One recent morning, I opened my dishwasher expecting to find clean, dry dishes, but instead I saw that the water had not drained.
I removed the top panel to expose the control panel and dishwasher controller. The dishwasher cycles were driven by a timer mechanism with contacts that opened and closed as the timer rotated.
Behind the panel, I also located a full working electrical diagram on which I located the drain pump and the signal wires that drove the pump. On the exact set of contacts that controlled the drain motor, I found the remnants of some type of water bug that had made its way into the timer and decided to reside in the contacts. I decided this unfortunate creature had shorted out the contact with another contact and shorted the motor.
After cleaning the contacts, I emptied the washer basin and pulled out the unit. The drain pump was easy to access, and I pulled off the pump and hooked it up to an auxiliary 120V power source, which still did not turn the pump, so I bought a new pump and installed it. The pump worked, and I reinstalled the unit.
The problem was solved until three days later, when the water again did not drain. I checked the contacts, and there were no bugs, so I pulled the unit and pump out again. This replacement had a removable casing covering the impeller blades. I removed the casing and found a piece of glass that was blocking the blades from turning.
I removed the glass, and the blade moved freely. I also checked the original and found another piece of glass. I then checked the trap on the bottom of the washer and found additional pieces of glass that had passed through the debris filter. I removed these pieces and re-installed the original pump.
It has worked great since this last repair. Evidently, a glass had broken during the wash cycle at some point, and the broken pieces had worked their way through the system, jamming the pump. This was one situation where an obvious problem was not the actual problem.
This entry was submitted by Tim McNulty and edited by Rob Spiegel.
Tim McNulty is an engineering graduate of Penn State University. He works as an engineer in the plastics manufacturing industry specializing in injection molding.
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.
Kudos to you for continuing to search for the culprit. I have to admit while I haven't experienced the bug problem, we've definitely run into similar issues with glass and other elements being trapped in places that block water flow and essentially wreck havoc on the dish washing cycle. Given that I hardly expect we're alone in this probem, it seems to me, a bit more engineering time could be spent on coming up with a better design for dealing with debris so it doesn't interfere with the unit's operation.
I had a pistachio shell that made its way to the pump. The noise it was making suggested a bearing had gone bad and that a new pump was in my future. I'm glad I decided to open the machine up and take a look before ordering a pump. That made me wonder about the people that don't own screwdrivers and what they would do. Call repair service and buy a new pump? We're all lucky to be engineers.
While I agree with you, (lucky to be engineers) I've been forced in many instances to rise to a higher, broader perspective, and know firsthand that the general public (family members included) don't always share that perspective.A colleague of mine has a book on his desk entitled Design Engineering, and depicted on the cover is a bridge spanning a great chasm; one side of the bridge says "Design Engineers" and on the opposite reads "The Rest of the World".Yes, we are set apart, and by our perspectives, happily so; but many times from the perspective of the "The Rest of the World" it's their choice to isolate us.Everything is relative. But that's just an engineer's opinion.
Oh, and about the dishwasher – funny story;too bad the insect wasn't the real bug; that would have been poetic!
How long before the pump stopped working was the broken glass discovered ? Did that person not look for all of the pieces ? And how small was the piece that blocked the impeller ?
Both pieces of glass were about 3 x 3 mm which was just a little too large to allow the impeller to turn. The broken glass was about 2 weeks before we had the issue with the drain.
This story makes me wonder about the filters: why aren't they designed to prevent small items like pistachio shells and broken glass shards from entering the pump, or for that matter, from ever leaving the dish compartment in the first place?
Good question, Ann. My dishwasher is designed so nothing larger than a sunflower seed can get through the main compartment. It's not a fancy filter, it's just that the holes for water passage are very small. Seems an easy and logical design.
It seems easy and logical to me, too, Rob, although experience tells me that's not good enough when it comes to the realities of machines. But a sunflower seed may be large enough to do damage, since others mentioned a pistachio shell and glass fragments. So I'm wondering if a filter small enough to keep out these objects might also be too fine to let water pass through at high enough rates, or that maybe there's another design problem such a fine screen would cause.
Good points, Ann. There may be a potential problem if the filter was so fine that it would quickly get clogged. So there is probably a design balance between having it fine enough to catch items like glass while still allowing a flush that doesn't quickly clog.
Rob, that's what I figured: there must be a (very imperfect) balance in designing these between filter hole size small enough to prevent damaging particles from passing through and filter hole size large enough to keep water flowing at the right rate of speed. Tim's dimensions are a lot smaller than a sunflower seed and larger than a size that I'd guess could cause a clog.
That's right, Ann. It seems a simple matter. So I'm surprised there are designs that make it so difficult for users. The fascinating part of this story, though, really is the bug getting into the control panel. How do you design to avoid that?
