Wikipedia about Valves
A valve is a device that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure. The word is derived from the Latin valva, the moving part of a door, in turn from volvere, to turn, roll.
The simplest, and very ancient, valve is simply a freely hinged flap which drops to obstruct fluid (gas or liquid) flow in one direction, but is pushed open by flow in the opposite direction. This is called a check valve, as it prevents or "checks" the flow in one direction. Modern control valves may regulate pressure or flow downstream and operate on sophisticated automation systems.
scope of work performed by a plumber
Persons employed as plumbers can sign various contracts of employment. They work full-time in a variety of plants, hydraulic or sign contracts-orders for certain services. Some plumbers also run his own business, under which perform minor plumbing services. Nowadays, self-employed persons often assume hydraulic websites, which include information on the services rendered by them and their price list. They also by posting information about their activities on bulletin boards, and even spread leaflets around the city to encourage use of their services. So they can get regular customers, who will often benefit from their services.
range of hydraulic works made in different sizes towns
Hydraulic works carried out in the towns of different sizes have different scope. They can be carried out on behalf of local authorities, if any part of the village needs to be connected to the municipal sewer system or the village was flooded by torrential rains. At the same time the hydraulic assistance can apply the owners of private houses, in which there have been some failures. Depending on the type of failure, they can order the execution of hydraulic works in normal mode, or call the emergency hydraulic. Such hydraulic ambulance is able to reach a flooded home, even during the weekend. While minor work will be done by appointment convenient for the homeowner term.