Pipes and Fittings


Pipes and fittings

Nowadays, most plumbing pipes are copper, though plastic pipes are often used for waste and plastic pipe is becoming common for supply too.

Copper pipe

Copper pipe is sized by its outside diameter – 15mm, 22mm and 28mm are the most common sizes (equiva­lent to +in, tin, and I in inside diam- eter). Main runs and pipes feeding bath taps are usually 15mm.

Copper pipe can be cut with a fine- toothed hacksaw, or with a special pipe-cutting tool. Care must be taken to cut exactly square and the cut must be filed smooth both inside and out. A pipe cutter tends to leave a burr inside the pipe – this should be filed off.

Copper pipe can be bent by hand but it must be supported by bending springs or it will kink. These are stiff metal coils of the appropriate dia­meter pushed into the pipe where the bend is to be made.

For small plumbing jobs, using pipes up to 22mm, beriding springs are probably all that you need. For large plumbing jobs and larger pipes a bending machine is worth hiring, though it requires practice to get the bend in the right place in the pipe.

Bends are better than fittings for altering the direction of a run – bends are cheaper and allow a smoother flow. Special bendable copper pipe is useful for the odd bend, at taps for instance, but very expensive to buy.

Joining copper pipes

The main methods of joining copper lengths of copper pipe are to use compression joints which are fitted to the pipes using spanners —an olive makes the watertight seal – or capil­lary joints which are soldered on to the pipes.

There are two types of capillary fitting. The solder-ring fitting is most suitable for d-i-y, this has its own, built-in, supply of solder which whenheated flows to fill the gap between the fitting and the pipe ends. End feed fittings are similar but with these a length of solder wire is melted at the mouth of the fitting and allowed to creep into the gap.

For plumbing water pipes either capillary or compression fittings can be used. Compression fittings are usually first choice for a novice, they’re fairly easy to make, can usually be undone and reconnected and if they leak, the leak can often be stopped by slightly tightening the fitting. (They’re also useful if you have to joint into stainless steel pipes.) Capillary fittings are neater and chea­per, but require a little practice to become expert. A leaking capillary joint often means that the solder hasn’t flowed properly and in this situation the joint generally has to be sawn apart and replaced. Capillary fittings are required for gas plumbing.

Push-fit plastic connectors are a third choice for water plumbing with15mm and 22mm pipes. These plastic connectors are very easy to fit and can easily be undone and refitted, but they are more expensive than the other types of fittings. To make the joint smear the pipe end with lubricant and push it into the connector – a plastic ring makes the watertight seal and a grab-ring holds the pipe firm.

There are many different types of fitting with either capillary or com­pression joint ends: straight coupl­ings for Joining two lengths of pipe together in a straight line; elbows and bends for joining two lengths together at an angle (usually a right angle); tees for joining a branch pipe; and adaptors for joining pipes to taps. Merchants often stock only the most common ones.

Some fittings, such as taps for garden hoses and washing machines, have a screwed end. These fittings can have different sizes of screw thread – in BSP (British Standard Pipe) is the most common. There are a number of ways of making a water­tight joint with these fittings. The simplest is to wrap PTFE tape around the male thread before screwing it into the female part of the fitting. But PTFE tape will not seal large threads. For these, smear a small amount of jointing paste on to the threads fol­lowed by a few strands of hemp (which looks like unravelled string) before screwing the joints together. Screwed fittings which may need to be undone have a washer to make the watertight joints.


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Adding to copper pipes

Joining a new pipe to existing old pipework usually means forming a branch – often by making a tee joint. If the existing pipes are copper and metric sizes there’s no problem, but if the existing copper pipes are the old imperial sizes a special adaptor may be needed to connect the new piece of metric pipe to the old imperial one. Capillary fittings almost always need adaptors; with compression fittings only 22mm pipes (joined to gin) do.

As the actual sizes are only slightly different it is difficult to tell whether old pipework is imperial or metric just by looking so it’s worth having some adaptors in stock. Joining to pipes of other materials can be tricky, es­pecially copper to lead joints – these are best left to a professional. If your house contains much lead piping it may be better to have it stripped out.

Plastic supply pipes

Plastic pipes in 15mm, 22mm and 28mm sizes are now available for both hot and cold water supplies and are also approved for use in central heat­ing systems. Which? has not tested these yet, but they look set to be the d

i-y plumbing material of the future.

The pipes are made of rigid plastics and joined to fittings by the solvent- weld method as described for waste pipes, except that the ends do not need to be chamfered and you push the pipe into the fitting with a slight twisting motion. Pipes are not bendable and fittings are required atall changes of direction.

Although the pipes can carry hot water, a length of copper pipe is required at the outlet of a boiler (or other heat source). Adaptors are avail­able to join plastic to metal pipes and fittings. The pipes must be well supported along their length at a minimum of 500mm for horizontal runs; lm for vertical runs. Thought must be given to the expansion that will occur as the pipes heat up. At each end of short runs (under 3m) leave an expansion gap in the joint of about 3mm. In longer runs exceeding lOm, an expansion loop must be turned somewhere in the length.

Plastic waste pipes

Plastic pipe is easily cut with a knife or a fine-toothed hacksaw. There are two methods of joining. All pipes can be joined with push-fit connections which have rubber sealing rings (‘0’ rings) to make the seal. To make a joint, smooth off the pipe ends and chamfer the outer surfaces to about 15 degrees. Smear with lubricant, push into con­nector and then withdraw slightly to allow for thermal expansion – consult the brand instructions.

Solvent-weld joints are the alter­native (though not all pipes are suit­able for this). To make a solvent-weld joint wipe the chamfered ends and the inside of the connector with a degreas­ing cleaner. Coat with solvent cement, push together and leave undisturbed for a few minutes. Surplus cement is not removed.


A compression joint File the end of one piece of pipe smooth, pass the cap nut from the fitting over it, smear the end

with an approved jointing paste and push the olive on to the pipe. Then push the fitting over the end of the pipe

Prepare the end of the other piece of pipe in the same way – with jointing paste and an olive – and push this into the fitting.

Tighten the fitting with spanners. Do not overtighten: if there’s a small leak, tighten a little more.



Measure, by pushing in a pipe or with a ruler, the distances ‘a’ at each end – it’s the length of pipe which can be pushed into the fitting. Subtract 2 x ‘a”from

the overall length to get b Carefully cut the length b from the pipe at the point where you want the branch to start. To fit the tee connector, it will

probably be necessary to remove some pipe clips, so that the pipes can be pulled slightly out from the wall.

Fix the connector, as any other joint. Fit the branch pipe into place: with a capillary fitting, do this before any soldering.

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