Mine has a filter screen as well, but all kinds of "crap" gets through anyhow. The most annoying are little pieces of plastic film that go through and clog the exit holes of the top/bottom rotating sprayers. Can't complain though - its going on 14-15 years and still does the job as long as it gets a routine clean-out.
Yes, I'm in the same boat, Droid. I have to clean the filter holes, but is is at least visible when I open the dishwasher door. I don't have to take anything apart to find the trapped gook.
Our $400 late-model Frigidaire dishwasher has a strainer in the bottom to capture larger debris, to prevent the larger debris from entering the pump. It's a regular maintenance item to clean-out the strainer (preventative maintenance if done on a regular basis, corrective maintenance if deferred until clogged). My wife cleans-out the strainer about once a year, easily accessible and easy to clean. The dishwasher user's manual explains and illustrates how to clean the strainer. We're also careful to rinse all excess food before loading items into the dishwasher.
Looking at the filter and setup, I still do not necessarily know how the glass got to the drain motor. There is a top filter with multiple small holes and a locking ring that holds this in place. The best I can figure is that somehow the edge of the filter was pushed up during the cycle and the glass worked its way in.
My experience with broken glass in a standard (builder's grade) dishwasher is that large enough pieces of glass can get in and destroy the pump, shearing off most of the vanes on the plastic impeller!
Found the glass, found most of the impeller blades, never did figure out how the glass got through the screens to the pump.
We had a dishwasher that seemed to chip plates and no one could figure out why. Turns out we found bits of broken galss lodged in the sprayer, and smaller bits were apparently circulating through the spray nozzles at high exit velocities. It took a careful cleanout to remedy the problem.
At least your dishes should be super clean as they were being sand blasted as well as washed. The each little chip probably became part of the blasting process. I wonder just how far it would have gone before blowing a hole through the door. Just a thought.
Interesting to read about a real bug in a circuit, but perhaps the problem was the bad pump and the insect didn't have any effect. Who knows; it's a good story.
Grace Hopper, a US Navy admiral, worked on many early computers and taped a moth in one of her lab notebooks. The story goes she found the moth between relay contacts in a Mark II computer, noted the problem, and told people she was "debugging" the circuits. Find more info and a photo of the mounted bug here: http://en.wikipedia.org/wiki/Grace_Hopper.
While inspecting circuit boards a friend of mine spotted an insect on the reverse side of a board. He turned the board over, but no bug. It was sandwiched between the fiberglass sheets used to create the substrate. I think I have a 35-mm slide of the encapsulated bugaround here somewhere. The board was "buggy," but thankfully the creature didn't affect any of the circuits.
Jon, I heard the same story about Grace Hopper inventing the term "debug". A friend of mine who used to work tech support years ago told me that real bugs getting into electronics have in fact been the problem in many cases, at least on the old days with larger components.
Talking about large equipment: You can blame squirrels for many above-ground power failures, Ann. They run along wires and sometimes put their paws on a transforner terminal while standing on the metal case. That causes a brief short circuit that blows a fuse on the power pole. It kills the squirrel, too. I haven't heard about any squirrels in computers or appliances, though.
I hadn't heard about the transformer issue. But I'm familiar with the problems squirrels cause in gnawing wires. The first three times my internet cable connection failed out here in the forest the Comcast tech said it was all their fault. Maybe they've learned, since we haven't had that problem since. My friends in the drier areas where there are many mouse and rat species tell me they continually have car failures caused by mice and rats gnawing electrical wires.
Those little critters seem to gnaw at almost anything that might resemble food. My father in law had a porcupine or raccoon nibble through a brake or power-steering hose. The repairman said most likely there was road-salt on the hose and animals like salt in their diets. Who knew.
An interesting biology tidbit: rodents actually gnaw on all kinds of things that don't look or smell like food. It's to keep their teeth, which continue to grow throughout their lives, at a reasonable length, so they don't grow into their jaws. That's why they are the main wildlife, at least in temperate zones, responsible for destroying so many electrical wires.
Another interesting critter is the ant. When I lived "out in the country", ants swarmed the contactor on my air conditioning unit, rendering it useless. Also got into the telephone junction box outside and disrupted it, too.
I know this is a little off topic, but I heard a story of a grizzly bear getting into a high voltage power line. The story turns out to be true and with a little surfing you can find pictures of a grizzly bear that dug up a high voltage power line. I always wondered if the hum made him think the cable was somehow linked to a bee hive.
