Mine actually is more like the one on the right. However, it's kind of a pain when I actually do want to get cold water out of it, because that range is so small.
It would be nice to have such an intelligent faucet, but I fear it would need actual electronics and other gizmos with feedback to regulate the output, and moderate for toilet flushes etc. It seems like such an obvious innovation opportunity that I suspect building regulations may have interfered at some point.
This can be done mechanically with temperature-sensitive alloys. My shower maintains constant temperature without electricity
Yes. I was surprised, but this actually exists and I have one. There's also a (mechanical) lockout preventing you selecting "magma" by accident. With a pair of pliers and a screwdriver you can set this lockout just above your preferred temperature so that a simple twist of the controls puts it back how you like it after using cold water. I love gadgets, but sometimes a simple mechanical solution really is better.
Bimetallic strips: the secret lost technology of the 20th century!
My shower faucet adjusts the temperature automatically so it's the same temperature every time I use it. It maintains the temperature even if some other appliance decides it needs water.
I've seen these faucets in stores and I suspect they haven't caught on much because an upgrade involves taking apart a wall.
I had a Grohe (or HansGrohe, not sure) shower control with separate volume and temperature control. The temperature control was a knob, stayed fixed 99% of the time. A lever on the inside controlled the water volume. Not cheap, but useful. I have seen them called "thermostatic mixers."
We've had them in France since the late 1980s. They're damn handy. Expensive to replace (so I assume expensive to fit), but we've only ever had to replace one since they were fitted. I wasn't even aware they could break.
At my previous house, I had a small ball valve in line with the shower head that was designed for the purpose (hence appropriately chrome plated and such).
It cost me $3, took five minutes to install (including time spent digging around looking for the teflon tape), and worked fine: I could turn the shower down.
This is a solved problem. (I'm going to use "tap" in the following example because I'm British; Merkins should substitute that word with "faucet".) You can do one of two things:
1) Have a mixer tap which a) swivels from one end of a range to another to denote a spectrum of hot vs cold, and b) lifts up to increase the water pressure; or
2) you have two taps, one which controls the temperature, and the other the water pressure.
Either way, you leave the temperature tap the fuck alone. (Well, you turn the temperature down in summer and up in winter, but that's a gradual change.) You keep temperature choice and "I want water on/off now please" separate, as they're two orthogonal things.
What mystifies me is that there is no such thing as a mixer tap in the UK. In most sinks you have a cold tap and a hot tap, which means you can either turn both on, put the plug in, and basically run a small bath at what will end up as the right temperature eventually, or you turn both taps on and run your hands underneath each stream alternately, hoping that you manage to get your hands clean before the hot tap goes from cold to tepid to warm to fucking scalding and you can't stand to have your hands underneath that.
I mean, I can vaguely understand having two separate controls for cold and hot water, but having the water from each come down a separate conduit? That's just bizarre.
Yeah.. that freaks me out every time I happen to be in the UK.
Just figured out that I have to put the OpenID URL in the website field.. that wasn't so obvious (to me).
Erm, it's hard to go into a modern UK home kitchen/bathroom and not see mixer taps.
Regulations mean you can't mix the water in the system, but apart from that..
Specifically I think there has to be a no return valve between the mains and the mixer control. This ensures that whatever crap is in your hot water system can't be flushed into the public drinking water by accident.
But the choice of mixers or not tends to be a style thing. Kitchens in particular are very subject to fashion. For a while white sinks and big brass taps was in, even though it's not terribly practical. Kitchen surfaces are the same, people buy granite or wood even though they're more expensive and harder to look after than the engineered materials that were invented specifically for this role.
I've read that this is the case because UK housing typically had unpressurized hot water- gravity fed from a roof tank- until relatively late. You can't use a mixer tap on that kind of system because the pressures are so different. Add a bunch of inertia, tradition, and the slow upgrade cycles of plumbing, to carry non-mixer taps forward to the present day.
In the US we call that a proper sink.
