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Water Pipe and Plumbing

Selecting and using water pipe

Water pipes have been made from lead copper steel and PVC. Here we look at the evolution of plumbing pipe and the PVC pipe in modern everyday use, the fittings we use and how we join it. We also look at poor installation problems and good practice of how to install PVC pipe.

Lead Water Pipes

Romans were plumbers, early Roman water pipes were made from lead. The word plumbum is, in fact, what the Romans called lead and hence our word plumbing.

Lead pipes were used for water supply right up until the 20th century and it is highly likely that the lead killed a few people over the years. In Britain even now there are still many old houses that have lead pipes in their plumbing systems.

The old lead pipes had a major problem in that they had to be soldered to join them together. Soldering lead pipes is not easy and a specialist skill, a matter of trying to get the stuff into the right place and a lot of wiping the excess away.

Galvanised steel water pipe

With the advent of galvanised steel pipes pipe fittings such as elbows and tee pieces were introduced. Joints were relatively easy using tapered screw pipe threads although it did take a long time to cut through a pipe with a hacksaw. You also need special equipment to cut the thread. Joints were originally sealed using waxed string and, later, plumbers tape.

Steel pipe is still used for certain purposes and there are still tradesmen around who can install and maintain it. It is galvanised on the outside to prevent rusting but they do suffer from internal rusting and eventual failure.

Copper Water Pipes

In the mid 20th century copper became the metal of choice for household plumbing systems and were joined either using brass ‘compression’ fittings or soldered copper fittings. Compression fittings are made from brass and have screw on compression nuts which grip the pipe and seal it onto a ring called a ferrule. These days copper pipe is used in air conditioning systems but, owing to cost, not generally in water supply systems.

PVC Water Pipes

Copper became very expensive and plastics technology came up with alternatives. These days the most widely used pipe for household plumbing is made from PVC (polyvinyl chloride). This pipe is not suitable for hot water and we’ll come to that later. PVC is strong, rigid, doesn’t rust or deteriorate, is chemical resistant, can take pressure and is low cost. In addition it is easy to melt and form into whatever shape is required. The PVC is usually grey in colour and has pigments added to protect it from damage caused by the ultraviolet light in sunlight.

If you see a piece of plastic pipe that has faded to white this is the result of damage from the sun and you will find the plastic has broken down and can become quite brittle and may crack easily. Even though PVC pipe has protective pigments in the polymer it is a good idea to apply a coat of paint if the pipe is to be exposed to the sun.

PVC Pipe Fittings

Fittings for PVC pipe include sleeves for joining two straight pieces of pipe together, elbows for putting 90 degree or 45 degree bends in a pipe, tee pieces for taking a pipe off a straight length of pipe, reducers for connecting large diameter pipe to smaller diameter of pipe and threaded end fittings to allow you to screw a tap, pump or other item on to the end of a pipe.

Fittings and pipe come in a range of sizes usually from 12 millimetre or half inch up to 150 millimetre or 6 inch. For home use smaller sizes tend to be used for water supply while the larger sizes are used more for drains and gutter downpipes.

You can also get plastic stop valves for use with plastic pipe and if you take a look in a pool pump room you are almost bound to find one or two.

Selecting PVC Pipe

When selecting PVC pipe we need to consider the quality and thickness of the pipe. Remember that for water supply the pipe will be pressurised. If you want to get water to that shower of the third floor then you will need a pump to pump the water up to pressure to get it up there and then some more pressure to squirt it at your naughty bits and help to get the deposits off your skin.

The need to carry pressure can be challenging. The pipe and fittings need to be thick enough to resist the pressure and, of course, the joints between the pipe and the fittings need to be good enough to take the pressure also. If your pump is sucking water up from a bore the pipe must have the strength to resist suction which is trying to flatten the pipe.

Good quality pipe has a wall thickness sufficient to take pressure. Your local ‘plumber’ whose technical knowledge came from reading Superman comics may well save a bit of money by buying low cost thin wall pipe, a common cause of plumbing disasters.

Selecting pipe fittings

Next the fittings and the pipe need to fit snugly together so the manufacturing tolerances need to be accurate both in the pipe and the fittings.

The fittings have a “socket”, a sleeve into which the pipe is installed, this socket needs to be deep enough to give good strength and sufficient surface area in the joint to ensure a good adhesion. Low cost fittings tend to have short sockets to save a bit of money on the plastic

Finally the PVC needs to be well formulated so it is dense, not too brittle and needs to be “uPVC” (unplasticised PVC) to make it rigid.

It is best to use branded high quality pipe and fittings. Wavin is good and so is Rucika, Maspion make good pipe but the fittings tend to have short sockets.

These days even toddlers in their cots can install plumbing. All you need is a bit of pipe, a few fittings, a hacksaw, sandpaper and some solvent cement. Even so it is surprising how often ‘plumbers’ with dubious skills can manage to fail.

Why Do We Get Leaks in PVC Water Pipes?

It is very common to find leaks in the pipework of new buildings. You have a brand new villa and you find the water pump is running endlessly or the PDAM water metre is spinning very quickly. You have a leak in your pipes. The whole house is concrete and tiles. Eventually the leak is tracked down to somewhere behind that wall beautifully finished in rare green veined Italian marble. There is no option but to cut the expensive marble only to find that the plumber used glue instead of solvent cement or forgot to glue the joint at all.

When they are installing pipework plumbers tend to cut the pipe and assemble it together and then go along afterwards to glue the joints. It is very easy for the plumber to be distracted and miss a joint and not check afterwards. You might not find out until the bathroom (and any other room for that matter) is finished and the water gets turned on.

Even more common is the use of glue rather than solvent cement. There is very little difference in the appearance of the two but there is a large difference in the final effect.

Use PVC solvent cement not glue

Glue sticks the PVC together whereas solvent cement melts the PVC and so effectively welds it together. The surface of PVC is as slippery as a frog’s buttocks and so glue doesn’t stick very well and, once the pipe is full of water under pressure, the joints may well blow apart.

How to join PVC pipes

Making a good joint in PVC pipe is not difficult - you find a good plumber to do it for you. It’s a good idea to test him first, put a piece of PVC pipe into his hands, if his eyes glaze over or he looks at the pipe with awe it is probably best to find another plumber.

Plumbing these days is not difficult and if one armed nuns can make a fist of it so can you. First cut the pipe to length with a hacksaw, use the sandpaper to tidy up the cut end of the pipe then assemble the joint to make sure the pipe and the socket it is to go into fit together properly and that the pipe is going in the direction you want. As I said before plumbers tend to assemble a whole length of piping and when they are happy with its position they go back and glue it. When you are happy your joint is alright you can join it.

Clean the pipe using PVC solvent (try not to get it on your hands as it is nasty stuff and has a tendency to interfere with your genes). PVC solvent may be difficult to buy in which case use a very fine sandpaper to clean and take off the surface of the PVC pipe. Coat the two surfaces to be joined (the end of the pipe and the inside of the socket) with PVC solvent cement (not glue) then push the joint together into its final position.

As I said earlier PVC is not suitable for hot water and we’ll talk about that another time.

Copyright © Phil Wilson March 2013
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