RP/DC Assemblies

ASSE 1013, Reduced Pressure Principle Backflow Prevention Assemblies (RP);

ASSE 1015, Double Check Backflow Prevention Assemblies (DC);

ASSE 1047, Reduced Pressure Principle Detector Backflow Prevention Assemblies (RPDA);

ASSE 1048, Double Check Detector Backflow Prevention Assemblies (DCDA)

If you live in an urban area, chances are that the water you drink has passed through an RP or DC assembly. Aside from an air gap, these backflow prevention assemblies provide the best all-around backflow protection against backpressure and backsiphonage. In each issue of Working Pressure magazine, we will be looking at a different set of ASSE product performance standards that have a critical effect on improving public safety, why these standards and products are important, and what the standards cover.

Let’s review, at a basic level, what RP and DC assemblies are, per ASSE’s standards:

Reduced pressure principle backflow prevention assemblies (RPs or ASSE 1013s) consist of:

• Two independently acting check valves in series, force-loaded to a closed position;
• A hydraulically operated, relief valve force-loaded to an open position, oriented between the checks;
• Two resilient seated shut-off valves on either end of the assembly; and
• Four properly located test cocks to measure various pressures

Double check backflow prevention assemblies (DCs or ASSE 1015s) consist of:

• Two independently acting check valves in series, force-loaded to a closed position;
• Two resilient seated shut-off valves on either end of the assembly; and
• Four properly located test cocks to measure various pressures

If a bypass line bypasses the checks, and on that line is a water meter and smaller backflow assembly of similar design, now you have an RP detector assembly (RPDA or 1047) or a DC detector assembly (DCDA or 1048). If the bypass line only bypasses the downstream check (check valve #2), and includes a meter and a single check, now you have a RPDA Type II or DCDA Type II. It should be noted that an RPDA can function as an RP and, similarly, a DCDA can function as a DC – the requirements are the same except for the needs of the detector assemblies.

Note on air gaps: Creating or installing an air gap is the safest, most inexpensive, and most conservative means of backflow protection. (Air gaps comply with ASME A112.1.2 and air gap fittings comply with ASME A112.1.3). They are generally mentioned in the same breath as a 1013 or 1047 assembly when citing proper backflow protection. However, while these are excellent for drainage or filling open tanks, they are open to the atmosphere by design and therefore do not have the ability to maintain line pressure during no-flow situations.

Backflow Preventer Failure Mechanisms
When we refer to backflow protection, we are protecting against two scenarios in which backflow could occur, where the outlet pressure exceeds inlet pressure. How can this happen? Some examples:

1. Upstream inlet pressure is reduced below 0 psig resulting in backsiphonage:
   1. A large flow can draw water from both the system inlet and upstream of a fitting or assembly. This can occur both inside a premises (e.g. quickly filling a reservoir) or outside (e.g. breaking water main).
   2. Similarly, a portion of an in-between system branch is isolated with shut-off valves and is drained for maintenance. After completion, the downstream shut-off valve is opened first.
   3. Water flow across the co-linear portion of a tee connection can result in a Venturi effect, creating a vacuum at the third, smaller-diameter connection of the tee.
2. Downstream outlet pressure is increased to be greater than the upstream inlet resulting in backpressure:
   1. A pump is added to a system at one inlet and one of the downstream connections is also connected to a system inlet.
   2. Inlet and outlet connections are reversed on a pump.
   3. An elevated hose or vertical water pipe can also create backpressure by gravity. One foot of water column is equivalent to 0.43 psi (2.96 kPa) of pressure.

When designing a plumbing system (or a product), part of good design practice is looking back and performing a Failure Modes and Effects Analysis (FMEA) to see where a potential problem may arise. Central to this is evaluating the severity, occurrence, and ability to detect the problems should they arise. The severity of the ramifications of having a backflow incident is by default the most severe given the health concerns. Prior to backflow incidents happening, backflow causes are generally undetectable, even though there is the Authority Having Jurisdiction’s (AHJ’s) initial inspection and annual in-service tests required for backflow preventers. For example, consider how easy it is to leave the end of a garden hose connected to concentrated herbicide. The occurrence of backflow on a system can be high as cross-connections can be made by the general public. Even trained professionals can make an honest mistake. Hence, it is absolutely critical that the assemblies be compliant with ASSE standards and be annually tested by certified individuals.

Requirements
ASSE’s standards for both RPs and DCs represent the cumulative knowledge from a diverse set of backflow prevention experts, along with consideration for other standards and documents. This ensures that ASSE has the strictest backflow prevention standards for these assemblies. For example, all assemblies are first required to undergo a hydrostatic pressure test before even going through any of the dynamic tests. This is particularly conservative, as most standards for other plumbing products consider hydrostatic tests to be safety tests, checking for catastrophic failures. In our case, a catastrophic failure is a backflow situation in the field.

Since these products are present as containment assemblies at the point-of-service to a premises at the water meter and internal point-of-use protection known as isolation, pressure loss needs to be minimized across the assembly with minimum flow capacities defined by ASSE standards. If the products are installed on fire lines, AHJ’s may require a detector assembly to be present by way of an RPDA or DCDA so that the fire department is informed if a sprinkler is activated. ASSE 1047 and 1048 cover the requirements for that scenario.

On an ASSE 1013 or 1047 backflow prevention assembly, if the downstream #2 check fails, the relief valve vents water until the outlet pressure is at least 2 psi lower than the inlet. If the relief valve fails, the upstream #1 check can still provide protection.

There are several other performance requirements to which the assemblies need to be able to demonstrate compliance, including:

• At what pressure the relief valve activates on RPs and RPDAs;
• Whether the assembly can withstand the extreme temperatures and pressures seen in the field;
• If the assembly can withstand a hydrostatic test to 4x the rated pressure as a safety test;
• The drip tightness, hydrostatic backpressure, seat adhesion, and independence of each check;
• Pass a combination backpressure and backsiphonage situation; and
• Pass a 5,000-cycle max-min pressure variation (life cycle) test

Upcoming Revisions
In the coming months, there will be a new set of revisions to these standards such that these requirements will be reviewed again to ensure they are the strictest of any backflow standards or documents. At time of writing, the working group to revise ASSE 1013, 1015, 1047, and 1048 is reviewing the final set of revisions.

This consensus-based working group is comprised of various manufacturers, contractors, the University of Southern California Foundation for Cross-Connection Control and Hydraulic Research, and ASSE International. The working group’s goal is to compare the current set of standards with that of the existing body of standards and documents to ensure that ASSE has the strictest criteria. These revisions are going to be a major upgrade to align and improve requirements for the benefit of the public. Look for them in the coming months.

Standards in the Model Codes
Assemblies that comply with ASSE 1013, 1015, 1047, and 1048 are required for various locations in a plumbing system and fire sprinkler system. RPs and air gaps are the most common and best methods of backflow protection. On the following page is a chart that covers the various locations for which RPs and DCs are appropriate for use as referenced by the Uniform Plumbing Code^® (UPC) and the International Plumbing Code^® (IPC).

Part of the consideration as to which backflow assembly to use for which category is the potential downstream hazard. For example, fire sprinkler systems may use potable water to fill in the sprinkler system lines. These systems are stagnant over time as one huge “dead leg.” This is a non-health affecting or low hazard situation that requires high rates of flow when needed, so a DC or DCDA is appropriate. However, some fire sprinkler system designers add antifreeze or fire-retarding chemicals to the system water. Now that water is a health affecting or high-hazard fluid that requires use of an RP or RPDA.

Note that low-hazard refers to water pollution (smell, taste, turbidity, etc. are affected) and high-hazard refers to water contamination (resulting in negative health effects). The decision as to which substances or situations are low- or high-hazard and the backflow protection that is permissible is decided by the model codes’ technical committees and local AHJs. In the UPC, table 603.2, and in the IPC, table 608.1, hazard levels for each backflow prevention assembly are defined.

Install, Test, and Repair
A key complementary portion to these assemblies is the ability to properly service the products in the field to help ensure safe delivery of potable water. ASSE/IAPMO/ANSI Series 5000, Cross-Connection Control Professional Qualifications Standard, defines the requirements for the individuals who install, test, and repair backflow protection assemblies. Both the UPC and the IPC reference following ASSE 5013, 5015, 5047, and 5048 for testing RPs and DCs (UPC 603.4.2, IPC 312.10.2). In each of those standards, it’s stated that at a minimum, backflow prevention assemblies shall be tested upon installation, annually, and immediately after repair or when returned to service. The UPC further states that the test “shall be performed by a certified backflow assembly tester or repairer in accordance with the ASSE Series 5000 or as approved by the AHJ.”

If you would like more information, feel free to contact ASSE at staffengineer@asse-plumbing.org. You can also find me at the ASSE International Mid-Year Meeting, held April 10-11 at the ASSE International office in Mokena, Ill.