Valves may also be automatic, driven by changes in pressure, temperature, or flow. These changes may act upon a diaphragm or a piston which in turn activates the valve, examples of this type of valve found commonly are safety valves fitted to hot water systems or boilers.
More complex control systems using valves requiring automatic control based on an external input (i.e., regulating flow through a pipe to a changing set point) require an actuator.Źródło: https://en.wikipedia.org/wiki/Valve
The importance of the valves
Valves are found in virtually every industrial process, including water and sewage processing, mining, power generation, processing of oil, gas and petroleum, food manufacturing, chemical and plastic manufacturing and many other fields.
People in developed nations use valves in their daily lives, including plumbing valves, such as taps for tap water, gas control valves on cookers, small valves fitted to washing machines and dishwashers, safety devices fitted to hot water systems, and poppet valves in car engines.
In nature there are valves, for example one-way valves in veins controlling the blood circulation, and heart valves controlling the flow of blood in the chambers of the heart and maintaining the correct pumping action.
Valves may be operated manually, either by a handle, lever, pedal or wheel.
Worth to know
The difference between pipes and tubes is simply in the way it is sized.
PVC pipe for plumbing applications and galvanized steel pipe for instance, are measured in IPS (iron pipe size).
Copper tube, CPVC, PeX and other tubing is measured nominally, which is basically an average diameter.
These sizing schemes allow for universal adaptation of transitional fittings.
For instance, 1/2" PeX tubing is the same size as 1/2" copper tubing.
1/2" PVC on the other hand is not the same size as 1/2" tubing, and therefore requires either a threaded male or female adapter to connect them.
When used in agricultural irrigation, the singular form "pipe" is often used as a plural.7
Pipe is available in rigid "joints", which come in various lengths depending on the material.
Tubing, in particular copper, comes in rigid hard tempered "joints" or soft tempered (annealed) rolls.
PeX and CPVC tubing also comes in rigid "joints" or flexible rolls.
The temper of the copper, that is whether it is a rigid "joint" or flexible roll, does not affect the sizing.7
The thicknesses of the water pipe and tube walls can vary.
Pipe wall thickness is denoted by various schedules or for large bore polyethylene pipe in the UK by the Standard Dimension Ratio (SDR), defined as the ratio of the pipe diameter to its wall thickness.
Pipe wall thickness increases with schedule, and is available in schedules 20, 40, 80, and higher in special cases.
The schedule is largely determined by the operating pressure of the system, with higher pressures commanding greater thickness.
Copper tubing is available in four wall thicknesses: type DWV (thinnest wall; only allowed as drain pipe per UPC), type 'M' (thin; typically only allowed as drain pipe by IPC code), type 'L' (thicker, standard duty for water lines and water service), and type 'K' (thickest, typically used underground between the main and the meter).
Because piping and tubing are commodities, having a greater wall thickness implies higher initial cost.
Where water resources or infrastructure or sanitation systems are insufficient for the population, people fall prey to disease, dehydration, and in extreme cases, death.
Major human settlements could initially develop only where fresh surface water was plentiful, such as near major rivers.
Thicker walled pipe generally implies greater durability and higher pressure tolerances.Źródło: https://en.wikipedia.org/wiki/Water_pipe#Difference_between_pipes_and_tubes
History of water supply and sanitation
Water supply and sanitation has been a primary logistical challenge since the dawn of civilization.
Over the millennia, technology has dramatically increased the distances across which water can be relocated, but the availability of clean and fresh water remains a limiting factor on the size and density of population centers, and is expected to remain so into the foreseeable future.Źródło: https://en.wikipedia.org/wiki/History_of_water_supply_and_sanitation.