Requirements for Cold WaterStorage Cisterns

A presentationbyDouglas WebleyandDebra Taylor-Croather

Requirements for Cold Water Storage Cisterns

Introduction

The aims of this slideshow are to: •Introduce the regulations for the installation of cold water cisterns

The objectives of this content are to ensure that students are aware of:

•The general requirements for storage cisterns•The installation requirements for storage cisterns•The Requirements for Positioning Storage Cisterns•Water inlet requirements for storage cisterns•Water outlet requirements for storage cisterns•Warning and overflow requirements for storage cisterns•Requirements for coupling storage cisterns•Commissioning storage cisterns

The general requirements for storage cisterns

When it is required to store cold water for use as a supply for an indirect system of cold water, or for the feed to a system of dhw, the water is stored in a cistern, usually in the loft space.

The cistern should have a close fitting lid that prevents any light or insects from entering the cistern but it must not be air tight. To ensure of this all vents, warning pipes and overflows should be screened with a corrosion resistant mesh with a maximum opening size of 0.65 millimeters.

An access cover should be provided if the tank volume is greater than 1000 litres. This is to ensure that maintenance and cleansing can be performed without completely removing the cistern cover.

The general requirements for storage cisterns

Some of the possible consequences of not following the general requirements as set out in regulation 16 are that the water stored can become contaminated by; insects that gain access via the open lid or by crawling up the unscreened warning or overflow pipe, insect larva that require water to complete their lifecycle such as mosquitoes.

Animal waste from birds or rodents that can access the area around the storage cistern, the bodies of birds or rodents that have got trapped in the cistern and died.

The above diagram shows a correctly installed water storage cistern

Any of the above problems can cause contamination of the water supply and are a potential health hazard to those using the water supplied from the cistern.

The general requirements for storage cisterns

The storage cistern should have a minimum capacity of 100 litres. If the cistern is also to act as a feed cistern for a hot water supply, it must have a minimum capacity of 230 litres.

If the cistern is also to act as a feed cistern for a hot water supply it should have a minimum capacity of 230 litres.

For more information on the general requirements see section G16.13 of the Water Regulations Guide.

The installation requirements for storage cisterns

The storage cistern would need to be adequately supported to prevent distortion or damage to the cistern and pipe work. Water is very heavy,1 Litre weights 1kg. 1 cubic Metre weighs 1000 kg. From this we can appreciate that the support for the cistern would have to be substantial. Normally we would try and position the base for the cistern over a load bearing wall in the roof space.

The installation requirements for storage cisterns

Insulation is not included beneath the cistern and if it is present at installation should be removed.

For domestic installations the support for the cistern will be made of moisture resistant close boards covering the total area of the base of the cistern.

The close board is fully supported across the width with three pieces of wood measuring at least seventy five Millimetres by fifty Millimetres that are no further apart than three hundred and fifty Millimetres.

All holes made in a plastic cisterns should be made with a hole saw. It is essential that you remove any plastic that may fall inside the tank during any cutting operations performed on the cistern.

The Requirements for Positioning Storage Cisterns

The requirements for the positioning of and access to cisterns depend on the volume of the cistern involved.

Positioning cisterns of 1000 litres and below

The Requirements for Positioning Storage Cisterns

The requirements for the positioning of and access to cisterns depend on the volume of the cistern involved.

Positioning cisterns of 1000 litres and above

For more information on the positioning requirements see section G16.14 of the Water Regulations Guide.

Water inlet requirements for storage cisterns

The inlet requirements state that all cisterns will be fitted with an adjustable water inlet control device.

These devices are usually float operated and must conform to British Standard 1212.

Float Valves

The British Standard defines four types of float operated valves that are suitable for use in cold water cisterns:

•Part one - Portsmouth type •Part two - Brass Diaphragm type•Part three - Plastic Diaphragm type•Part four - Diaphragm Equilibrium type

Water inlet requirements for storage cisterns

The diagram below shows a cross section of a common float valve. The diaphragm indicated can be made of brass (BS1212 Part 2) or plastic (BS1212 Part 3).The adjustment screw allows for the valve to set at the correct water level.

It is important to note that British Standard 1212 only covers valves up to 2 inches in size. Any float valve fitted that exceeds this size must authorised by one of the following bodies:

1 - Water Regulations Advisory Service2 - Water Fittings and Materials Directory3 - Your Local Water Provider

For more information on inlets to cisterns see section G16.4 of the Water Regulations Guide.

Water outlet requirements for storage cisterns

Outlets from cistern include indirect cold water feeds, cold supply to hot water systems such as immersion heaters and central heating systems.The diagram shows the positioning of cold water distribution and hot water system feed pipes. It is recommended that the cold water feed pipe be taken from the bottom of the cistern. This is to prevent the build up of sediment on the bottom of the tank alternatively the cold water feed can be located on the side of the cistern.

The distance between the cold water feed outlet and the hot water system feed, indicated by arrows A and B on the diagram, should be not less than the internal diameter of the outlet pipe being used.

Hot water system feed pipes must always be positioned above cold

water system feed pipe.

Water outlet requirements for storage cisterns

Prevention of Stagnation

Correctly positioned outlet pipes can help to prevent stagnation of the water held in a cistern by ensuring a through flow of water.

If there is only one outlet fitted then it must be positioned on the opposite side of the cistern to the water inlet valve.

If there are two outlets fitted they should be positioned on opposite sides of the cistern with one higher than the other . The higher outlet should be on the opposite side of the cistern from the water inlet valve. This arrangement ensures circulation of the water within the cistern which in turn helps to prevent stagnation..

