Employment contracts signed 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.
Plumbing - about materials
Water systems of ancient times relied on gravity for the supply of water, using pipes or channels usually made of clay, lead, bamboo, wood, or stone. Hollowed wooden logs wrapped in steel banding were used for plumbing pipes, particularly water mains. Logs were used for water distribution in England close to 500 years ago. US cities began using hollowed logs in the late 1700s through the 1800s.8 Today, most plumbing supply pipe is made out of steel, copper, and plastic; most waste (also known as "soil")11 out of steel, copper, plastic, and cast iron.11
The straight sections of plumbing systems are called "pipes" or "tubes". A pipe is typically formed via casting or welding, whereas a tube is made through extrusion. Pipe normally has thicker walls and may be threaded or welded, while tubing is thinner-walled and requires special joining techniques such as brazing, compression fitting, crimping, or for plastics, solvent welding. These joining techniques are discussed in more detail in the piping and plumbing fittings article.
Steel pipes in plumbing
Galvanized steel potable water supply and distribution pipes are commonly found with nominal pipe sizes from 3?8 inch (9.5 mm) to 2 inches (51 mm). It is rarely used today for new construction residential plumbing. Steel pipe has National Pipe Thread (NPT) standard tapered male threads, which connect with female tapered threads on elbows, tees, couplers, valves, and other fittings. Galvanized steel (often known simply as "galv" or "iron" in the plumbing trade) is relatively expensive, and difficult to work with due to weight and requirement of a pipe threader. It remains in common use for repair of existing "galv" systems and to satisfy building code non-combustibility requirements typically found in hotels, apartment buildings and other commercial applications. It is also extremely durable and resistant to mechanical abuse. Black lacquered steel pipe is the most widely used pipe material for fire sprinklers and natural gas.