Module 2: Identifying Drainage Pipe materials, jointing, drainage furniture

Trainer note:

We need to understand the principals of drainage construction, as without this knowledge we are unable to assess faults and determine their cause, this is also true when recommending the best form of repair.

( Discuss the picture with the group and the different drainage systems shown and drainage furniture prior to going through them in more detail.

There are various forms of pipe materials all with specific characteristics, and understanding these is essential. The next section will show the basic workings of drainage including all of the fittings, accessories and terminology used, which maybe encountered on a daily basis.

Trainer note:

Clay pipes are generally mass produced selected clay is ground to a fine powder and a sufficient amount of water is added during moulding, once moulded they are placed in a kiln for drying.

There are over 250 fittings, such as bends, junctions, channels, gullies and traps available.

The advantages of clay pipe are that the short lengths of pipe and wide variety of fittings are adaptable for both simple and complicated drainage systems.

The disadvantages to clay pipe are that it is heavy in weight, easily damaged whilst handling and can be difficult to cut.

Trainer note:

Rigid Jointing - This method comprises of a gaskin of hemp dipped in tar that is rammed between the spigot end of one pipe and the socket end of another. This is then sealed with sand and cement to form a rigid joint.

Trainer note:

This pipe material was first used in the UK some 50 years ago and is now extensively used because of its ease of handling, cutting, jointing and relatively low cost. The pipe is light in weight, flexible and to some extent can deform under pressure without fracturing. As the pipe is produced in long lengths consequently fewer joints are needed which makes laying the pipe relatively quick.

Trainer note:

Flexible Socket Joint - The flexible socket joint that is made of rubber comprises of a plastic fairing cast on the spigot and socket end of the pipe.

Flexible Coupling Joint/Band Seal - Made with a close fitting, flexible plastic sleeve with rubber sealing rings. The plain ended pipes are bevelled to assist in forcing pipe ends into the sleeve to make a close watertight seal.

We can see how the band seals are used to connect plastic to clay.

Trainer note:

For over a hundred years cast iron pipes have been used for drains underground. A cast iron pipe is brittle or rigid and may suffer fractures under heavy loads or due to careless handing.

Cast iron pipes are used for drains due to their superior strength were there is unstable or made up ground, in shallow trenches, under buildings, in heavy water logged ground or were sewerage is under pressure from pumping.

Trainer note:

They were mainly used during the 1950’s & 1960’s and have no longer been manufactured since 1972. They were made of wood cellulose fibre (approx. 25%), impregnated with coal tar pitch (approx. 75%), under pressure. The pipe lengths varied but were typically 2.5 – 3.0m.

Trainer note:

Why Were They Used?

They were more flexible than the traditional vitrified clay alternative, which had rigid cement joints. So they were often used in locations where ground was liable to uneven settlement.

They could be laid at lower gradients than some other materials.

They were available in lightweight and longer lengths that were quicker and easier to lay, with less wastage.

More significantly, there are a large number of installations where exhibiting differing degrees of distortion. This was generally characterised by the squashing or flattening of the pipe (generally the height decreased and the width increased). Again, this was thought to be due to the premature failure of the pipe material, leading to the loss of structural integrity. The pipes were therefore unable to withstand the loads imposed by the ground or whatever was above them. The distortions in the pipe also resulted in distortion and failure of the joints. This, in turn, allowed water to leak from the joints and erode the support from under the surrounding pipes, leading to further stresses, movement and damage.

It is now widely accepted that although Pitch Fibre Pipes complied with all relevant regulations when they were installed, they are unsuitable for use underground. They have a limited useful life of between 25 and 50 years, depending on many factors, such as the quality of installation and the ground conditions. Many show clear signs of delaminating or distortion after 30 years.

Trainer note:

Drainage has to be set at the right gradiant.

Too much fall and the water runs away too fast leaving the solids behind resulting in a blockage

Too shallow a depth and the water doesn’t move the solids in the drain resulting in a blockage.

Rule of thumb was 1:40 fall for 4inch and 1:60 for 6 inch.

Trainer note:

Drop Shafts – Are near vertical pipes that are installed when the depth of the drain has to greatly increase to gain the correct level into the main sewer. Because drop shafts are near vertical pipes they are, by design, susceptible to ground movement and fractures to the pipes are regularly noted.

The term backdrop shaft maybe used; this is usually where the drop shaft is located close to (and runs into) an inspection chamber/manhole as the illustration shows.

Trainer note:

Inspection Chamber/Manhole A small covered shallow chamber that allows access to a drain or sewer and is usually situated within the boundary of the property. Inspection chambers/manholes give access to clean out the drain system and are ideal for allowing access for CCTV inspections. Inspection chambers/manholes can be made of plastic, brick or concrete rings and are usually maintained by whoever is responsible for the outlet pipe.

