For the past several years, there has been quite a debate about the need for backflow preventers on fire protection systems. This debate culminated in an American Water Works Association (AWWA) study published in 1998. The purpose of this article is not to expand on that study, but to pick up with design requirements of backflow preventers, specifically those meeting ASSE 1013, 1015, 1047 and 1048 and discuss improvements for fire protection systems. The American Society of Sanitary Engineering (ASSE) is an ANSI accredited standards writing organization, and with that accreditation comes the responsibility of a five-year review of standards to see if they are current or need to be updated.

Because of all the controversy in the past several years on backflow protection on fire sprinkler systems, a list of industry concerns from the fire industry has been developed with respect to the use of backflow preventers on these systems. The list of issues centers around the main question of whether current standards were written with the application of fire sprinkler systems in mind. I think the answer to this question is that current backflow preventers do indeed work on fire sprinkler systems. However, when the standards were developed, no special consideration was given to the operating modes of these fire protection systems. It is therefore important in ASSE's review of these backflow standards that they now take very seriously the concerns that have been voiced by the fire protection industry. The list of concerns can be summed up as follows:



Ease of installation

Pressure drop

Reliability and full flow capacity after extended static periods

Effects of backflow preventers during alarm testing

Relief valve discharge, both during the static as well as the flowing condition

Over the past 1-1/2 years, an ASSE working group has been reviewing these concerns, along with others in a review of the subject ASSE standards. Probably the most significant action that the working group took was to agree that there was a need to consider the special needs and use of backflow preventers in fire protection systems. And, in fact, the group agreed to create a new classification of devices for reduced pressure principal, double checks, detector check assemblies, double check detectors, and reduced pressure detector assemblies. These products would receive the suffix "F" (e.g., RPF, DCF, DCDAF and RPDAF).

If we look back to the list of concerns, I would like to take them in order and discuss how they have been specifically addressed by the proposals from the current backflow working group.

Cost, Size and Ease of Installation

Items 1, 2 and 3 can actually be lumped together. In general, these issues are adequately handled by the existing standards, in that they are performance based standards with very little prescriptive language on the physical design of the backflow preventers. As the needs and concerns of the fire protection industry have been made known, several manufacturers have responded with new and improved models. Specifically we now see backflow preventers that are lightweight due to either fabricated bodies or ductile iron castings. We now see the use of major plastic components in the large flanged backflow preventers as well as backflow preventers that are capable of various types of installations, such as vertical up or vertical down, or combinations of both. I think this manufacturing innovation speaks well for ASSE standards in terms of their being performance rather than prescriptive standards.

One specific item that the working group addressed allowed for cost savings on detector assemblies. The group agreed that the bypass lines, which now bypass both the first and second checks, can simply bypass the second in both the RPDA as well as the DCDA, and the bypass line needs to configured with a new testable single check. Currently, the standards require a complete backflow assembly in the bypass line, which is obviously more costly than the newly proposed testable single check.

Another advantage for this arrangement is that the bypass assemblies for the RPDA and the DCDA actually will be identical assemblies, since they are bypassing the second check on both valves. Also, since they are bypassing only one check, there is less variation in static head loss across the mainline assembly, which means greater precision can be used in using the proper spring load for the bypass line. This can result in lower overall static head losses in the assemblies.

Pressure Drop

Item 4 concerns the pressure drop presented by backflow preventers. Single check valves, which have commonly been used in fire protection systems, have static head losses as low as 1 psi and head losses at full flow as low as 3 psi. In order to address this issue, the backflow working group is proposing to reduce the spring load on double checks and the second check of reduced pressure devices from the current 1 psi to 1/2 psi, and on the reduced pressure principal backflow preventers to allow the relief valve opening point to approach 1 psi. Individually looking at these, it doesn't seem as though it would amount to much, but let's look at each type of valve specifically and what this small change in the spring load can accomplish.