Ants seem especially attracted to electric fields. I lived in Plano, TX some years back, and my house there had a low-voltage outdoor lighting system. It was fairly extensive, with a several hundred VA transformer. I had a series of failures, including one that got me a new transformer (in warranty) because of an open winding. It had dual outputs (separate windings), and the other one still worked. It turned out that each winding had an internal overcurrent protection device (besides the primary-side circuit breaker, and non-repairable) that would blow only if there was a major overload that peaked too quickly for the breaker to trip. I had lots of "fun" excavating all of that LV wiring to isolate the wiring fault, that showed up as a 0.1 ohm or so short on one LONG run of 12 AWG LV "burial" cable. I finally got to the problem: a splice (thoroughly taped, and with "lock" type crimp connectors) at a break-out point to split in 2 directions. For some reason, it had attracted a whole mound of FIRE ANTS that chewed away enough insulation to cause the short. Of course, I had to first wipe out the nest, wait for all the ants to die or otherwise depart, then rewire and re-tape that part of the run. All was well for a few months. Then, the same run failed again. Same spot, same reason (only this time it didn't kill the transformer, as the breaker did its job that time). I fixed it again, and the problem recurred a couple more times (that I know of; sold the house and moved back to Atlanta!). I did some checking around, and found that indeed fire ants for no known reason WERE attracted to electric wiring! Apparently, normal line voltage lighting doesn't have the problem; maybe the fields are strong enough that the ants get zapped before they can do much damage!
Ratsky-- good to see your tag again. Can't tell you how many times bug-eaten wire insulation has appeared in the Sherlock Ohms and Made by Monkeys blogs. Seems there should be some off-putting chemical in the insulation to prevent this common problem.
Ratsky, please tell me if I'm remembering this correctly: Wasn't the federal government supposed to build a big particle accelerator in Texas in the 1990s, which ultimately had to be delayed (or cancelled?) due to fire ants being attarcted to the accelerator's huge magnetic fields?
I'm afraid neither I nor Google can remember or find anything about that! Try Snopes; sounds like an (non)urban legend! There may have been other reasons. Most of Texas has relatively unstable soil formations (that's why few newer houses have basements, because the codes now require floating slab foundations).
The Superconducting Super Collider (SSC) (also nicknamed the Desertron[1]) was a particle accelerator complex under construction in the vicinity of Waxahachie, Texas that was set to be world's largest and most energetic, surpassing the current record held by the Large Hadron Collider. Its planned ring circumference was 87.1 kilometres (54.1 mi) with an energy of 20 TeV per proton. The project's director was Roy Schwitters, a physicist at the University of Texas at Austin and Harvard University. Dr. Louis Ianniello served as Associate Director.[2] The project was cancelled in 1993 due to budget problems.[3]
Waxahatchie is about 30 miles due south of Dallas, and certainly would have both fire ants and sandy/shifty soil structure. I suspect part of the "budget problems" was failure to see how expensive solving foundation problems would be! Typical government boondoggle IMHO. Thought so at the time, still do!
I thought that was a huge disappointment when it was cancelled, Ratski. So instead of Texas, Europe gets all the glory, all of the jobs, and all of the resulting technology.
Squirrels seem to love to chew on vinyl. They've gnawed through a heavy vinyl birdseed container. Far worse was when they gnawed the insulation from the low-voltage wiring to my heat pump, causing continuous compressor start-stop cycling. The compressor wasn't designed for that and failed, necessitating replacement of the entire unit, costing a few thousand dollars.
Needless to say, the current unit has the low-voltage wiring run inside steel-jacketed "Greenfield" tubing.
When I was a young teen, we moved into a rented house, where the electric range did not work properly. On pulling the range out from the wall, we found a rat that had been electrocuted and cooked across the terminals where the 240 VAC feed from the wall socket connected inside the range.
I would think the rat would stink and alert the occupants that something was amiss behind the stove. I once used rodent poisen to get rid of mice. They would eat the poisen, then crawl into the walls to die. We could smell them for a week, but we couldn't get to them.
My guess is that it did, until it was thouroughly dessicated by the current passing through it. We had just rented the house, and the cooked rat in the range came with it. Who can account for some people not investigating smells. I have always tried to locate the source of any unusual odors, whether foul or pleasant. In fact, I have often located the failed component on circuit boards by the smell, usually confirmed by either discoloration or deformity caused by the overheating when it failed.
When I used mousetraps it was easy to find the dead mice. But when they crawl into the wall to die after being poisened, it's not so easy. I could always locate the area, but I didn't cut through the wall. So I quit using poisen.
That is interesting information about the origins of de-bugging. I guess that bugs have been around a long time and continue to pester all different ways.
Good comments, John. Kudos for attributing "debug" properly to Grace Hopper.
My company makes electronic equipment for use throughout the world. The gear used particularly in the more tropical climates is often assailed by various and sundry "vermin". It's often a design consideration; water ingress is one thing, but is it vermin-proof? Ha! Maybe the most unusual incident occurred when we brought a pallet of gear into the factory for rework from the field. A lady opened up the housing of one unit to find a 6" long snake! True, it was dessicated and no threat, but still quite shocking (pun intended). Critters always seem to seek out warm hidey-holes.
