Yet again, our Sherlock Ohms notices something out of the corner of the eye that reveals the problem is not what it initially seems. Sherlock Ohms assumes nothing. Sherlock was called in to fix a washer, but when the water is not draining well, the problem may be with the drain path and not the washer.
The symptoms here sound a lot like those in an earlier Sherlock, where the culprit turned out to be a water fill level sensor for the rinse cycle, if I remember right. That earlier Sherlock had the same solution as our own washer's fill problem after rinsing. I admire the determination to find the solution in both of these, since the symptoms are apparently identical. It sure took us a few tries to find the right answer.
Maybe it's time for Maytag or Whirlpool (or other appliance manufacturer) to pen an article for Design News. Give them an opportunity for rebuttal, however I'd ask you to lay down firm ground rules. They'll be writing to engineers and designers; simple (dumb) sales propaganda will not be tolerated. If they can avoid that, you might find some interesting discussions result.
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.
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.
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.
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.
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.
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.
For industrial control applications, or even a simple assembly line, that machine can go almost 24/7 without a break. But what happens when the task is a little more complex? That’s where the “smart” machine would come in. The smart machine is one that has some simple (or complex in some cases) processing capability to be able to adapt to changing conditions. Such machines are suited for a host of applications, including automotive, aerospace, defense, medical, computers and electronics, telecommunications, consumer goods, and so on. This discussion will examine what’s possible with smart machines, and what tradeoffs need to be made to implement such a solution.