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Ot: Dishwashers

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tooki:

--- Quote from: Halcyon on December 26, 2020, 09:02:48 am ---
--- Quote from: Alex Eisenhut on December 23, 2020, 07:04:46 am ---A thought occurs. The rinse-aid is loaded into a compartment and is typically good for dozens of loads.

Why isn't the detergent also this way? Why not load the whole door (it is mostly empty, no?) with a big tank of gel-type detergent?

--- End quote ---

I'm guessing because most detergents used in dishwashers are powder-based. Powder tends to cake up with moisture (particularly from the drying cycle) so it's hard to store in anything other than an airtight container for long periods. Rinse aid is liquid and even if a little dilution occurs, it will still dispense.

Also, why make things more complicated with more moving parts? The operator can just tip a little detergent in each time. Takes almost no effort.

--- End quote ---
Well, the main reason I can think of, beside convenience, is that people tend to overdose detergents, when given the chance. A properly designed dispenser could dispense just the right amount.

With that said: a) tabs/pods reduce this, and b) automatic dispensers so far haven't lived up to the hype.

My best friend and my mom each have a Miele (clothes) washer with an automatic detergent dispenser. The European model can use canisters you fill with your own detergents and/or softeners, or with Miele's own detergent system; the US model supports only the Miele detergent system. Miele's system sounds good on paper: it uses two liquids (one detergent, one liquid peroxide bleach) to overcome the problem of oxygen bleach degradation in liquid detergents. (This is why powder detergents are better at whitening: the oxygen bleaches are much more stable in dry form.) But independent performance tests show it doesn't actually work as well as an ordinary powder detergent. :/

The problem I see with automatic powder dispensing, whether with clothes washers or dishwashers, is moisture. I reckon it'd be extremely difficult to design a dispenser that is airtight enough to not allow in moisture from the machine, since seals would likely end up with powder on them, dramatically reducing their effectiveness. (Miele sorta does this, with a "powerdisk" powder detergent cartridge. I'm not sure how it's sealed, though, I just know the manuals say to clean the seals when changing the cartridge, and to dry everything well when doing so, lest the detergent clump up.)


Where automatic detergent dispensers are completely the norm is in commercial machines. But as you know, the common "tank" style of commercial dishwashers operate on fundamentally different principles from household dishwashers, relying on harsher chemistry and very high temperature wash water (which isn't drained between loads), optimized for newly-soiled dishes, rather than the dried-on foods of household dishes (where dishes may accumulate for days before being run).

Alex Eisenhut:
That's why I said gel-type. I don't see the problem in removing one moving part, the wax motor or whatever opens the latch, and replacing it with a gravity feed detergent dispenser. Or I'm sure there's a clever mechanical thingy that lets you use the pressure of the water supply to move things along.

Then the dishwasher can use its existing turbidity sensor and dose in more detergent if needed.

tooki:
Dispensing liquids is easy, as the rinse aid dispenser in every dishwasher demonstrates. But you definitely want it controlled by the MCU, not run by a “dumb” mechanism like a wax motor. (How would it dispense only in the wash phase, and not in the drying phase which gets equally hot?) Modern appliances rely on MCU programs to carefully control their cycles in ways simple mechanical approaches cannot do.

Commercial dishwashers (both tank type and “fresh water” type, i.e ones using the same principle as household dishwashers) generally have detergent dispensers available (often standard), and they invariably use liquids, as they’re easy to pump from a jug and are easy to dose accurately. The modified dishwashers sold for laboratory/medical use (e.g. to clean lab ware, dental tools, etc, before sterilizing in an autoclave) also use liquid detergents.

P.S. Μy hunch is that the viscosity in dishwasher gels is purely artificial, for marketing and/or convenience purposes. Commercial dishwasher detergent liquids are not particularly viscous.

james_s:

--- Quote from: Nusa on December 24, 2020, 06:15:52 am ---I like the Bosch brand also, mainly because of the integrated water softener that is not found in most dishwashers in the US. However, it's difficult to find dishwasher salt in the stores here. Luckily, pool salt seems to be the same thing and works wonderfully. I got a 50 pound bag on sale for $5 that should take me a decade to use up.

--- End quote ---

Bosch dishwashers are nice when they work, extremely quiet. I've had to fix several of them though and they're kind of a pain to work on and at least the ones I worked on had some questionable designs. Most recently I fixed one my friend had, the pump failed and the problem turned out to be the face of the impeller sheared off the backing, I'd never seen that happen before. About a year later he replaced the whole thing because it started leaking somewhere else.

tom66:
Contrary to Alec's (Technology Connections) comments on Bosch dishwashers, the system is far superior to American dishwashers, in my opinion!

Bosch machines use a filter to catch big waste, which means the biggest waste can be siphoned off and cleaned every 30 or so uses (~3 months) into the general waste.  This big waste is not macerated and recirculated within the machine, which clogs pipes and adds dirt to dishes being rinsed.  You should remove big waste from dishes before loading them; I think this is true of all dishwashers.  And while pre-rinsing is a waste of time (why people still do this baffles me),  you should make some effort to take the largest waste off the plates as the machines are not designed to remove these effectively.

The Bosch dishwashers (and many other European dishwashers) do support a cold pre-wash, by means of putting some detergent in the bottom of the tub.  However, there is probably no need.  The first thing the machine does is rinse the dishes with cold water.  This cold water rinse is used to remove initial dirt and contamination from the dishes and a turbidity sensor then measures how dirty this pre-rinse water is.  If it is dirtier, then the subsequent cycles are extended and the heat time is increased, which while not exactly the same as dosing the dishes with more detergent gives the detergent more time to work.  This is then followed by the hot rinse cycle where hot water is used to remove detergent from the plates, and as part of the drying cycle the plates are made to get as hot as practical with the cold, insulated stainless steel tub acting to dry the plates.  This is remarkably effective:  no second heating element is used (only the water heater) and, unlike systems with that heating element, there is no risk of melting plastic plates, utensils etc., as they are not directly exposed to the element,  but plates come out almost perfectly dry at least when the machine has been allowed to run overnight and is unloaded in the morning.

The machine is also very water-efficient, on its economy setting using only 6 litres of water in total, which is some 1/10th of what an average hand-washer uses.

I have never had any problem with the Finish tablets myself, and in the UK I can purchase 144 tablets (2x72pk) for about £12 including VAT, or around 9p/wash.  The dishwasher itself uses 1.4kWh of electricity on the 'Intensive 70C' setting which at standard rates is ~2x the tablet cost;  I however run the dishwasher whenever possible during my 5 hour off-peak period where electricity is 5.5p/kWh.

I have actually found poorer results from other tablets, but admittedly haven't tried powder detergents in this particular machine.

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