Page 121 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

Chapter 2 Common processes and techniques

Compression joints

There are a number of different manufacturers of compression joints for low
carbon steel pipes. They incorporate a rubber compression ring to ensure a leak-
free joint. They tend to be rather expensive but can save time on installation
costs. They are often referred to as transition fittings.

Low carbon steel compression fittings can be used on new installations, pipe
repair and pipework extensions on the following installations:

● water (hot and cold water, central heating systems)
● gas (natural gas, LPG)
● oil
● compressed air.

They have several advantages to screwed fittings:
● very versatile connection suitable for connecting LCS pipe to different pipe
materials, such as copper and lead
● quick and easy to make joints
● no special tools necessary
● no threads on steel pipe required.

Plastic pipe

Plumbers should understand the properties of the types of plastics they
use to prevent mistakes being made during their installation. Plastics have
revolutionised modern plumbing systems but it is all too easy to use plastics
for what they are not designed. There are two main types of plastics used in
plumbing:
1 those plastics that can be used for hot and cold water supply and central
heating services (plastic pressure pipe), such as:
● polyethylene (PE)
● polybutylene (PB-1)
2 those plastics that can be used for sanitation, drainage and rainwater
systems, such as:
● polyvinyl chloride
● acrylonitrile butadiene styrene (ABS)
● polypropylene.

Plastic pressure pipe: polyethylene (PE)

PE is used extensively in the plumbing industry for mains cold water pipes. Two
grades are used below ground on cold water services:
1 medium-density polyethylene (MDPE), manufactured in accordance with the
requirements of BS EN 12056-2:2000; it is blue in colour
2 high-density polyethylene (HDPE); this was used until the mid-1980s for
mains cold water pipes until superseded by MDPE; it is still manufactured but
is not used as extensively as MDPE; coloured black, it is available in grades A,
B, C and D.

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