Ever see those big valves sticking out of the ground near the sidewalk and wonder what they are for? Have you heard of anti-siphon devices and wondered what they were talking about? Even though you may not know what they are they work relentlessly to protect the public health. These valves are installed on domestic water lines to prevent the back flowing of water into your fresh water supply.
Now, you may ask, when is it possible for water to flow backwards into the fresh waterline? Often, when there is a fire, firetrucks will pump the water from the domestic supply. If, during this time you are say, filling a swimming pool, the negative pressure will siphon the water from the pool and make its way back into the utilities water supply contaminating it. Same goes for when you are gardening and lay the hose on the ground and the water is drawn back into the water supply dirt and bacteria can contaminate the water supply.
Back flow devices and anti-siphoning devices prevent this from happening. With back flow devices if a negative flow occurs the valve "checks" or prevents the flow of water when the pressure coming into your supply is lower than the pressure already past the valve thus preventing an equalizing or back flow situation. This is usually accompanied by what is commonly called dumping. This occurs when the water is released from the relief valve it is a sign that a back flowing has attempted to occur.
Anti-siphon devices are somewhat the same although they usually are installed on landscaping supply lines and hose bibs. These prevent back flow by opening and allowing air to enter the line when a negative pressure situation occurs.
If you have any questions or comments about installing or maintaing your backflow devices feel free to call me at (408) 263-8433.
your plumber,
Cameron
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