Many valves are controlled manually with a handle attached to the stem.
Valves can also be controlled by actuators attached to the stem.
They can be electromechanical actuators such as an electric motor or solenoid, pneumatic actuators which are controlled by air pressure, or hydraulic actuators which are controlled by the pressure of a liquid such as oil or water.
Actuators can be used for the purposes of automatic control such as in washing machine cycles, remote control such as the use of a centralised control room, or because manual control is too difficult such as when the valve is very large.
Pneumatic actuators and hydraulic actuators need pressurised air or liquid lines to supply the actuator: an inlet line and an outlet line.
When a high water level is reached, a mechanism shuts the valve which fills the tank. In some valve designs, the pressure of the flow fluid itself or pressure difference of the flow fluid between the ports automatically controls flow through the valve.Źródło: https://en.wikipedia.org/wiki/Valve
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. 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. 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.Thicker walled pipe generally implies greater durability and higher pressure tolerances. Wall thickness does not affect pipe or tubing size.1/2" L copper has the same outer diameter as 1/2" K or M copper.The same applies to pipe schedules.As a result, a slight increase in pressure losses is realized due to a decrease in flowpath as wall thickness is increased.In other words, 1 foot of 1/2" L copper has slightly less volume than 1 foot of 1/2 M copper.Źródło: https://en.wikipedia.org/wiki/Plumbing