Plumbing

The art or science of conveying stuff around using pipes. Sometimes metaphorically cf.Internet Plumbing.

The name derives from the Latin plumbum through OFr plomb meaning lead [ref SOED]. Nowadays lead is almost completely absent from pipework, although part of the traditional plumbing craft training is sheet leadwork.

Water

In general 'Plumbing' refers to hot and cold water systems.

Hot Water

Is made from cold water by Domestic Hot Water Systems

Cold water

is best for drinking

Gas

Plumbing for Gas is more commonly referred to as 'Gas Fitting' or 'Gas Installation'. It is regulated by law: specifically the Statutory Instrument known as the Gas Safety (Installation and Use) Regulations 1998

Pipework

Copper

Copper pipes are joined by soldering, using a compression fitting, or pushfit connectors. Some fittings for soldering come ready locaded with solder these are known as Yorkshire or Solder ring fittings.
Chromium plated copper pipe can connected either by removing the chromium or by using compression fittings which are also sold chrome plated.
When copper comes into damp cement, concrete or mortar it may be liable to corrode. This would seem to be related to the composition of the concrete etc: the Copper Development Association in an article "Is There A Problem With Embedding Copper Tube In Concrete?" states:

According to the Portland Cement Association the interaction of copper with both dry and wet concrete should not cause a corrosion concern. However, copper should be protected when it comes in contact with concrete mixtures that contain components high in sulfur, such as cinders and fly-ash, which can create an acid that is highly corrosive to most metals including copper.

For this reason it is good practice to wrap the copper in PVC or grease impregnated (aka "Denso") tape. Specific regulations apply to copper pipe used for carrying gas under the Gas Safety (Installation and Use) Regulations (1998), and pipes buried in floor screeds.

Long runs of copper pipe in concrete are liable to break due to differential thermal expansion.
When cemented or plastered over, "Denso" tape or other flexible wrapping should be used to avoid expansion stresses.

Biological Effects

A claimed benefit of the use of copper in Domestic Hot Water (and possibly also Central Heating) systems is that it has antimicrobial effects against, amongst others, the organism that causes Legionella
Fishtanks should not be filled with water from newly fitted copper piping, as levels of copper in the water from new piping are generally high enough to kill fish.

Plastic

MDPE

Medium Density PolyEthylene is coloured blue for water services or yellow for gas. Black MDPE is also found in older cold water service installations. It is available in inside diameters of 20, 25, 32mm and larger sizes. It is intended to be buried and should not be used for permanent installations where it is exposed to sunlight as UV will degrade the material (although blue MDPE is often run on the surface for temporary installations on building sites etc.) It is usually used for incoming services. It is not suitable for hot water. It is invariably supplied in rolls of various lengths.

PEX and PB

cross-linked polyetheylene (PEX) and Polybutylene (PB) are made to the same outside diameters as copper pipes (but have a smaller inside diameters). It is commonly available in diameters of 15mm and 22mm, with 10mm and 28mm also found.

PB is less springy than PEX, though some makes are more flexible than others.

It can be used for hot and hold water services including central heating.

Barrier pipes have a metallic film sandwiched between inner and outer PB or PEX layers to reduce permeability of the pipe to gases, especially oxygen which is responsible for corrosion in heating systems. See Central Heating for further discussion.

They are usually supplied in a coil but some can be bought in straight lengths.

MDPE, PEX and PB pipes require the use of the correct support stiffeners (some are stainless steel others are plastic) at every end. These keep the pipe from pulling out of fittings.

ABS and PVC

Acetyl Butyl Styrene and Poly Vinyl Chloride pipes are used in 'solvent weld' systems for overflow, waste and drainage pipes. Waste sizes are nominally 32mm, 40mm and 50mm but are actually larger than nominal and not interchangeable with push-fit (although compression fittings can be used with either type). ABS and PVC are also used for rainwater and soil, vent and drain pipes. Soil, vent and drain sizes are interchangeable with push-fit pipe. Overflow (21.5mm nominal) is sometimes found in slightly larger sizes in old pipework which can make extension of existing overflow systems with new materials difficult.

PolyPropylene

Polypropylene is not solvent-weldable. It us used in overflow, waste and soil, vent and drainage pipework. PP waste pipes are made to actual sizes of 32mm, 40mm and 50mm, to be joined by push-fit or compression fittings.

Iron/Steel

These are used for compressed air and still used for gas supply pipes, and for heating pipework in larger commercial and industrial systems. They are usually only found in wet pipework in older domestic installations.
They are installed by cutting stock tube to length and then threading the ends with a die.
A selection of fittings are available for joining the threaded ends together.
The threads conform to an international standard that is a metric adoption of the imperial British Standard Pipe.
The letter R designates this so R0.75 means a 3/4" BSP thread.
The threads can be cut onto a slightly tapered pipe end or parallel.
Cast Iron is used for older waste and drainage pipes.

Stainless Steel

This is found in various forms:

As a direct substitute for copper pipe (but which can only be joined with compression fittings). This is found in some domestic installations dating from the time of a copper shortage during the late 1970s.
Equivalent to mild steel pipe. Used when greater strength or corrosion resistance than steel is required. Used when food grade hygiene standards are needed.
As corrugated semi-rigid (bendable) pipes for gas:
- Short bare stainless steel pipes with pre-attached terminations (known as "Anacondas") for connecting gas meters to incoming gas mains.
- Continuous roll pipe with a yellow polyethylene sheath (known as "TracPipe") which requires special fittings to join and terminate.

Copper plated Steel

Formerly used as copper pipe substitute in the 70s. The finish is copper but the pipe is magnetic.

Lead

Lead piping is no longer installed although some is still found in service. It is found particularly in water pipes in pre-1960 houses, often in the pipe from the street to the main indoor stopcock, and sometimes in tails to taps and WCs etc. It is also sometimes found in connections into and/or out of gas meters.

Health

Water running in lead pipe can leach the metal producing significant levels of lead in the water, causing a heaalth hazard to those ingesting the water (through drinking it or using it for cooking). Naturally occurring chemicals in some sources of water can exacerbate this problem. It used to be common wisdom to run the water for a minute or so first thing in the morning after water had been standing in the pipes overnight, before filling a kettle (or otherwise drawing the water for drinking).

In hard water areas however scale usually forms inside the pipes and prevents water contacting the lead directly, reducing leaching to low and generally not problematic levels.