal with these risks by specifying appropriate backflow preventer assemblies at those specific locations where contamination is a risk. The term for this solution is isolation backflow prevention because a special plumbing apparatus known as a backflow preventer isolates high-hazard fixtures and equipment at the point of use from the rest of the on-site piping system.

.Definitions and term use:

Containment or Premise Isolation backflow prevention: For public water systems, water that has been delivered through its water meter to a water customer is only done safely and responsibly when there is no possibility that that water will return back from the customer to the water system, an event (also) known as backflow. Disparate groups within plumbing, design, and water management have devised their own favorite terms for this system. The plumbing community prefers Containment backflow prevention because such systems contain delivered water at the subscribers premises; On the other hand, water districts tend to prefer Premise Isolation. It is important to understand that whether called Containment or Premise Isolation, we are referring to the task of eliminating backflow at the Point of Supply from the public water system.

This presentation is limited to the recognized best practices of these containment or premise isolation systems.Premise Isolation: Best Practices & Standard Details

Introduction

The water engineering community has been struggling with new professional liability risk involving the location of premise isolation backflow preventer systems; Not because of new design practices, but because of new information about the old practices. There has been a slow trickle of warnings for years, but in the past 3 years important organizations and industry leaders have added new warnings with much stronger language that not only change recognized best practices, but actually challenge the fitness and safety of older placement methods altogether.

Premise Isolation: Best Practices & Standard Details

The Eng commty: struggling w/ new professional liability risk involving the location of PremISO Backflow preventer systems. not because new design practice, but because of new information about the old practices.

Slow trickle of warnings for years,

* past two years: imp orgs and indry leaders have added new warnings, much stronger lang: not only change recognized best practices, but actually challenge the fitness and safety of older placement methods altogether.

IntroductionCan we rid ourselves of the problem by dumping the system itself?

Sadly, we are learning through SCADA and AMI that there is actually more backflow occurring at the premise than we previously suspected.


Can we rid ourselves of the problem by dumping the system itself?More backflow is occurring than was previously believed

Introduction

With this new risk realization comes a new interested party: The insurance company. Because of this very public commentary from experts and leading groups, casualty carriers, through subrogation, have new weapons for damage recovery. And anytime the accused designer is able to demonstrate that local government contributed, whether materially or passively, to the poor design, the water district and/or building authority may be at risk for the liability.Premise Isolation: Best Practices & Standard Details

And with this new risk realization comes a new Interested Party. The insurance company.

Because of this very public commentary from experts, they now have new weapons for damage recovery.

And anytime the designer is able to demonstrate that local government was causal to the poor design, they, through the magic of subrogation, have at least one more pocket to pick.

* The Local Water Authority.

Assuming the legal rights of a person for whom expenses or a debt has been paid. Typically, an insurance company which pays its insured client for injuries and losses then sues the party which the injured person contends caused the damages to him/her.Introduction

Because of subrogation, the water district needs to demonstrate that no unsafe methods are promoted by their plans review teams. The best way to demonstrate that is with published standard details and drawings that are consistent with recognized best practices.


IntroductionMeanwhile, at the 2016-17 bi-annual conference of the American Society of Plumbing Engineers, one popular learning module titled Let the Civil Engineer Deal with the Containment Backflow System suggests that leadership is seeking reassignment of the premise isolation backflow system design to the civil discipline. No surprise, other than how long it took to realize Plumbing engineers have nothing to gain and everything to lose when they specify indoor RPZs becauseThe flood risks now being realized from indoor installations of RPZs is extraordinary;Designing for outdoor placement includes grading and surface contouring for sudden flood water flows; a task that is beyond the scope of a plumbing engineers training or expertise.Premise Isolation: Best Practices & Standard Details

MEANWHILE, In the October Bi annual conf of the ASPE, Plumbing engineers are seeking reassignment of the Prem-Iso BP system design to the civil discipline due to

1. the flood risks now being realized from indoor installations of RPZs;

2 .the realization that designing BPAs for outdoor placement includes grading and surface contouring for sudden flood water flows which are beyond the scope of a plumbing engineers expertise.

Introduction

According to a survey of 1220 U.S. civil and plumbing engineers conducted over a 19month period, 3 out of 4 say they need local water authorities to provide standard details for outdoor aboveground backflow preventer systems.You can read more about the results of this survey here.Premise Isolation: Best Practices & Standard Details

According to a survey of 1220 civil and plumbing engineers in North central Texas

conducted over a 19month period, 3 out of 4 say they need local water authorities to provide standard details for outdoor aboveground backflow preventer systems.

Water Districts NEED Premise Isolation in order to fulfill their EPA mandate; andIntroductionBottom Line:

. The return of any water to the public water system after the water has been used for any purpose on the customers premises or within the customers piping system is unacceptable and opposed by AWWA.

Premise-Isolation design details and specifications need to be provided to civil engineers because of their general familiarity with standard details and their comparable lack of familiarity with backflow systems.AWWAs preamble to the Cross Connection Control Manual, published by EPAPremise Isolation: Best Practices & Standard Details

The bottom line: Water districts need premise isolation, and

Premise isolation design specifications need to be provided for civil engineers.

Water utilities are seeking more premise-isolation. That more containment systems are being specified as RPZ regardless of hazard threshold.AWWA, ASPE, & the legal community recognize outside aboveground as best practice for premise isolation.

This presentation will showIntroductionPremise Isolation: Best Practices & Standard Details

Consider these facts.

2 types of backflow Preventers:Design differences DC vs. RPZ

Double-Check Valve Assemble, DC or DCDAReduced Pressure Zone Valve Assembly, RP RPDA

A designer may specify one of two types of BFPs for premise isolation. Up until recently, the decision for which assembly to specify was based solely on the perceived hazard to the waste water system created by the processes of the end user. High hazard (better named, high waste-hazard) uses were required to utilize an RPZ. Uses that did not pose a risk to the waste water were allowed to use a DC.

Design Differences DC vs. RPZPremise Isolation: Best Practices & Standard Details

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.

2 types of backflow Preventers:Design differences DC vs. RPZ


Design Differences DC vs. RPZFor example, a medical facility or a chemical plant triggered the requirement for an RPZ while an office or simple retail user would be allowed to use a DC or, depending on the municipality, no premise isolation system at all.

Now, as we will discuss below, many purveyors are requiring RPZs on all premise isolation systems because of the inherent limits of protection provided by the double check valve for the public water supply. Premise Isolation: Best Practices & Standard Details


DC: Low hazard?

Public (Supply) sideProperty(Private) side

FlowDesign differences DC vs. RPZDesign Differences DC vs. RPZThe Double-check assembly was developed in the 1950s for the fire industry. And for many years it was regarded as a satisfactory solution. The design is simple. Any time system-water pressure on the property (private) side exceeds the system pressure on the city (public) side, two redundant check valves close and water stops flowing backwards. Premise Isolation: Best Practices & Standard Details

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.

DC: Low hazard?Design differences DC vs. RPZDesign Differences DC vs. RPZBut no remedy exists in the event of a malfunction of the valve closures or if debris in the water line causes the valves to not close completely. Additionally, the DC is a closed, or blind system making detection of any failure impossible without a field test performed by a licensed tester. Today, millions of DCs are in service that may have failed. When a Florida city began its annual testing program in 2010, it found 52% of the valves in service had failed with no way to determine how long they had been inoperable.

Public (Supply) sideProperty(Private) side

FlowPremise Isolation: Best Practices & Standard Details

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.

Design differences DC vs. RPZDesign Differences DC vs. RPZRPZ: Fail-safe against returning water

FlowProperty(Private) sidePublic (Supply) sideThe RPZ emerged in the 1970s as a remedy to the double-check limitations. Like the DC, it incorporates 2 redundant check valves. But unlike the DC, the RPZ incorporates a hydraulically operated differential relief valve directly beneath the # 1 check valve. It is this relief valves placement (along with the universal laws of hydraulics) that make this a fail-safe solution for water purveyors. As elegant as the design is, it comes at a cost. And that cost is the surrounding area. Premise Isolation: Best Practices & Standard Details

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 its placement, makes the RPZ virtually fail-safe.


FlowProperty(Private) sidePublic (Supply) sideAs the DC reveals, valves fail. But when they fail in an RPZ, the assembly is designed to create a deluge event directly under the assembly so that no contaminated water returns to the public water supply. Because of the danger of contamination, no water from the relief valve may be piped directly from the assembly. It must release into the atmosphere away from any piping. Watch this short video revealing an actual discharge. Premise Isolation: Best Practices & Standard Details

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 its placement, makes the RPZ virtually fail-safe.

Flow StopDesign differences DC vs. RPZDesign Differences DC vs. RPZRPZ: Fail-safe against returning waterIn a flow-stop situation the water between the check valves will often drain out the relief valve. Some think that that event defines the limit of what water can ever flow into a drain.

Not so.


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.

Loss of pressure

#2 valve blockedDesign differences DC vs. RPZDesign Differences DC vs. RPZConsider 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 lets say theres 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, thats a lot of water!RPZ: Fail-safe against returning waterPremise Isolation: Best Practices & Standard Details

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 lets say theres 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, thats a lot of water.