On a double check valve, the current standard requires 1 psi in each check valve. But in reality, since field testing procedures are calling for 1 psi in the direction of flow and because purchasers expect this to be true several years after installation, manufacturers are producing valves with spring loads on each check in the range of 1-1/2 to 2 psi. This means that we are looking at a static head loss of 3 to 4 psi before water even flows through the device. If the 1/2 psi is adopted, along with recommendations for field testing with back pressure as opposed to direction of flow, this could allow manufacturers to design their checks as low as 3/4 psi, which would result in an overall static head loss across the complete assembly of only 1-1/2 psi. This is at least a 50% reduction from where we are today.

In the case of a reduced pressure principle device, again we can save as much as 1 psi on the second check. But by lowering the relief valve opening point to 1 psi and replacing the prescriptive 3 psi buffer zone with a performance test, we can accomplish a great deal more. For example, with the relief valve opening point at 1 to 2 psi, the first check valve differential could be as low as 4 psi, and again the second check valve at 1/2 or 3/4 psi at the most, the total head loss across the device now is less than 5 psi. In products currently being produced, it is not unusual to see head losses at static from 8 to 10 psi. Again, we have achieved a 50% reduction in static head loss.

Reliability and Full Flow Capacity

To address item 5, the working group is recommending requiring a seat adhesion test from UL 312, the standard for check valves for fire protection systems. This test insures that during long term static installations, there will be no bonding between the check valve disc and seat, which could result in a delayed or partial opening of the check valve under a fire demand.

To address the further concerns about the checks being affected long term by corrosion or mineral deposits, the working group is recommending two additional tests. The first one is a hot water test that also incorporates a special test water which would rapidly indicate if a product was sensitive to build-up from minerals or calcium deposits. The second test is a life cycle test or, as an alternative, a one-year field test. The life cycle test consists of 5000 cycles during which time it simulates the actual use in a fire protection system, which is basically static with only small flows that would occur during an alarm test cycle, about 50 gpm.

Backflow Preventers & Alarm Testing

Item 6 was a concern that the pressure drop on backflow preventers was giving false readings during a typical alarm test in which a test and drain valve is used which allows approximately 50 gpm to flow through the system. The idea of this test is to simulate one sprinkler head going off and to verify that the alarm will actuate and ring during this test period.

Problems with backflow preventers have been traced to specific styles of backflow preventers that have a sharp decrease in pressure drop once the check valves open. This can be seen quite often in a toggle-style swing check. To test for this condition and verify that it will not occur, we added a requirement in the flow testing that during the first 50 gpm of flow through either a double check or an RP, or a detector assembly, the head loss across the assembly cannot decrease until you are past the 50 gpm. Those who are intimately familiar with this type of problem in the field have agreed that this 50 gpm test will indeed prevent field problems during the alarm testing.

Relief Valve Discharge

Item 7 has been expressed as a concern over nuisance relief valve discharge which results in puddles of water. This, of course, can happen during static conditions with pressure fluctuation. Under the current standard, only 3 psi pressure fluctuation is anticipated, and we all know that fluctuations greater than this occur in the field. Also, several current field testing procedures reference a 3 psi buffer between the relief valve opening point and the first check. Again, this would only protect from relief valve discharge under a 3 psi fluctuation.

To be more realistic, the working group is recommending that the test for relief valve discharge be with a 15 psi pressure fluctuation. But in return, as mentioned under one of the other items, would be the elimination of the prescriptive 3 psi buffer between the relief valve opening point and the first check. If indeed fire protection backflow preventers do not have relief valve discharge regardless of the pressure difference between the relief valve opening point and the first check of up to 15 psi, there is no point in demanding the 3 psi buffer, which simply results in a higher static head loss. Also, it is recommended that during the flow test for all fire protection backflow preventers that the flow be increased up to 150% of the normal rated flow and during this period from 0 to 150% of the flow, there shall be no discharge of water from the relief valve.

It is obvious that the backflow working group has been very hard at work with the special considerations for fire protection. They are to be commended for their work and for their willingness to step out with some rather innovative and creative resolutions to real world problems. These four standards have been approved by a consensus of the Product Standards Committee, and are being submitted to the ASSE Board of Directors for their review and approval. In addition, all four of these standards have been submitted to ANSI to begin the open review process to become American National Standards. I look forward to the year 2000 when manufacturers are actually producing and selling this new classification of fire protection backflow preventers.