The very first step to take is to determine which code is the correct one to comply with. A backflow prevention assembly can be installed as a service protection assembly or an internal protection assembly. A service protection assembly is installed at the point of service to a water user; this type of assembly is installed to protect the distribution system from a backflow event. These assemblies come under the control of the State Administrative Code. Each state administrative code has restrictions as to what and where some assemblies can be installed. If the installation is an internal protection assembly, the local adopted Plumbing Code will usually govern the installation. Internal protection assemblies are installed to protect the quality of the drinking water within the water user's building by protecting a specific piece of water-using equipment.
Consider whether this is a brand new installation into a new or existing piping system that is currently without a backflow preventer, or, is it a replacement of an existing assembly already installed? The replacement of a previously installed assembly may still require you to meet existing code. Just because a DC type assembly may have been installed in the past, does not necessarily mean you can assume a DC is the proper type of protection today. When changing out an old assembly that cannot be repaired, first be sure the new assembly meets existing code.
Secondly, The degree of hazard for which the assembly is being installed must also be determined. The degree of hazard can be a health (high) or non-health (low) hazard. High hazard assemblies are the Reduced Pressure Principle Assemblies (RP) and the various types of Vacuum Breakers, Pressure, Spill Resistant or Atmospheric (PVB, SVB, and AVB). The low hazard assemblies are the double check type (DC).
Next, evaluate the type of backflow you are trying to protect against, either backpressure and/or backsiphonage. The RP & DC can be installed to protect against backpressure or backsiphonage. The various types of Vacuum Breakers can only be used to protect against backsiphonage.
Once the code, degree of hazard, and type of backflow is determined, you can look to your list of approved assemblies. The list of approved assemblies is usually established by the administrative authority that has jurisdiction. The different types of backflow prevention assemblies have restrictions as to how they can be used. It is important that they only be used in the same installation orientation and type of protection as determined by the approval agency.
The most recognized approval agency is the USC Foundation for Cross Connection Control & Hydraulic Research. Manufacturers submit their assemblies to the Foundation for approval, which must then go through a lab approval and field approval process. ; Not all assemblies pass the approval process. If an assembly passes approval, it is included in the Foundation's list of approved assemblies. The list indicates, for each assembly, the approved model, size and orientation. .
Once you have all these facts, you are ready to evaluate the considerations of the installation process: the hydraulic conditions, and the mechanical conditions. The hydraulic conditions have to do with the flow of water through the piping system. The mechanical conditions have to do with the pipe, valves and fittings needed to properly install the backflow preventer into a piping system.
The hydraulic considerations of installing a backflow preventer must include sizing, pressure and temperature. In most installations, the size of the piping and the backflow preventer has already been determined by an engineer who evaluated the fixture use of a piping system. If there has not been a hydraulic review of an existing or newly designed piping system, be sure the changes to flow and pressure by the installation of a backflow preventer are evaluated before it is installed. Installing a backflow preventer into an existing piping system can change the workings of some piping arrangements such as irrigation or fire systems.
Some piping systems will require continuous water supply due to their water needs. Applications such as supply services to hospitals are considered critical services where water cannot be discontinued even for short periods of time. This type of critical service will require the installation of parallel backflow preventers to ensure that when one backflow preventer is shut off for servicing, the other preventer will allow water to flow to the piping system. When installing parallel installations, be sure the separate and combined flows of the backflow preventers meet the needs of the water user.
In some cases, piping systems may be improperly sized and subjected to sharp changes in pressure due to excessive demand or flows of water within a piping system. This sudden change to supply pressure of assemblies, such as RP's, can lead to an intermittent discharge from the relief valve. The piping system must be evaluated to determine why the pressure fluctuations are occurring, and to see if the pressure fluctuations can be minimized. A resilient seated check valve at the inlet of the RP may help minimize the effect of pressure fluctuations and minimize any unwanted relief valve discharge.
The pressure that is consumed by an assembly can be calculated by looking to the flow chart for that assembly. Be sure you are observing the flow chart for the correct installation orientation; a flow chart for a horizontal orientation could differ from that of the vertical orientation. Also be sure, when evaluating the pressure loss on a flow chart, that you evaluate the pressure loss at different flow rates. The loss of pressure through a backflow preventer is not the same at all flow rates.
The other consideration is the incoming supply pressure in the piping system. The maximum working water pressure (MWWP) for an assembly is established by the manufacturer and confirmed in the approval process. The assembly should never be subjected to a pressure that exceeds its MWWP. Exceeding this pressure can void any warranties and also may render the backflow preventer inoperative. The excessive pressures present in a piping system can exert an undue stress on the preventer or piping system. If the supply pressure is above the assemblies MWWP, a pressure regulator must be installed. Most plumbing codes do not allow excess pressure without the installation of a pressure regulator. The supply pressure from the Water Purveyor to a water user's piping system is not always constant. Inlet pressure can fluctuate due to conditions such as: level of demand upstream of the point of service, or pumping schedules within the water system. Be sure to evaluate the incoming pressure at different times of the day to assure the actual incoming pressure you will be dealing with. On the upstream side of the assembly, the MWWP must not be exceeded for any reason and the code required minimum pressure must always be delivered to the farthest remote fixture regardless of the equipment it must pass through.
