A properly functioning RPBA will periodically release small amounts of water due to changes in line pressure up or downstream of the assembly.  For this reason, this type of assembly should be installed in areas that are not subject to water damage and have proper drainage. When backflow happens, a properly functioning RBPA may release some water. If the RPBA becomes clogged by debris or is not functioning properly and needs repair, it may discharge a large volume of water.

The length of the domestic gas hose pipe is not more than two meters, which is to prevent excessive gas storage in the pipe due to the pipe is too long, resulting in pipe corrosion or loose connection and gas leakage.

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The location of the assembly, service size, and hazard level of the connection determine which backflow assembly you should use. If you have questions about which type of assembly you need, contact the Water Bureau Water Quality Inspection staff at 503-823-7480. Below are some assemblies commonly used in commercial applications. More information about the all the following assemblies can be found on our backflow assembly installation requirements page.

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DCDA BackflowPreventer

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The reduced pressure backflow assembly (RPBA) is designed to prevent backflow caused by backpressure or backsiphonage and may be installed on either low- or high-hazard connections. Backsiphonage is when water moves in the direction opposite its regular flow.

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Generally speaking, the price of the gas hose pipe is related to the material and brand, and it is generally calculated together with the installation cost because of the need for professional installation.After installing the natural gas hose pipe, we should pay attention to proper protection, do not seal the gas hose pipe, do not disassemble the gas hose pipe without permission, etc. Now, let’s get to know the knowledge of gas hose pipes!

The double check valve assembly (DCVA) is commonly used to protect against backflow hazards that do not pose a health risk. They may be used under continuous pressure and protect against both backsiphonage and backpressure conditions. They can be installed above or below ground, but no more than 24 inches deep or five feet above the floor or grade.

During normal operation, the pressure between the two check valves, referred to as the zone of reduced pressure, is maintained at a lower pressure than the supply pressure. If either check valve should leak, the relief valve is designed to open and discharge water to the outside.

Some residents choose to install a backflow device on their hose bib. These are called vacuum breakers and they do not need to be tested. You can purchase them at most plumbing and hardware stores.

There are two types of vacuum breakers: the atmospheric vacuum breaker (AVB) and the pressure vacuum breaker assembly (PVBA). The Water Bureau doesn't allow either the AVB or PVBA to be used for backflow protection.

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The length of the domestic gas hose pipe should not be too long or too short. If the hose is more than 2 meters, it will increase the resistance of the intake pipe, reduce the heat flow of the stove, and lead to the loosening of the connection. If the hose is too short, it is easy to pull the phenomenon, resulting in the hose off.

The assembly consists of two spring-loaded check valves, a bypass assembly with a water meter and double check valve assembly, and two resilient seated indicating shutoff valves.

This assembly uses a mainline reduced pressure backflow assembly equipped with two resilient seated indicating shutoff valves, a bypass arrangement containing a smaller reduced pressure backflow assembly, and water meter. The RPDA must be installed at least 12 inches above finished grade or the 100-year flood plain, whichever is greater.

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The AVB is among the simplest and least expensive mechanical types of backflow prevention device that the end user can buy. The PVBA is an outgrowth of the AVB and evolved out of a need to have an atmospheric vacuum breaker that was testable and could be used under constant pressure.

Your plumber or licensed backflow assembly testing company will likely know which type of assembly to use. Backflow assemblies most commonly installed on residential irrigation systems are the double check valve assembly (DCVA) and the pressure vacuum breaker assembly (PVBA). The DCVA may be installed in a vault below finished grade. The PVBA must be installed at least 12 inches above finished grade.

Therefore, for the sake of safety, the length of the gas hose pipe should not exceed two meters, so that the personal safety and hose safety are guaranteed.

One step you can take to protect our drinking water is to keep the ends of hoses out of pools or other containers while you are filling them. For example, if a hose is submerged in the pool, the chlorinated pool water may enter the drinking water system during a backflow condition. When filling pools, keep the end of the hose out of the pool and have a gap between the end of the hose and the surface of the water. This gap must be twice the diameter of the hose and never less than one inch.

According to the regulations, “when the hose is connected to the fuel, the length of the hose should not exceed 2 meters and there should be no joint.” The reason why the length of the gas hose pipe is not allowed to exceed 2 m is to reduce the gas storage in the hose. Because in the process of use, there will be some natural gas left in the gas hose. If the hose is too long, it will not only have corrosion effect on the hose, but also have the risk of gas leakage.

Moreover, it is easy to hook and touch the hose in use, leading to the situation that the connecting part of the hose falls off or becomes loose, then causing the gas leakage if the gas hose pipe is too long.

The double check detector assembly (DCDA) protects the potable water supply line from possible contamination or pollution from: