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What is a Backflow Preventer and How Does it Work?

Van Nuys Leak Detection & Mold Remediation

What is a Backflow Preventer and How Does it Work?

What is a Backflow Preventer and How Does it Work?

Jim: Hello, this is Jim here with the Twin Home Experts. We’re here with our backflow tester, Henry. Henry, can you explain what a backflow does?

Henry: Well, a backflow preventer essentially protects our drinking supply water. You’ve got domestic water supply here, from the meter to the backflow preventer. Once it goes through the backflow preventer, the city’s concern is that it doesn’t re-enter back into the main supply. So, in this particular case, this is a meter service protection valve. As the water goes through it, there’s a check here, a check here, and a relief valve that’s located in between. It’s all hydraulic.

The relief valve’s located between the two checks. The relief valve will actually stay closed by high pressure. That’s keeping the relief valve closed. The check valves are normally closed, until there’s flow going through the device. Now, if there’s an issue with the valve, if you’ve got a leaky number two check, with back pressure on the system, the relief valve will actually open and dump. If you’ve got a problem with the number one check valve, unless there’s a problem with the relief valve, the relief valve should be opening to the atmosphere. What that does is it actually releases that water and brings in air to break any vacuum between the two.

Jim: Now, let me ask you, Henry, every property owner gets a notice once a year?

Henry: Once a year, right.

Jim: Why is that important? Why does the city want to know?

Henry: Well, the city has to actually maintain a record of all backflow preventers. It’s actually a statewide law. This is something that has to be done once a year, and the only way that they can do that is by a paper trail, having someone that’s certified come out and actually perform a test on the valve. Once they perform the test on the valve, we have requirements that we have to fill out paperwork, and mail that paperwork in either to the county, it would be L.A. County Health Department. It could be Ventura County Health Department. It could be the City of Los Angeles Water and Power, or whoever your meter person is. It could be any water purveyor.

Jim: Awesome. Henry, thanks for taking the time.

Henry: Okay, buddy.

Jim: Let’s get to it. Thank you.


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