Even if proper pressure parameters are achieved on the upstream side, the downstream side must also be evaluated. When a backflow prevention assembly is installed, a closed system is established on the downstream side. These means any built up pressure in the piping past the backflow preventer is locked into the piping system and cannot escape past a working assembly. Even if the normal incoming line pressure is below the MWWP, excessive pressure can easily be created downstream by pumps, thermal expansion, boilers and other conditions and equipment that can quickly create excess pressure beyond the MWWP on the downstream side. The use of quick closing valves such as electronic solenoids or ball valves can create a water hammer, which can lead to excess pressure being trapped on the downstream side unless some type of pressure and or temperature relief device or expansion tank is utilized. Proper pressure parameters must be evaluated on the upstream and downstream side of the assembly. Normal and abnormal pressure events must be evaluated to assure it does not adversely affect the installed assembly.
The working temperature range of a backflow preventer is established by the manufacturer. The approval agency will confirm the temperature range at which a backflow preventer can function. The application of excessive temperature can cause the backflow preventer to not work properly. Too high of a temperature can affect the strength of some plastics and rubbers. Too low of a temperature can also cause the backflow preventer to become inoperative. The temperature evaluation must be made not only for the fluid temperature, but also the ambient temperature around the installation site, which can change fluid temperature.
Any mechanical equipment can be fouled if water entering the backflow preventer is not free of particulate. When properties other than clean water flow through a backflow preventer, these pieces could lodge into a critical sealing area. To collect these particles, the installation of strainers may help to remove the particles from affecting the backflow preventer. A strainer cannot be installed in any piping arrangement without proper evaluation of rules and hydraulics.
If a backflow preventer is installed for service protection, many cross connection control program rules do not allow the installation of any connection before a backflow preventer. A strainer usually has a blow off hole to remove the accumulated particles from the piping system. In some cases, this blow off hole is improperly used as a connection to piping fixtures before the assembly, such as irrigation connections or hose bibs. If a strainer is needed before a service protection assembly, be sure to consult with your local administrative authority before proceeding.
Strainers can usually be installed in front of internal protection backflow preventers. Strainers will affect the flow of water into a piping system. A strainer contains screens, which will restrict the volume of water that can flow past it. Strainers cannot be installed where this reduction in effective area leads to a restriction that prohibits the working of the piping system; for example, in installations such as fire or irrigation systems. When strainers must be installed, be sure the piping system will still work properly. Regardless of where the strainer is installed, it must be periodically serviced by cleaning the screen and removing any accumulated particles.
Once we get past the problems of hydraulics, we must look to the mechanical concerns of installing a backflow preventer. The first concern to evaluate is the installation orientation. Backflow preventers must be installed in the installation orientation for which they were designed and approved (vertical, horizontal etc.). There are backflow preventers that can be installed horizontally, vertically (up or down) and other orientations that can make an installation easier. The key point to realize however is that they can only be installed in the orientation that the approval agency has determined they will work in. Some manufacturers may state that it is acceptable to them to install in other orientations, but you need to be sure it is listed on your list of approved assemblies in that orientation.
When installing any backflow preventer, it is important that it be installed into the piping system properly. The type of pipe and piping connections used are established in various piping codes for your specific area, and must be followed. The proper installation of braces, brackets, mounting pads or supports assures that the installed backflow preventers will continue to work properly. It is important that all pipe, valve and fittings are of the correct material and installed as required. The weight of the assemblies, the attached piping, and the force of moving water are all substantial concerns, and must be properly evaluated. Even the forces needed to take assemblies apart for servicing could cause problems if the piping is not securely installed.
Another key concern is accessibility to the assembly once it is installed. All backflow preventers require some type of regular inspection and servicing. To assure this inspection and service is done properly, an adequate work space must be left around the backflow preventer. This space will vary depending on the type and size of backflow preventer that is installed. The installation of the backflow preventer must be in a location where access is not restricted by piping, walls or any other restriction.
The installations of assemblies in areas where the entry or exit are restricted are considered confined spaces. Installing assemblies in areas that are classified as confined spaces requires specific entry and exit protocols by the technician to ensure that there is no danger entering into the confined space, such as lack of oxygen or accumulation of dangerous gases. Since backflow preventers must be periodically serviced, it is important that the backflow preventer be installed where it is easy and safe to get at or around it for maintenance or testing.
The height at which the assembly is installed in relation to the surrounding grade is also important. Some assemblies, such as RP's, have key minimum height requirements to ensure that the relief valve will not be submerged or engulfed. PVB's must be installed at a minimum of 12" above the highest point of use and any downstream piping to assure it works correctly. Most Plumbing Codes also establish maximum height requirements. These are done to assure maintenance is properly performed. Most codes state if installation heights greater than 5 feet above grade must be used, a permanent work platform must be built around the assembly for servicing.
Installing assemblies that can discharge water (RP, RPDA, PVB, SVB) can lead to another set of concerns. Water that can discharge from assemblies does not usually cause any concern when installed outside; however, when assemblies are installed inside buildings, the discharge is usually piped away to a drain. This drain piping must be properly installed so a cross connection is not created between the drain and the assembly discharge. Most manufacturers of RP's also produce an air gap drain attachment that assures that the proper separation is achieved from the relief valve discharge and the drain line. An air gap drain is designed to carry away an occasional dripping or mild discharge only. The full discharge of the RP is well beyond the capacity of the air gap drain attachment.
A backflow preventer may be required to be installed outside of a building where the weather environment can affect the backflow preventer. Enclosures may need to be installed around a backflow preventer to assure the backflow preventer's temperature parameters are maintained. Enclosures can also be installed for vandal control to restrict who can operate the piping system. Enclosures can also be placed around assemblies for aesthetic reasons to minimize their intrusion into a landscape.
Backflow preventers are installed to protect against an identified hazard be it high or low. Use the following checklist to properly and successfully install a backflow preventer: