When you install an irrigation system, it’s vital that you also connect it to a backflow prevention assembly. The City of Austin and other Texas municipalities strictly regulate the installation, maintenance and testing of these devices to maintain the safety of the drinking water.
A backflow prevention assembly (BPA) prevents the potable (drinking) water in the public water supply from becoming contaminated if there’s a backflow of non-potable water from your sprinkler system. The BPA is usually installed at a cross connection, which is the piping between the potable water line and the irrigation system (a cross connection is any physical connection between a possible source of contamination and any piping to a drinking water system).
What is Backflow?
Backflow is the flow of water through a cross connection from a possible source of contamination back into the drinking water system. There are two types of backflow: backpressure and back-siphonage.
Backpressure occurs when downstream pressure exceeds the upstream supply pressure in the drinking or public water system due to a high-pressure source. This could be caused by a pump installed on the sprinkler system.
Back-siphonage occurs when there’s negative pressure in the consumer’s potable water system or the public water supply. The negative pressure causes a siphon, similar to drinking from a straw, which allows the flow to reverse to the lower pressure. This can result from different situations, such as repairs to potable water piping, water main breaks, or open fire hydrants.
Irrigation System Hazards
Types of hazards posed by an irrigation system to a potable water supply include:
- Herbicides, fertilizers, pesticides, and animal waste from around the sprinkler heads.
- Pathogens, parasites, insect larvae living in the irrigation system’s water.
- Chemical additives to the irrigation system.
- Connection to alternative water sources such as private wells and rainwater harvesting systems.
Regulations for BPAs
The Texas Commission on Environmental Quality (TCEQ) requires all public water systems to maintain a Cross Connection Control Program to protect the distribution system delivering drinking water, as laid out in Title 30, Chapter 290, Subchapter D, Rules and Regulations for Public Water Suppliers.
Austin Water Utility administers its own Cross Connection Control/Water Protection Program based on TCEQ rules, and in conjunction with their own city ordinances, Chapter 15-1. In Austin, you must have a backflow prevention assembly if your irrigation system is connected to a public or private drinking water supply, and it must be tested upon installation and then annually by a licensed tester (30 Texas Administrative Code 290.44 (h)(4)). Austin’s adopted Uniform Plumbing Code and its local amendments also ensure the proper use of BPAs, and can be found in Chapter 25-12, Article 6.
Types of Backflow Prevention Assemblies
There are many types of BPAs, each designed to provide a different level of protection. Here are the most common ones:
Double Check Valve Assembly (DCVA)
A double check valve assembly consists of two independently acting spring-loaded check valves. There are shutoff valves at each end, and it has four test cocks. It can be installed either above ground or inline (below-grade or underground and parallel with the system’s piping), as well as indoors.
Installation requirements above ground:
- Horizontal (preferred) or vertical, with the flow upward.
- Minimum of 12 inches to a maximum of 60 inches clearance between the finished grade or floor and bottom of the assembly.
- Service side of assembly requires minimum of 24 inches unobstructed clearance for testing, repairs, and replacement.
If the DCVA installation is in a pit or vault, make sure there’s proper drainage so it doesn’t become submerged.
Installation requirements below grade:
- Test cocks must be plugged, except when the double check valve is being tested.
- Test cock plugs must be threaded, water-tight, and made of nonferrous material.
- Test cocks to discharge vertically upward.
- A y-type strainer installed on the inlet side.
- Clearance between any fill material and the bottom of the double check valve to allow space for testing and repair.
- Space on the side of the double check valve for testing and repairs.
A DCVA is effective against backpressure backflow and back-siphonage but should only be used to isolate non-health hazards. Do not use a DCVA with chemigation.
Reduced Principle Backflow Assembly (RPBA)
The reduced principle backflow assembly is also known as a reduced pressure zone assembly (RPZ), reduced pressure backflow assembly, and reduced pressure principle assembly. It contains two independently acting spring-loaded check valves with a hydraulically operating, mechanically independent, spring-loaded pressure differential relief valve located between the two check valves and below the first check valve. There are shutoff valves at each end of the RPBA, and it also has four test cocks.
The most complex and expensive backflow assembly, it is also the most effective against backpressure backflow and back-siphonage. It may be used to isolate health or non-health hazards. You should install an RPBA if:
- There’s a well on your property or any other auxiliary water source such as cisterns or rainwater harvesting systems that could potentially be cross connected and contaminate the city water supply.
- You’re using any type of water or pressure pump that could potentially force contaminated water back into the city water supply.
- You have any fertilizer/chemical injection system connected to the irrigation.
An RPBA will periodically discharge small amounts of water due to fluctuation in line pressure upstream or downstream to it. Install it in areas that won’t suffer water damage and be sure to provide adequate drainage.
- 12 inches minimum to a maximum of 60 inches clearance between the finished grade or floor, and the bottom of the assembly.
- 12 inches minimum clearance above, and 24 inches minimum unobstructed clearance on the service side of the assembly.
Pressure Vacuum Breaker Assembly (PVB)
There are two styles of PVBs: the pressure vacuum breaker, and a spill-resistant vacuum breaker (SVB). A PVB occasionally discharges water, so install the spill-resistant model for indoor use if spillage would be a problem. You will also need an air gap drain if the assembly is installed in a basement or other interior area.
The PVB is the most common, inexpensive type of BPA for a whole irrigation system. Their design is relatively simple, and they’re easy to install, maintain, and repair. The assembly consists of an independently acting, spring-loaded check valve, and an independently acting, spring-loaded air inlet valve on the discharge side of the check valve. Each end of the PVB has shutoff valves, and there are two test cocks.
- At least 12 inches above the highest downstream point on the system (usually the highest sprinkler head), with enough clearance for testing and maintenance.
- Vertical installation, with the inlet at the bottom.
PVBs are effective against back-siphonage only and may be used to isolate health or non-health hazards. You can’t use chemigation (the application of fertilizer, herbicides, insecticides, fungicides and other chemicals through irrigation systems) with PVBs.
An air gap is simply a vertical, unobstructed physical separation between the end of a water supply outlet and the flood-level rim of the receiving receptacle. The separation must be at least twice the supply pipe diameter, but never less than 1.0 inch.
Air gaps protect against both backpressure backflow and back-siphonage. They may be used to isolate health or non-health hazards but they aren’t always practical. The supply pressure is lost, and the receptacle and water are exposed to the surrounding air with its pollutants, pathogens, and debris, and thus may no longer be potable.
Smart Earth Sprinklers specializes in the installation, testing, and repair of backflow prevention devices. Call us at (512) 694-1147 or contact us online today.