@jmillion: Yes, like the "warm hidey-holes" in my swimming pool pump motor! The thing is black, of course, sitting in the sun, and close to the ground. It started making an awful racket, so I brought it down to my workshop to see if I could fix it. I hadn't gotten much more than the back cover off when out comes an 8-inch long garter snake! Boy, did I jump! Fortunately, all I screamed was "AHHH!" and it only took a moment to grab "Gregory" (as my son has since named "him") with a pair of pliers, run upstairs, and deposit him in the woods.
I put a piece of vectorboard over the vent holes after that.
It's not unusual for bugs to be attracted to dishwashers because dishwashers are moist and warm. Unfortunately, I don't know what design engineers can do to prevent them from getting in, though.
My thirty year old Kitchen Aid dishwasher had a good screen to keep stuff out of the pump, and the design was such that the heavier stuff would accumulate in a wide channel below the screen so that the filter did not get dirty very often. In addition, the design of the filter system was such that the return water would slow as it approached the filter, assisting the chunks to fall into the collection channel, which was quite easy to wipe clean. It seems that the engineers responsible for that design knew a bit about fluid dynamics and how to drop stff out of a stream before it even reached the filter. Very good engineering.
As for the problems with the transformers and the fire ants eating the insulation, my conclusion is that those monsters came stright up from hell a while back and are never content unless they are causing problems.
I never intentionally use or purchase any transformers that include an internal nonreplacable device as mentioned. I have bypassed those devices in several transformers and never had any ill effects because of it. My impression is that the thermal protectors are very cheap quality and so some of them open at a temperature below the specified heat, rendering the product failed. So if a transformer has an external fuse, or other protection, removing the thermal fuse is not a problem that would cause a hazard.
Most transformers of this type need to have such a device to get their UL/CSA approvals. The unfortunate part about this particular one was the manufacturer's choice to use one embedded deep within the windings (presumably at the potential hottest spot), and to use a non-self-resetting one. This unit was potted, so I wasn't about to try to rewind it! A good example of what happens with the latter (self-reset) type can be found in most lamp ballasts: we've all seen fluorescent and other discharge-type lamps that SLOOOOOOOOOWLY cycle on and off all by themselves as the ballast and/or lamp gets old and triggers the device during "normal" operation. It's especially annoying in vapor-discharge (mercury or sodium) street lights (even more so if it's the one right beside you bedroom window!). However, I suppose that's better (from a safety standpoint) than a street light that's out and stays that way!
"A good example of what happens with the latter (self-reset) type can be found in most lamp ballasts: we've all seen fluorescent and other discharge-type lamps that SLOOOOOOOOOWLY cycle on and off all by themselves as the ballast and/or lamp gets old and triggers the device during "normal" operation. It's especially annoying in vapor-discharge (mercury or sodium) street lights (even more so if it's the one right beside you bedroom window!). "
Actually in this case it isn't a reseting cutout but a fundamental property of the gas discharge lamp. As the lamp ages the voltage required to maintain the arc discharge rises, eventually (about 20k-25k hours for HPS lamps, about 3/4 that for mercury & metal halide) reaching a level higher than the max running voltage available from the ballast and the arc extinguishes. The discharge tube then cools to a point that the arc can be restruck by the ballest whereupon the lamp's arc tube reheats and the cycle repears. The solution is to relamp the fixture.
From Dell / Intel® New Paradigms in Design Work Scott Hamilton, vertical market strategist for Dell Precision workstations, 5/2/2013 3
Early in my career, I worked as a draftsman and remember the days of drawing on vellum with numbered pencils and Mylar with plastic lead. This was a fun experience in the sense that I ...
I've been using workstations for more than 10 years and love finding ways to get more performance from my system. With demanding professional applications that require more power each ...
A lasting memory from my first job as an engineer in an auto assembly plant is standing on hard concrete at six in the morning, vending-machine coffee clutched in hand, listening to ...
A quick look into the merger of two powerhouse 3D printing OEMs and the new leader in rapid prototyping solutions, Stratasys. The industrial revolution is now led by 3D printing and engineers are given the opportunity to fully maximize their design capabilities, reduce their time-to-market and functionally test prototypes cheaper, faster and easier. Bruce Bradshaw, Director of Marketing in North America, will explore the large product offering and variety of materials that will help CAD designers articulate their product design with actual, physical prototypes. This broadcast will dive deep into technical information including application specific stories from real world customers and their experiences with 3D printing. 3D Printing is
To save this item to your list of favorite Design News content so you can find it later in your Profile page, click the "Save It" button next to the item.
If you found this interesting or useful, please use the links to the services below to share it with other readers. You will need a free account with each service to share an item via that service.
Tweet This
4 