Most shower valves that do any sort of compensating are only balancing the pressures between hot and cold. This type has been extremely common for many years. The last time I bought a shower valve (about three years ago), every available model was of the pressure-balancing variety.
They are very simple, and have only one more moving part than a non-compensating valve.
They're simple in function, too: When someone flushes the toilet, turns on a garden hose, or whatever, the pressure drops on the cold side. The valve simply balances this variation by reducing the pressure of the hot side, and the net effect to the end user is that the temperature stays basically the same no matter what else goes on in the house...though the water flow from the shower head may decrease accordingly. (The opposite happens when there's a pressure drop on the hot side...)
But, again, the valve itself has no concept of temperature, only pressure differences.
There -are- temperature-compensating shower valves available, as well as some that handle fluctuations in both temperature and pressure. They are both unusual and dear, and serve mostly to limit water temperature to a maximum of 112 degrees F (far short of JWZ's magma requirement).
There are also general-purpose mixing valves that serve to limit water temperature automatically. These are somewhat unusual in consumer applications, and are generally suited to places with conflicting temperature needs. For instance, a restaurant might use something like this to allow the use of fucking goddamn hot water in the kitchen without there being any chance of Little Johnny scalding his hands in the bathroom...without the need for a separate hot water system.
Regarding electronics and water: I used to live in an apartment that had push-button water. Mounted in the wall beside each fixture (yes, including the shower) was a row of push-button switches. The switches operated a complicated array of 24VAC solenoid valves and manifolds inside of a metal box located under the kitchen sink, which delivered water of the selected temperature to the fixture via a single home-run pipe.
You want cold? Push the blue button. Hot? The red one. Something in between? Pick one (only one!) of the buttons in between. Want less water? Push the button for "less," if that particular fixture was so-equipped, otherwise tough. All done? Hit the button labeled "off."
It worked OK once I patched up some of the ancient wiring and diddled the mixing valves to my preference, but it always seemed a little bizarre and archaic having so few choices for water temperature and pressure. The switches themselves seemed to be holding up just fine.
This is a mandatory feature for my new bathroom, they are expensive, but totally doable.
They do often look pretty "space age" so I suspect they'll look pretty dated in a few years.
I wish we could just have a simple freaking fixture for this...
This is so simple and cheap to fix if you are stuck with one of the single-control shower setups.
Just get one of these:
Alsons Incredible Head Power Shower Head
Elite shower head
The lever or button allows you turn turn down the flow while the temperature is warm enough.
I have to admit it is a conspiracy to waste energy by forcing "hot water = max flow".
This makes sense if you have pressure issues, but otherwise you've got to dump the less-than-hot water lying in the hot water pipe between you and the hot water heater. So turning down the flow just means waiting longer.
Or you can install a recirculating system and avoid this annoyance at the cost of basically running a baseboard heating system all the time (not quite as bad if the pipes are insulated).
You guys are all overthinking this to an incredible degree. The device illustrated on the right doesn't require electronics or heat-sensitive metamaterials, just a screw with nonlinear response. Y axis: angle of rotation. X axis: ratio of hot to cold. Curve: not a straight line.
That only works if the green area is in the same place all the time, which I doubt it is. Pressure variations, temperature variations, manufacturing variations, gradual buildup of scale in the pipes, whatever.
re: crazy materials, a lot of valves like the one pictured (I thought Delta, but apparently ours are 'Symmons-Temptrol') actually include a bimetallic piece somewhere to avoid scalding you when someone flushes a toilet or whatever. But this does not help with the "actually useful" band being shit.
One thing that did help was actually turning down the water heater to the energy-friendly temperature; this reduces the "boil lobsters" band at the top and seems to widen the potentially-comfortable range to the top 1/4 of the dial or so. (Maybe they've been designing them with that assumption since the Carter era?) I'm thinking overly hot water might also make said "temptrol" dingus over-react somehow.
Morning means I somehow forget bimetallics were covered at the top of the thread.
I think I was attempting to connect with "hattifattener"'s post as far as "since that magic exists putting a nonlinear control behind it should not be a big deal."
Relevant Eddie Izzard piece on shower controls