I find it odd that no one has suggested that the washer in question is functioning exactly as washers have functioned for many, many years. When I was a kid (long ago), virtually all washers in our midwest community had a laundry tub sitting beside the washer with a snorkel shaped drain hose from the washer hanging in it. When you wanted to save the rinse water and use it to wash the next load, you put a standpipe in the drain that would acuse the rinse water to stay in the tub. Then when you washed the next load, the pump sucked it back into the washer and additionally filled until the full sensor stopped it. I believe my mother used it regularly and always washed the 'cleanest' clothes first and the dirtiest last. She probably only used a little over half as much water as she would have otherwise. Maybe some of the areas that are experiencing or going to experience severe water shortages should be investigating renewed usage of these 'suds savers'.
Those anti siphon valves would all have been worthless in this application, because the water would have been pouring into the tub and running down the drain. In installations where the washer does not spray into a tub, but rather discharges into a pipe, the very simple and effective method of preventing backflow is to not seal the gap between the hose and the pipe, so that there is no vacuum created by the falling column of water.
Our city also demands the installation of those anti backflow valves on any faucet that could have a hose attached, which is a totally hysterical response to a very rare problem that is trivial to elimainate. Instead we have valves that spew water out whenever the hose flow is decresed or shut off. The result is that most people remove the valves when they move into a house and only reinstall them when they move out. So the intent of the mandate is defeated, which is OK, because the problem is not real, at least in this city.
Those anti siphon valves would all have been worthless in this application, because the water would have been pouring into the tub and running down the drain. In installations where the washer does not spray into a tub, but rather discharges into a pipe, the very simple and effective method of preventing backflow is to not seal the gap between the hose and the pipe, so that there is no vacuum created by the falling column of water.
Our city also demands the installation of those anti backflow valves on any faucet that could have a hose attached, which is a totally hysterical response to a very rare problem that is trivial to elimainate. Instead we have valves that spew water out whenever the hose flow is decresed or shut off. The result is that most people remove the valves when they move into a house and only reinstall them when they move out. So the intent of the mandate is defeated, which is OK, because the problem is not real, at least in this city.
If there is no water backed up in the sewer pipe your washer drain will work fine. But if you have standing water in the pipe--as was the situation with the sink--water can get sucked back into the washer. An antisiphon unit blocks water flow back into the washer and bleeds in air instead. As one comment noted, many communities require this type of antisiphon, or backflow preventer. We have them on outside faucets and on our in-ground irrigation system. Our town requires annual testing of the backflow preventer on the irrigation line. We don't want water from yards (insecticides, fertilizers, weed killers, etc.) siphoning back into our cullinary-water supply.
I guess I am not sophisticated enough to see this problem. Every washer I have ever connected went into the sewer line. They go up to a pipe, which is attached to a wall and then through an elbow to the sewer. Seems simple enough and I do not have any idea how that sewer water can get back to my washer.
In many urban (& suburban) Plumbing Code jurisdictions throughout this "fruited plain", there are specific requirements that when a clothes washer or a basement bathroom effluent is directed upward to a soil line, there MUST be a check valve in the line to prevent precisely this occurrence. Even lawn sprinkler systems which are connected to a "city" water supply MUST have anti-siphon valves in line w/ the supply line.
My washer, in the basement, pumps the drain water up to a standpipe connected to the large drain leading to the septic system. Occasionally, if the septic tank (more likely the pipe leading to it, as the tank had been recently pumped) backed up, the washer drain hose would syphon the contents of the sewer pipe into the washer when the washer stopped. Yuck! What a mess to clean up and sanitize! I suspect that the problem is roots in the sewer pipe, but can't get at them at present. So, I made up a check valve assembly using PVC plumbing components; this was tightly sealed to the top of the standpipe. Now, the washer pump injects the water into the sewer pipe, but backflow is eliminated. Needless to say, I check the washer tub before starting a new load, in case of a check valve failure.
The anti siphon kit would have been worthwhile if I had anticipated that as being the problem. I decided to examine the functioning first, before getting into what I anticipated that the fault would be, because moving and opening a washer is a dirty job. In this installation the siphon was due to an extension added to the drain hose to reduce the spatter of water out of tyhe washtub.
I did see an installation of a washer in which the drain hose was run straight down to a drain in the basement. IN that setup the problem was quickly obvious in that the washer would never stop filling, and yet never fill. An anti-siphone "tee" at the upper end solved the problem for that installation.
Probably the newer front load washers will have a different set of failure modes.
In the early '70s, at least one manufacturer offered a syphon break kit which was acted much like this fix. It was used when the vent groove that was molded into the end of the rubber drain hose was blocked or when the drain was 'hard connected' without the vent. In addition to allowing air into the drain line to break a syphon, it also prevented the pump from sucking water back into washer.
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