Duct Protection

There are many cases where the duct needs another layer of comfort. This may be for -

Aggressive ground conditions - rocks, stones
Strength to withstand weight from above such as a wall, or traffic
Strength to withstand river flow
Strength to withstand attack from above, such as fence posts and tent pegs, cow legs even
Strength for bridging
Protection from light

An outer duct is sometimes used as a conduit, put in place so that the orange ducts can be passed through at a later stage. this may involve using a drawstring to pull the inner duct through.

This comes down to some sort of steel or some sort of polyethylene. Steel is difficult to bend but clearly stronger. Polyethylene can be Medium Density (MDPE) sometimes called Alkathene or High Density (HDPE).

The usual weapons of choice are steel scaffold tube and alkathene water pipe in 25mm, 32mm, 40mm or 50mm diameters. And don't forget that if you used multi-core that comes with its own extra layer already.

They can be used in combination as well. Use short lengths of alkathene at each end of a scaffold pipe to get a curved exit. Use a metal collar to a continuous alkathene pipe to add mass in the middle of a stream.

Other useful possibilities are the selection of stuff that you will find in any farmyard - a wide variety of pipes that 'might come in one day'

There is also a need for clip-on ducting for protecting small sections of duct that have already been laid. Okay you could cut and join it (probably using 2 joints) but that would be less satisfactory and more expensive. There could also be the case where your duct has already got fibre in it.

There is also a need for some sort of metal shield above the duct to protect from fence posts and such-like, it doesn't need a whole tube. But this may be more expensive than the more mass produced scaffold pole.

Outer Duct

We used a fair bit of 25mm, 32mm and 40mm black alkathene ducting as outer protection. The smaller the diameter the easier it is to lay it, but the harder it might be to feed the orange ducts through it. Keep some samples of each size so that you can assess what size outer to use for a certain bunch of orange ducts. Feeding through 1 metre of outer duct is a lot easier than through 20 metres which is a lot easier than 100 metres. We always erred on the side of having our outer duct too small and spent a lot of time pushing.

Too large a duct means there is a risk of mice being able to travel down the duct and nibbling the duct and fibre.

It pushes through a lot easier the more you manage to straighten out the outer duct. Flapping the outer duct helps.

In some cases, you will want to bury the outer and feed the orange through later, sometimes you will pre-load the outer with the orange before you bury it. If you do the former then any deformation of the outer by rocks will make it harder to push the orange through. But if it feeds easily then you know that the inner duct is undamaged.

Never tried it, but it would be possible to moleplough a 16mm with a 7mm preloaded inside it. Can't quite think when you might want to do that, but someone will have a situation where this is the answer.

The 40mm outer duct has a thinner wall than the others, it is still strong, but kinks easier.

There is now purple outer ducting available. We have no experience with it yet. At first glance it looks useful but bulky and not super-strong, and a bit like mouse tunnels. It seems to get laid before it is threaded with orange ducts, which means a drawstring has to be arranged in the tube. Ends of the drawstring are held in place by tying these ends to an offcut of purple duct.

There is now the 18mm black duct available. Same internal diameter as the 16mm but a lot stronger and okay in daylight. This is really useful in the right circumstances. (You might have trouble getting B4RN to give you some, but if you have a specific job in mind for it then you’ll get some.)

Mouse damage. Use fibre-glass roof insulation to stuff in any gaps in the ends of outer ducting.

Black 18mm duct.

It is not clear how news of innovative items such as the purple outer ducting gets spread out to existing village projects. We have recently got hold of a drum of 18mm black ducting from B4RN. We heard about it by chance.

It is really useful stuff. It is the same diameter as the 16mm orange internally, but it is a lot stronger and okay in light. There are lots of occasions where you would just like a stronger duct, so in the past we would thread the 16mm through some 25mm water pipe, but now you have the option of the black 18mm duct. Ideal for some heavy traffic areas or areas where you can't get so deep. Easy to work with, you can moleplough it if necessary.

The only drawback is that it cannot be easily joined to 16mm - Bruce at B4RN has invented what they call the "pencil sharpener" which shaves down the 18 to 16 so that the usual connector works. (18X18 connectors exist, but are also closely guarded - you have to convince Nick of your competence before you can get hold of them)

These look like perfect cases for 18mm black duct. These are all cases where it's not going to be very deep, and it could do to be a bit stronger but without the extra bulk and inconvenience of a larger outer duct.

The extra protection where the duct enters is good. It should be standard practice.

And the rim hasn't been screwed on yet

Alkathene

Standard water pipe. Also in black.

Easily available, relatively cheap.

An excellent example from B4RN 4 Halton

Joints are off-set. Joints are cable-tied to the other duct, not quite tightened. The ducts are protecting each other.

And above that, they have sleeved that whole two-metre section in a black outer-duct.

Typical example.

This section of pathways has been re-modelled with a handy duct installed. It has been concreted over. This has been prepared a while ago, with the duct being passed through later.

This middle section is crying out for an extra collar as a sleeve over the red outer ducts. It acts as a strengthener to that section - as it is, the 16mm will be pressing slightly over the rim of the 25mm. A one foot section of 32mm could be slid to one side while the 16mm is made and then slid back over the whole section.

METAL

For strength across streams

In generally flat country you can bury a lot of pole either side of the stream. If you get that only as level as the bed of the stream then that is going to be solid, that is going nowhere.

In more rocky areas the stream is more v-shaped and you will not manage to dig down far enough each side. But if you could dig down just one metre either side of the stream low enough then that would work.

METAL

For Bridges

a scaffold pole is 6 metres long. It is strong enough to bridge a 4 metre gap and could be extended slightly further with a metal collar to get to 5 metres.

Beyond that span, the weight of the metal is too great and you need a much more complicated structure.

METAL

Because it is strong and rigid, it doesn't have to be deep. And once in place you can feed ducts through afterwards, it doesn't need to be pre-loaded. (Alkathene is sometimes better preloaded)

Ideal for that scruffy bit, where some will end up exposed. This is over a concrete culvert.

A digger may be able to bend a pipe a little to give you a few more options.

METAL

Because you can hit it. This one doesn't always work. It seems a good idea to be able just to get under a wall by knocking a scaffold pole through. When it works it is often quick and gives a nice strong finish. In practice it often results at best in a very clogged up pipe, and at worst you end up hitting a rock and spend a lot of time shaking a wall.

Not really recommended but people can't resist having a go

The purple ducting that is being used is about £1 a metre for 63 mm duct.

You may be able to get it cheaper than B4RN.

It is supplied with a draw cord already installed. This allows the inner ducts to be pulled through, although it is more like twine which can cut your fingers. You should attach a second cord and it leave it in place afterwards – this will allow you to introduce additional ducts if required at a later date, or if you use a vacuum cleaner you can suck a string through (if you have electricity available)

drawstrings kept from being lost by spare bits of purple

Spare bit of outer duct making a tidying collar.

builders foam used to seal ducts

This is a 16mm orange duct inside what looks like 40mm outer. Wouldn't 25mm water pipe be stronger and cheaper?

Purple duct v Alkathene water pipe - When to use the purple outer ducting

There is a surprising amount of 'that purple ducting' being used.

Purple duct comes in 63mm or 110mm diameters. Waterpipe comes in 20, 25, 32, 50, 63 mm sizes in MDPE. (40mm black pipe is also available but this has a slightly less thick wall.)

Cons

The wall thickness of the purple stuff is about 1mm compared with 3mm for water pipe. It is nowhere near as strong.
The purple stuff is twin wall and each layer is thin. If you hit the outer layer with a hammer, the inner layer splits readily.
The purple stuff is more expensive.
Using an oversized outer-duct introduces the problem of rodent access.
Using an oversized outer-duct makes it more vulnerable to crushing

Rarely will the 63mm purple be preferable to 63mm waterpipe.

Pros

The purple stuff is convenient to work with and comes with a drawstring which can help feeding large bundles of duct.
In cases like under tarmac, where you might prefer to have plenty of space left in the duct so it can be re-threaded, then 110m duct could be useful.
If there are very large bundles of orange ducts then it is a good way of keeping them together
The colour acts as good warning tape.

You ask yourself 2 questions Q1 Do you need outer-ducting at all? Q2 Why is waterpipe unsuitable?

These are all cases where water pipe looks as though it would have had some advantages.

The first two look as though the extra strength would have been good. The 3rd one looks as though a much smaller outer pipe would have been simpler. The last two seem to be be adding bulk for no reason.

Feeding ducts through

You will spend time feeding the ducts

You may have to line up a set of ducts carefully before feeding through an outer duct – for example 3 ducts may have to be organised into a triangle, there may not be enough room for the ducts to twist and turn round each other.

You will need the minimum amount of tape round the ends of the inner ducts, and to offset the ducts by a few inches. In dry conditions you might be able to do it without tape while you get it through. Feeding the ducts through one at a time is usually less successful than all together. (Although it will be the first suggestion you will be offered. Every time.)

Outer ducts sizes fit well inside the slightly larger size. If you had to join a 25 mm tube, you can use a short section of 32 mm as a collar. One of the alkathene sizes also fits neatly into a scaffold pole, so you can use them on the pole at each end to avoid the orange duct rubbing on the metal.

You already know 7mm slides inside 16mm nicely.

Assemble your loom first if really necessary

With a really complicated bundle of ducts you might like to organise them somewhere quieter than where they will end up - particularly true in an urban setting. Once you assemble it, it won't really coil back up very well, it wants to be a long line. So Ingleton just went for a walk into town on a quiet morning and delivered it. They will always remember that day.

And at Silverdale as well

Clip-on duct

There is a need for some sort of clip-on outer duct. You have moleploughed across a field and there are one or two spotty bits where it hit a patch of rocks, in sorting it out you would like to add a foot or two of outer duct. We have been using sections of the outer layer of scrap multi-core ducting, it is fairly easy to slit lengthwise with a Stanley knife and is quite strong but flexible. It can be overlapped round the duct you wish to protect and taped up. We also found some nice heavy-duty outer protection that they use up electricity poles, it is already slit lengthwise. This must be commercially available somewhere. We have also used the foam insulation stuff for lagging pipes where we had a section of stones, this stuff is too expensive to consider sensibly, but it was exactly right for this particular instance.

Clip-on ducting for that short section of ploughing that didn't go too well through a rocky section and just needs a bit of extra protection.

For that short section in your trench that's a bit dodgy.

For that section of orange you can see in a field a few months after you laid it.

For a set of joints that you would like to protect

For that bit where it enters the chamber

Far cheaper than encasing all of a section in outer ducting, just do the bits that need it. Far safer than just backfilling and hoping.

Shop around

How much protection?

You can't always lay the orange duct straight into the ground without some sort of protective layer. This can be because

it is very rocky
you can't get it deep enough
it may be in sunlight
the area is driven over

You kind of have to consider what is best for each situation. You start by knowing what's available - we had never heard of the black 18 mm duct until very late. We would have used it a lot.

You must decide

Are you happy that a section will be deep enough and unlikely to sustain damage?
If not, go up a protection level
If extreme, consider 2 layers of protection (2 layers of outer duct, outer duct + concrete, whatever)

It's really going to have to be a rule of thumb like that, but you might prefer to get someone with experience to look at it.

We got one of our local guys out that did groundworks, but he had had no experience of doing the sort of jobs we were asking him about. He never has to dig through rivers, sling cables under bridges.

B4RN are always busy, and there's only really Nick Hall anyway, so ask your nearest B4RN villages.

Not sure why this needs the purple duct?

Possibly this is a Very Important Section, since it seems to include about five 16mm ducts

25mm black duct would be stronger and cheaper here.

This middle section is crying out for an extra collar as a sleeve over the red outer ducts. It acts as a strengthener to that section - as it is, the 16mm will be pressing slightly over the rim of the 25mm and, as you move it about, is in danger of kinking. It also protects the 16mm join and keeps it on a straighter line. A one foot section of 32mm could be slid to one side while the 16mm is made and then slid back over the whole section.

If no collar is available you can tape a stick across this section to stabilize it. Or a couple of short bits of orange duct as splints.

Wouldn't that be perfect for a scaffold pole? You won't get very deep there , 3 bags of Postcrete and move on. With that plastic stuff you would need about 4 inches of concrete on top and that's a lot of concrete to mix.

This is the impressive Over Kellet lot, there they get up to some high duct bundles (30+). If all the ducts didn't fit in a scaffold pole, then if you laid the extra ones alongside the pole they would still be protected by it.

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