Trainer note:

Interceptor Trap showing the rodding eye and the trap underneath where the water and solids flow through. These are usually situated in the last Manhole before leaving the boundary. They carry out 3 purposes. 1. Create a barrier between the main and the domestic drain to prevent build up of gasses 2. Prevent vermin 3. catch debri to prevent the main getting blocked

Discuss stand alone interceptors

Stop smells

Prevent vermin

Catch debri

Trainer note:

Pumping Chamber - If the main sewer is accessible but at a higher level than the domestic foul drain then a Pumping Chamber may be used to pump unsettled sewage directly to the mains. Drainage from the house is fed by gravity into the pumping chamber, which is normally situated on the property

Trainer note:

Gully – is a small chamber where waters are “trapped” before they are allowed to flow into the drainage system. The trapped water prevents smells/rats from coming back up the drain. By their design gullies can regularly block, as they will hold an amount silt/waste material in the “trap” of the gully. Regular maintenance checks should be made to gullies and any silts/waste materials held in the gully should be removed. Kitchen gullies regularly block as the fats and greases introduced from kitchen sinks and utility items congeal in the piping downstream of the gully causing blockages to occur.

Prevent smellw

Stop vermin

Catch debries

Trainer note:

Is the above ground vertical cast-iron or plastic pipe that usually takes waste away from the toilet and bathroom. The SVP ventilates the drain and is commonly fixed to the exterior of the building however SVP’s can also be found inside the house and this is classed as an internal SVP.

( Discuss with group how everything has a trap on it to prevent smells)

Trainer note:

Rest-Bend – The usual location of a rest bend is just below ground level and it is the connection between the (vertical) SVP and the (near horizontal) underground drain. Rest-bends are normally manufactured to 90°.

Trainer note:

Rain Water Down Pipe - This term is used for the sections of pipe that link roof gutters to underground drains. They can feed into gullies or run directly into the ground with no specific access.

( Discuss with group access issues for carrying out a CCTV)

Trainer note:

Catch Pit Manholes - A catch-pit manhole should be considered preceding any outfall to a natural watercourse, to remove grits, silts and excess sediment. A catch-pit is, essentially, an empty chamber with an inlet pipe and an outlet pipe set at a level above the floor of the pit. Any sediment carried by the system settles out whilst in the catch pit, from where it can be periodically pumped out or removed.

Trainer note:

Culvert – The definition of a culvert is that it is a conduit for a watercourse. Land drains, streams, rivers etc. can be culverted and these culverts are usually found under roads, fields or underground where houses have been built close to a watercourse. Culverts are not usually covered under the terms of a domestic buildings policy, as in land drains.

The law states that in most cases land drains and culverts are usually the sole responsibility of the owner of the land through which the conduit passes and this is known as riparian ownership. This means that the owner of the land probably has the sole responsibility to maintain the culvert even though the household drains do not run into the conduit. Culverts are susceptible to blockages as they silt up over time and as such it would be good advice to refer the land owner to the Local Authority to ask them for advice as to the status of ownership of the culvert.

Trainer note:

Land Drains – Land drains can be found anywhere throughout the country, typically where houses are built in areas where high water tables or marsh ground exists. A land drain encourages water from the surrounding strata into the pipes by means of small holes that are made in the clay/plastic pipes during manufacture. Another method to drain waters away is to butt clay pipes together, the joints in this type of system are never sealed and indeed surrounding waters enter these pipes at these opened butted joints. Land drains are not usually covered under the terms of a domestic buildings policy as they do not actually serve the house – they are positioned to drain the localised land, which they run through. It is usual for policy wording to state that cover will apply for “accidental damage to underground pipes ad cables, which serve the home”. Home is recognised as including the house and outbuildings only.

It is important to note that if a surface water system from the house or outbuilding is connected into a land drain then cover may apply, downstream of the surface water connection. In practice this is very rarely found, as it is usual for the waters from a land drain to feed into a watercourse such as a stream, river, lake and very often a culvert.

Trainer note:

Rodding Eye – A small access point usually found at the upstream end of the drain or sewer formed by bringing the end of the pipeline to the surface of the ground. The opening is usually on larger than the diameter of the pipe and is usually blanked off with an access cover. Rodding eyes can also be found at the base of the SVP and will give access to a drain or sewer for drain rods and CCTV inspections.

