I wonder if I'll have these separate taps in my student flat. Do these separate taps just occur in kitchens and or bathroom sinks or do they also appear in bathtubs?
Have a read through my post right at the top of this thread. You'll find separate taps on bathtubs to be very common, except where they also feed an integral shower attachment. Kitchen sinks are the most common application of mixer taps here, and even then there are plenty of old ones still in use with separate faucets.
It would go from 'almost right' to '100% hot' with just a milimeter of a turn.
This is probably where the wrong type of mixer tap has been used for the system. I described the plumbing arrangements in more detail at the top of this thread, but I'll recap. When it comes to a wash-basin or bathtub there are several arrangements you can encounter:
1. The "traditional" system in which both hot and cold are fed from the cistern in the attic. Both are therefore at the same low pressure and a conventional mixer tap can be used.
2. The "high-pressure" system, most usually associated with the modern British combi-boiler which heats water on demand as it passed through. There is no separate storage cistern, and thus both hot and cold outlets are at the same high pressure. Again, a conventional mixer can be employed. More recently still, we've started to get pressurized hot-water storage systems which also give the same high pressure at both outlets -- This is similar to the standard American arrangement.
3. A hybrid system in which the hot water comes from an open storage cistern in the attic, and is thus at low pressure, but the cold comes directly from the supply and is at a much higher pressure. This can be found in rural properties, homes where plumbing has been altered over the years, or sometimes just where it fitted more conveniently with the design.
Even with the traditional system where
most of the cold taps come from the cistern in the attic, the cold tap on the
kitchen sink was always connected directly to the supply to provide a source of clean, unstored water for drinking and cooking.
It's where you get this combination of high-pressure cold and low-pressure hot that the problem arises. The conventional mixer tap behaves in just the way you describe. Cracking the high-pressure cold open just
slightly more can often overwhelm the low-pressure hot to the extent that it changes from scalding to freezing very quickly.
That's why kitchen mixers here are designed with concentric tubes in the spout. The water doesn't actually mix anywhere within the tap or spout at all. All the mixing is done as the water
leaves the concentric spouts, thus obviating the problem of the pressure differential. If somebody uses a conventional mixer in this position, then control becomes very difficult.
I often wondered if there was some other adjustment that could help balance things...
Not directly. Obviously if both hot and cold are fed from the same cistern or both from the same supply line then the pressure will always be the same anyway.
The only really effective way to use a conventional mixer with different pressure supplies is to use an intermediate pressure-equalizing valve. This would be the only way for a shower, for example, where obviously the hot and cold need to mix before leaving the head.
The pressure-equalizer allows hot and cold to flow through without ever coming into contact, but the pressure of the cold is reduced to match that of the hot. These equalizing valves aren't particularly cheap though, so are rarely used in the average domestic system.