Warning and overflow requirements for storage cisterns

Cisterns Under Five Thousand Litres

A warning pipe has a smaller diameter than an overflow pipe and is intended to act as a warning of imminent overflow.An overflow pipe has a larger diameter than a warning pipe and should be able to carry the excess water that would be present if the inlet valve fails completely and lets in the maximum amount of water possible. This should ensure that the inlet valve will never become submerged and the cistern will not flood the area in which it is situated.Warning and overflow pipes should run to a point outside of the building that is clearly visible and below the level of the storage cistern. Warning pipes should be situated below the overflow pipe so it is obvious which pipe is which. Overflow and warning outlet requirements for cold water cisterns vary with the storage volume of the cistern being installed .

Warning and Overflow requirements for storage cisterns

Cisterns Below 1000 litres

Cisterns below one thousand litres capacity require a single combined warning and overflow pipe. The bottom of the combined warning and overflow pipe should be a minimum of twenty five Millimetres above the water level of the cistern.

Warning and Overflow requirements for storage cisterns

Cisterns above 1000 litres and below 5000 litres

Cisterns above one thousand litres capacity require separate warning and overflow pipes.

The bottom of the warning pipe should be a minimum of twenty five Millimetres above the water level of the cistern.

The bottom of the overflow pipe should be a minimum of twenty five Millimetres above the bottom of the warning pipe.

For more information on warning and overflow pipes see section G16.8 of the Water Regulations Guide.

Warning and Overflow requirements for storage cisterns

Cisterns Over Five Thousand Litres

Cold water storage cisterns with a volume greater than five thousand litres require warning systems that indicate when problems develop.Cisterns above five thousand and below ten thousand litres capacity require a single overflow pipe.

The bottom of the overflow pipe should be a minimum of fifty Millimetres above the water level. Cisterns of this capacity should also be fitted with a visual water level indicator. This system should have a sensor that is mounted twenty five Millimetres above the maximum water level of the cistern.

Warning and Overflow requirements for storage cisterns

Cisterns Over Ten Thousand Litres

Cisterns above ten thousand litres capacity also require a single overflow pipe. The bottom of the overflow pipe should be a minimum of fifty Millimetres above the water level. Cisterns of this capacity should also be fitted with a visual or audible alarm.

This system should have a sensor that activates the alarm when the water comes within fifty Millimetres of the bottom of the overflow pipe.

For more information on warning and overflow pipes see section G16.8 of the Water Regulations Guide.

Requirements for Coupling Storage Cisterns

It is sometimes desirable to couple two storage cisterns together rather than have one large storage cistern. This can happen in larger scale installations or where a lack of space limits the size of cistern that can be used and there is a need for storing a larger volume of cold water than one small cistern could hold.

Another benefit of using two coupled cisterns is that maintenance can be carried out on one cistern without having to interrupt the water supply to the rest of the system.

Requirements for Coupling Storage Cisterns

The diagram above shows two cisterns coupled in such a way that either could be isolated from the other. This arrangement is not usual in domestic situations.

The diagram shows the more common coupling arrangement found in domestic dwellings where coupled cisterns have the water inlet in one cistern and the water outlet taken from the other. This is to aid water circulation and prevent the possibility of stagnation.

Commissioning Cold Water Storage Cisterns

Once the installation of a cold water storage tank is complete the system must be commissioned before being cleared for usage.Often not enough time is allocated for this task or it gets overlooked completely but it is important to ensure that the job has been finished and that there are no loose connections or anything else that could cause problems. Water can cause major damage that is expensive to correct. Before commissioning cisterns should go through the following checks:

Visual Inspection

Check the cistern visually, is the inlet valve fitted, are the outlet pipes fitted, are the warning and / or overflow pipes connected correctly, is the cistern situated correctly, does it have adequate support, is the lid fitted correctly, are the air vents, warning and overflow pipes screened to prevent insects gaining entry to the cistern, if it is a large cistern is there a warning gauge or alarm fitted, is the cistern sufficiently insulated.

Commissioning Cold Water Storage Cisterns

Soundness Testing

Check that all connections to the cistern; water inlet and outlets, warning and overflow pipes have been tightened and are watertight.Check that any joints in the pipe work to and from the cistern are water tight and that the pipes are insulated.

Flushing and Disinfecting

When ever any work is carried out on water supply systems the apparatus and pipe work involved should be flushed and disinfected in accordance with British Standard 6700 clause 3.1.10.1For small installations, a single dwelling for example, a visual inspection and removal of any debris from the cistern and flushing of the pipe work with clean water to remove any flux remaining in the pipes would be sufficient. For blocks of flats and larger buildings then full disinfection as described in British Standard 6700 would be required

Commissioning Cold Water Storage Cisterns

Performance Testing

It is important to ensure that the cistern can meeting the demands that will placed upon it. To these ends the cistern should be tested to full capacity to ensure that there is no individual system that gets starved of water when demand on the cistern is at is highest. This is important because if hot water systems do not get sufficient water then scalding can occur due to the water getting over heated.

Final Checks and Handover

Once the above tests have been completed it is a good idea to give the system one last check over to see if any problems have come to light during the tests.

You should now be confident to hand over the installation to the customer.

Acknowledgements

Written and produced at South Birmingham College

The Centre for the Built Environment

Textual content written by Douglas Welby and Debra Taylor-Croather with additional content by Christopher Poole

E-Learning Content Development Unit

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All drawings by Christopher Poole

Distribution

Distributed by the Learning and Skills Development Agency and the National Learning Network as part of Project Q 2005

Important InformationPlease Note

While every attempt has been made to ensure that the contents of this learning object are correct and follow the guidelines as laid down in the Water Regulations Guide second edition South Birmingham College cannot be held responsible for any loss or damage caused by reliance on these materials. All works should carried out by fully qualified persons.