#1 valve Failure

Normal delivery pressureDesign differences DC vs. RPZDesign Differences DC vs. RPZNow consider a failure of the #1 check valve. Under normal operating conditions, this failure would go unnoticed. After all, water is being called for by the user through the opening of taps. The water flows in undeterred.

But with this imbalance in the system, changes in demand tend to rock the remaining valves open and closed sporadically. RPZ: Fail-safe against returning waterDemandPremise Isolation: Best Practices & Standard Details

Failure of # 1. undetected in normal conditions.

#1 valve FailureBlockage relief valve


DemandNormal delivery pressureThis creates the conditions for the perfect storm scenario. The imbalance created by the # 1 failure makes the relief valve more prone to opening momentarily, allowing debris to block the closure of that valve.

Under such conditions, a constant flow of delivered water will begin to flow directly out the relief valve. This reduces water pressure for the user, but delivery will continue.Premise Isolation: Best Practices & Standard Details

Faulire of #1 PLUS Relief valve blockage:

Design differences DC vs. RPZDesign Differences DC vs. RPZ

No demandNormal delivery pressureRPZ: Fail-safe against returning waterThe real damage begins when the user stops using water such as at the end of a work day.

With the relief valve blocked open and the # 1 valve inoperative, all the water that the purveyor can provide will flow unabated out the relief valve wherever it might be, and continue until the water source is interrupted.

This is the scenario that must be avoided: the perfect storm.Premise Isolation: Best Practices & Standard Details

* This picture was tweeted this summer by a Nashville backflow tester. (READ)

Design differences DC vs. RPZDesign Differences DC vs. RPZRPZ: Fail-safe against returning waterThis picture was tweeted last summer by a Nashville backflow tester. He was called to a multi-story office building on a Sunday to inspect a malfunctioning backflow preventer. By the time he completed his service of the assembly, a small pebble was all he recovered from the 8 RPZ in the background. Premise Isolation: Best Practices & Standard Details


Design differences DC vs. RPZDesign Differences DC vs. RPZRPZ: Fail-safe against returning waterThis was the scene when he arrived.

By the way, the RPZ was working perfectly before and after the call, behaving precisely as it was designed to. Premise Isolation: Best Practices & Standard Details


Design differences DC vs. RPZ


Safe-T-Cover has put together an easy to reference guide on the differences between double checks and reduced pressure zone backflow preventers on their blog.Design Differences DC vs. RPZPremise Isolation: Best Practices & Standard Details


The public water supply is unprotected from returning water without a premise isolation system. RPZs are only fail-safe solution.The duties of the building/plumbing authority and the plumbing code do not wholly satisfy the duties of the water utility. Indoor RPZs 3 and larger are perpetual floods risks.The need to address sudden on-site water flows disqualify MEPs from outdoor premise isolation design, even if within MEP halo. Civil engineers are unfamiliar with BPA installations and need standard details from water authorities.Take-AwaysA broadly adopted region-wide set of guidelines would save cities 100s of hours in plans-review time.Premise Isolation: Best Practices & Standard Details

1.2. Strong natl migration toward RPZ, away from DC with many standard details that have ceased to iteratively improve. Thats a business school way of saying Best practices are now evident because as time continues, cities are defining the same methods.3. Indoor RPZ 2 and larger cause floods and feed insurers. Its not enough to say that some large indoor systems are poorly designed. If your building has a flange-sized RPZ inside and does not have at least an 8 drain system all the way to the sewer, then it fails the flood liability test and should not be there.4. MEP engineers cannot stamp anything that is to be installed beyond 6 of the building envelope so how can they design flange-sized RPZ systems at all?5. Civil Engineers are not plumbers and need standard details provided by water authorities in order to properly design these systems.6. Water authorities are driving these devices inside because thats the way everyone knows how to do it. Continuing to direct and favor methods that are unsafe, or even less safe, expose the jurisdiction to liability risk.

Safe-T-Cover's blog: Updated weekly with articles on backflow prevention, standard details, and best practices. Enclosure Design eBook: Learn the 5 design considerations for aboveground enclosuresRecent story on decision to add standard details by the city of Arlington, TexasTrends in Backflow Preventer Installation: A downloadable guide to the latest trends in backflow best practices.Additional ResourcesPremise Isolation: Best Practices & Standard Details

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Backflow Best Practices and Standard Details: Part 1

Engineering

Transcript of Backflow Best Practices and Standard Details: Part 1