question: How do water faucets work with going back and forth from hot to cold water?
comment: It depends on the type of faucet you have, but in general, it let's both cold and hot water in. If you adjust it to hotter, it's just letting in more hot water and less cold water.
passages: Most Moen kitchen, washbasin, and bathtub/shower faucets are of the single-handle design, and almost all have used the same basic water-controlling cartridge since the 1960s. Known as the Moen 1225, it is a plastic (older versions were brass) cylinder approximately 4 inches long by 3/4 inches in diameter. As the "engine" in most Moen single-handle faucets, it has undergone at least two revisions since its inception though newer versions remain compatible with older faucets. Pulling up the stem of the cartridge opens the water supply; rotating toward the left opens the hot water passages while rotating to the right opens the cold water passages (using the standard North American convention of the hot water control on the left).
   Section::::Faucet design.
   In the event of an unplanned reduction of the cold water supply; to prevent scalding or the flow of higher than pre-set temperature, the patent also includes a thermo-responsive device capable of instantly cancelling the operation of the solenoid valve which supplies the hot water. 
  
  "10. A liquid flow control device as claimed in claim 1 wherein the outlet has a thermo-responsive means capable of cancelling the operation of the solenoid operated valve which controls the hot water.
   Wareham initiated electronic controls of water flow for domestic, commercial, medical and industrial uses. As described in the following extracts from United States Patent 4,428,422 claims, the system is activated by various electronic sensor means to achieve ‘no touch’ flow control to prevent bacteria transfer in areas such as hospital use or food preparation. It includes an electronic thermo-responsive control to prevent scalding, or water flow exceeding pre-set safe temperatures and by use of pre-set electronic timer devices, prevention of flooding and waste of water..
   The book describes a dispenser for hot and cold water, where the two outlets alternate, one discharging cold water and the other hot, then vice versa repeatedly. It also describes a vessel with a basin by its side where, when cold water is poured into the top of the vessel, it discharges from the mouth of a figure into the basin; when hot water or another liquid is poured into the basin, the same quantity of cold water is discharged from the mouth of the figure.
   The result is that the top pipe which received hot water, now has cold water leaving it at 20 °C, while the bottom pipe which received cold water, is now emitting hot water at close to 60 °C. In effect, most of the heat was transferred.
  
  Section::::Three current exchange systems.:Countercurrent flow—almost full transfer.:Conditions for higher transfer results.
  
  Nearly complete transfer in systems implementing countercurrent exchange, is only possible if the two flows are, in some sense, "equal".
   Water for baths, sinks and basins can be provided by separate hot and cold taps; this arrangement is common in older installations, particularly in public washrooms/lavatories and utility rooms/laundries. In kitchens and bathrooms, mixer taps are commonly used. In this case, hot and cold water from the two valves is mixed before reaching the outlet, allowing the water to emerge at any temperature between that of the hot and cold water supplies. Mixer taps were invented by Thomas Campbell of Saint John, New Brunswick, and patented in 1880.
   This is a popular arrangement where higher flow rates are required for limited periods. Water is heated in a pressure vessel that can withstand a hydrostatic pressure close to that of the incoming mains supply. A pressure reducing valve is sometimes employed to limit the pressure to a safe level for the vessel. In North America, these vessels are called "hot water tanks", and may incorporate an electrical resistance heater, a heat pump, or a gas or oil burner that heats water directly.
   BULLET::::2. By acting as an operating control on a three-way powered mixing valve or proportional injection pump system that modulates the supply distribution hot water temperature. The mixing valve or mixing pump system recirculates the return water temperature and adds proportionally supply hot water from the boiler for tempering to achieve the desired supply water temperature. Another method is to adjust boiler temperature from thermostat activity. This indoor reset control. It is more responsive to real needs inside the building.
   Section::::Function.:Conservation and energy reduction.
  
  Because the aerator limits the water flow through the faucet, water use is reduced as compared to the same time of flow without an aerator. In the case of hot water, because less water is used, less heat energy is used.
  
