Anti Siphon Valve vs Backflow Preventer

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When it comes to keeping personal water supplies safe from a possibly contaminated reverse flow, you have to decide between an anti siphon valve or a backflow preventer.

This comprehensive anti siphon valve vs backflow preventer comparison guide will help you make an informed decision for your home’s plumbing.

Read to the end.

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Anti siphon valve vs backflow preventer – how does each device work

To determine which is best to use for your water supply, it’s important to understand how both components work.

First, let’s define the two devices for the benefit of those hearing about them for the first time.

What is a backflow preventer?

To begin with, you need to understand that backflow preventer is a term used to represent a whole family of products used to arrest the unwanted flow of liquids backward (in the alternate direction). 

It, therefore, follows that a basic anti-siphon valve is generally considered a backflow preventer!

However, there has been much advancement over the years and specialized backflow preventers today dominate and are, in fact, the preferred choice among plumbing professionals.

This anti siphon valve vs backflow preventer article assumes that you have the dedicated backflow preventer in mind.

Of course, it gives you more peace of mind since you’re sure that not a single drop of polluted water will find its way into your house’s ‘main’ water supply via a backflow incident.

What is an anti siphon valve?

An anti-siphon valve is simply a one-way valve that allows water flow in just one direction.

There are several anti-siphon valve models with most using similar controls to prevent water – which is potentially overflowing with contaminants- from flowing back into the potable (drinkable) water source.

How a backflow preventer works

The devoted backflow preventer is a pretty sophisticated appliance with numerous valves, air vents, testing systems, etc. (visualize a human heart!) to help it function as wanted.

But how exactly does it operate?

Now, a backflow preventer operational principle is rather basic- water enters through one way and it shuts when building pressure tries to force the liquid back through.

For clarity purposes, I must mention that backpressure conditions arise when higher pressures -than within the supply- occur in the downstream pipes, causing the highly pressurized downstream water to flow into the water source.

Sure, there are slight variations- depending on the specific backflow prevention device/assembly you have- but, by and large, this is the simple technique used by preventers to keep water carrying toxins (from the yard sprinkler system and elsewhere) off your water supply.

To offer maximum protection, backflow preventers are installed at cross connections (points where potable water systems join non-potable water systems) in the plumbing as there is more risk of poisoned fluids entering the pipes supplying drinking water here.

How an anti siphon valve works

To get the hang of how these types of valves function, think of a fuel tank installed above a gas station.

Naturally, fuel will constantly be flowing through the piping going to the dispensing pump (stands at a lower position) thanks to the gravitational force.

Logically, you don’t want this to be happening – except when you specifically desire – making some type of shut off mechanism essential to the installation.

An easy way of achieving this goal is to have an anti siphon valve added in a strategic location such as the tank’s discharge piping.

Generally speaking, anti-siphon valves – they can be manual or automatic (with built-in atmospheric vacuum breakers) – play almost the same role when deployed in water systems.

Anti siphon valve vs backflow preventer – when to use each 

Once mounted, both devices stop toxic water from the pipes from getting into clean water supply systems when pressure decreases or is completely lost.

They’re essentially critical components and building codes require that you include backward flow protection in all susceptible places around the home.

That said, there are situations each will deliver best, and knowing them will help you arrive at a decision you won’t regret down the road. 

1. The best applications for Anti siphon valve

On the whole, an anti siphon valve is the most sensible preventer for deployment on your residential irrigation system for the simple reason that it’s simple to implement and quite inexpensive.

But don’t rejoice yet- there are jurisdictions that have outlawed anti-siphon valves (because they don’t stand up to extreme backward pressure that well) and we suggest that you confirm from your local municipality before proceeding.

Two things come to mind if this option is acceptable in your case…..

First, you must purchase the right model of anti siphon valve (some of the cheaper brands tend to disappoint).

Secondly, you must get the installation right- they’re most always installed at the highest position in the garden you’re irrigating and at least 6”above the surface.

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2. The best applications for backflow preventers

On the other hand, a backflow preventer tends to provide an indomitable line of defense for backflow problems in the following circumstances:

  • Commercial projects– for apartments, condominiums, and fundamentally, all business properties, a backflow preventer is the industry standard.
  • Irrigation systems in which you plan to be feeding fertilizer, insecticides, and other products – all these substances can be lethal and you don’t want to take chances.
  • Where it’s impossible to install anti siphon valves properly –recall the requirement that they are above ground.

Anti siphon valve vs backflow preventer- take away

Your first line of defense when it comes to protecting potable water sources from contamination is either anti siphon valves or a suitable backflow preventer.

As such, here is what you should carry with you as you walk away:

Overall, because of economic reasons and simplicity of application, an anti-siphon valve is the weapon of choice for residential irrigation systems.

In contrast, many people use backflow preventers (remember there are several excellent types) on commercial properties, irrigation systems used for feeding products such as fertilizers to crops, and where it’s impractical to mount anti-siphon valves.

One last thing: the building codes in your area have specific provisions and you’re bound by them so check the local regulatory requirements before making a final decision.

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