Trainer note:

Non- Return Valve - Non-Return valves are used when there is a risk of a main sewer reaching its full capacity and sur-charging up branch connections, causing flooding to properties. The non-return valve opens only one way, releasing fluids from the connecting property but preventing fluids from entering the private system from the fully charged main sewer. The only draw back is when the main sewer is fully charged and the valve is closed the fluids from the private property have only a limited amount of storage capacity and can cause sur-charging.

Trainer note:

usual usage is for surface water runoff from roofs/gutters. Where the waters go to ground pipes may take the waters away from the property and into a soak-away where the waters percolate into the sub-soils. A soak-away are usually pits filled with pea gravel/stone chippings and over time they gradually become clogged with debris, detritus material and/or silts

A percolation test is required if the soakaway is to be moved to a new location

Trainer note:

Pictures showing a typical soakaway. One using pea gravel and one using crate system

Trainer note:

A percolation test is a test to determine the water absorption rate of soil in preparation for the installatioin of a soakaway or drainage field

Trainer note:

A percolation test is a test to determine the water absorption rate of soil in preparation for the installatioin of a soakaway or drainage field

Trainer note:

General binding rules: small sewage discharge to the ground

New rules came into force on 1 January 2015. If your system was installed and discharging before 31 December 2014 you have an ‘existing discharge’. If your system was installed and discharging on or after 1 January 2015 you have a ‘new discharge’

Rules for existing and new discharges

Use the correct treatment system

You must use a septic tank or small sewage treatment plant to treat the sewage and then discharge the effluent (treated liquid) to ground via a drainage field.

A septic tank is an underground tank where the solids sink to the bottom, forming a sludge, and the liquid flows out to a drainage field.

A small sewage treatment plant, also known as a package treatment plant, works in a similar way to a septic tank but uses mechanical parts to treat the liquid to a higher standard before it goes to a drainage field.

A drainage field, also known as an infiltration system, is a series of pipes with holes placed in trenches and arranged so that the effluent can trickle through the ground for further treatment.

You cannot use a soakaway (designed for draining rainwater), well or borehole for discharging effluent to ground. Instead you must either upgrade to a drainage field or apply for a permit so that the Environment Agency can assess the risk of using this sort of system in your location.

Trainer note:

Septic tanks come in many shapes and sizes. Traditional systems were constructed of brick or concrete and could be comprised of single or multiple chamber systems. The inlet pipes and outlet pipes to the various chambers are known as “DIP PIPES” .

Doubled dip pipes connecting through an internal baffle wall are known as “H”pipes.

Trainer note:

Dip Pipes & H Pipes In Septic Tanks

These are placed within the external and internal dividing walls of a chamber to isolate the solids and waste matter. They are designed to allow water to freely move through the system, they are no great mystery and are easily constructed out of standard bends and square (90 degree T) junctions. The base of the dip pipes and H pipes re extended down towards the base of the chamber so that the deeper sediment free waste water is able to pass up through the pipe and into the next stage of the system.

Trainer note:

From low profile tanks to Onion shaped Klargesters there are many types of tanks.

Trainer note:

Modern tanks constructed from fibre glass and plastics work in much the same way as the older systems as the image to the right shows, the central baffles divide the tank into three sections whilst allowing waste water to move through the system.

The inlet pipe discharges directly into section (a) where some solids float and others settle, clarified effluent passes up through the slotted baffle into area (b) where finer particles of scum and waste are again separated before the waste water passes into section (c) and into the outlet pipe work.

The central ball rises to the top of section (a) forming a seal when the tank initially fills, when the tank is emptied the ball lowers allowing access to the sludge at the bottom of section (a)

Trainer note:

Picture of a septic tank with a herringbone soakaway system.

( Discuss with group difficulties with access to CCTV )

Trainer note:

Discuss with group the t pipes and the what they do and how they work include H pipes though not on this picture. Typical ways they get damaged.

Trainer note:

A cesspit is a covered watertight tank that is used for receiving and storing sewerage. Having no outlet a cesspool should be regarded as a holding tank and should be emptied before it fills.

British Standards dictate that the minimum capacity of a cesspool should be 18 cubic meters – this should last the average household at least 45 days.

Trainer note:

1. Primary Settlement Tank

Wastewater and sewage flows into the primary settlement tank

where the large solids are retained for future removal.

2. First Stage Biological Treatment

The liquor and fine solids then flow into the Biological Treatment

Zone 1 where the first stage of treatment occurs.

3. Second Stage Biological Treatment

The liquor is then fed forward at a controlled rate into Biological

Treatment Zone 2 for further cleaning.

4. Final Settlement Tank

The clean liquid passes into the final settlement tank where it

can be discharged to ground or water course.

Trainer note:

Onion style tank strapped down and requires concrete

Low profile tank requires shingle surround