  Section::::Function.:Perceived water pressure.
   Section::::Initiation.:Flux.
   The control system can be made to modulate the supply water temperature in two different ways:
  
  BULLET::::1. By acting as an operating control on the boiler burners, either modulated on/off, high/low fire, or fully modulating fire, depending on the burner construction. When modulating the actual boiler temperature lower, water temperature needs to have a low limit and be maintained above the flue gas condensation temperature for non-condensing type boilers, typically above . Condensing type boilers can be made to operate at temperatures below the flue gas condensation limit and raise stated efficiencies from the range.
   This system can be difficult to balance due to the supply line being a different length than the return; the further the heat transfer device is from the boiler, the more pronounced the pressure difference. Because of this, it is always recommended to: minimize the distribution piping pressure drops; use a pump with a , include balancing and flow-measuring devices at each terminal or branch circuit; and use control valves with a at the terminals.
  
  Section::::Two-pipe reverse return system.
   Water will flow faster when the handle is in the upright position. The water is aerated which allows the water to come through the spout at a faster rate.
  
  Section::::Water source.
  
  Water dispensed from water coolers may originate from many different sources, but are often classified into two major categories, namely natural mineral and spring water, and purified water.
  
  Section::::Water source.:Natural mineral and spring water.
   There can be many variations on the shell and tube design. Typically, the ends of each tube are connected to plenums (sometimes called water boxes) through holes in tubesheets. The tubes may be straight or bent in the shape of a U, called U-tubes.
   When the handle is pressed, cool tap water flows into the tank and displaces the near-boiling water, which flows out of the spout. On releasing the handle the valve closes and hot water stops flowing. The cool water is then heated to up to about ready for use however the Quooker PRO-VAQ water tank heats the water to meaning the water flows out of the spout at . It is widely acknowledged that the inventor of the boiling water tap was the founder of Quooker, Henri Peteri. 
   Section::::Initiation.
   Domestic hot water is provided by means of water heater appliances, or through district heating. The hot water from these units is then piped to the various fixtures and appliances that require hot water, such as lavatories, sinks, bathtubs, showers, washing machines, and dishwashers.
  
  Section::::Fixtures and appliances.
   The hot fluid in the case of the rising film evaporator would be the steam in the shell side and the cold fluid would be the liquid inside the long tubes. In relation to the overall heat transfer rate, there are several key parameters that affect this characteristic specifically in terms of a rising film evaporator.
  
  Section::::Main characteristic and assessments.:Heat transfer coefficients.
   Section::::Initiation.:Stagnation.
   This duration is controlled by the thermotime switch, which is a bimetallic strip based device placed in the water jacket or in the case of an air-cooled engine, in the engine/timing case. When an engine first starts, the coolant temperature is cold and the bimetallic strip is closed, which in turn supplies the cold start injector with current.
   Section::::See also.
  
  BULLET::::- Advanced Metering Infrastructure
  
  BULLET::::- American Water Works Association
  
  BULLET::::- Automated meter reading
  
  BULLET::::- Drinking water
  
  BULLET::::- Electricity Meter
  
  BULLET::::- Flow measurement
  
  BULLET::::- Gas meter
  
  BULLET::::- Meter Data Management
  
  BULLET::::- Public utility
  
  BULLET::::- Utility submeter
  
  BULLET::::- Water conservation
  
  Section::::Further reading.
  
  BULLET::::- American Water Works Association Manual of Water Supply Practices Manual M6, Water Meters — Selection, Installation, Testing, and Maintenance,
  
  BULLET::::- American Water Works Association standards C700-02: Cold-Water Meters—Displacement Type, Bronze Main Case
  
  BULLET::::- American Water Works Association standards C701-02: Cold-Water Meters—Turbine Type
  
  BULLET::::- American Water Works Association standards C702-01: Cold-Water Meters—Compound Type
   There are also some specialized types of registers such as meters with an LCD instead of mechanical wheels, and registers to output data or pulses to a variety of recording and controller devices. For industrial applications, output is often 4-20 mA analog for recording or controlling different flow rates in addition to totalization.
  
  Section::::Registers.:Water meter reading.
   In most countries, there is a standard arrangement of hot/cold taps. For example, in the United States and many other countries, the hot tap is on the left by building code requirements. Many installations exist where this standard has been ignored (called "crossed connections" by plumbers). Mis-assembly of some single-valve mixer taps will exchange hot and cold even if the fixture has been plumbed correctly.
   For baths and showers, mixer taps frequently incorporate some sort of pressure balancing feature so that the hot/cold mixture ratio will not be affected by transient changes in the pressure of one or other of the supplies. This helps avoid scalding or uncomfortable chilling as other water loads occur (such as the flushing of a toilet).
  