How to Improve Domestic Plumbing System by Joining New Pipework into Old

Improvements or additions to a domestic plumbing system inevitably involve joining new pipework into old. How you do this depends largely upon whether the existing pipework is made of lead, iron or more modern materials -copper, polythene or even unplasticised PVC.

The principle of joining into existing pipework is quite straightforward. You decide where you will need your new water supply – at a bedroom basin or an outside tap, for example – and then pick a convenient point on the plumbing system to connect up your ‘branch line At this point you have to cut out a small section of the old pipe and insert a tee junction into which the branch pipe will be fitted. That’s all there is to it: laying the branch pipe will simply involve routine cutting bending and joining of new pipe, and final connection to the new tap or appliance at the other end.

domestic plumbing How to Improve Domestic Plumbing System by Joining New Pipework into Old

Before you can begin the job, however, you have to do some reconnaissance work to identify what sort of existing pipework you have. You might be tempted to relate the plumbing to the age of the house, thinking that an old house will have an old system with lead or iron pipework But this isn’t a reliable guide Many old properties have been modernised and so may actually have a more up-to-date system than a house built relatively recently.

Until the 1950s the only types of pipe used in domestic plumbing were lead and iron, but then these were superseded by thin-walled copper piping. Today there are other alternatives too: stainless steel is sometimes used as an alternative to copper, and polythene and UPVC (unplasticised polyvinyl chloride) pipes can be installed for cold water supplies only.

Check the table for the type of pipe you can use. While copper is the most common one for new work, it must never be joined to galvanised iron because of the severe risk of electrolytic corrosion of the iron if the galvanising is not in perfect condition

First things first

Before cutting into a pipe run you’ll first have to turn off the water supply to the pipe and then drain it by opening any taps or drain cocks connected to it. But this need not be too inconvenient if you make up the complete branch line before you turn the water off so you are without water only while you make the final branch connection.

Connecting into lead pipe

Inserting a tee junction into lead pipe involves joining the run of the tee into two ‘wiped’ soldered joints Join short lengths of new copper pipe into opposite ends of a compression tee. Measure the length of this assembly, and cut out 25mm (1 in) less of lead pipe. Join the assembly in with wiped soldered joints – a job that takes a lot of practice, and one you may prefer to leave to a professional plumber until you have acquired the skill. You then connect the branch pipe to the third leg of the tee

Connecting into iron

Existing iron pipework will be at least 25 years old, and likely to be showing signs of corrosion. Extending such a system is not advisable – you would have difficulty connecting into it, and any extension would have to be in stainless steel. The best course is to replace the piping completely with new copper piping.

Connecting into polythene pipe

If you have to fit a branch into a polythene pipe it’s not a difficult job, especially if you use the same material. Polythene pipes are joined by compression fittings similar to those used for copper. Polythene hasn’t yet been metricated in the UK and each nominal pipe size has a larger outside diameter than its copper equivalent. So you’ll have to use either special gunmetal fittings for polythene pipe (still made to imperial sizes) or else an ordinary metric brass fitting a size larger than the pipe – 22mm for 1/2in polythene.

You also need to slip a special metal liner inside the end of the pipe before assembling each joint to prevent the pipe from collapsing as the cap-nuts are tightened. In addition, polythene rings are used instead of metal olives in brass fittings. Apart from these points, however, inserting a tee in a length of polythene pipework follows the same sequence as inserting one into copper.

Connecting into UPVC pipe

As with polythene it’s an easy job to cut in a solvent weld tee – a simple collar fitting over the ends of the pipe and the branch After you’ve cut the pipe run with a hacksaw you have to roughen the outsides of the cut ends and the insides of the tee sockets with abrasive paper and then clean the surfaces with a spirit cleaner and degreaser. Solvent weld cement is smeared on the pipe ends and the insides of the sockets, and the pipe ends are then ‘sprung’ into the sockets.

You have to work quickly as the solvent begins the welding action as soon as the pipes meet. Wipe surplus cement off immediately, and hold the joint securely for 15 seconds. After this you can fit your branch pipe to the outlet of the tee.


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