Unit 307 Session 7 Cold water storage cisterns

​Cold water storage cisterns

​In the previous session we learnt about the types of cold water systems, as we could see with both system types there is a possibility that we may need to install a cold water storage cistern. (CWSC).

Open Ended

Do you think the CWSC shown in the picture is fitted correctly? What do you think is right, and what do you think is wrong?

​Storage cisterns and the Water Regulations

​Schedule 2, Paragraph 16, of the Water Regulations tells us that a storage cistern supplying low-pressure cold water supply to sanitary appliances, or feeding a hot water storage system, should be capable of supplying potable, wholesome water

Open Ended

What is meant by the term: "potable, wholesome water"?

​Various protection measures must, therefore, be included in the design of the cistern to ensure the water supply does not become contaminated or unwholesome.

​To comply with the Water Regulations, cisterns must:

≻ be fitted with an effective inlet control device to maintain the correct water level, i.e. a float-operated valve
≻ be fitted with service valves on inlet and outlet pipework connections
≻ be fitted with screened warning/overflow pipes
≻ be covered with a rigid, close-fitting lid, which is not airtight but excludes light and insects
≻be insulated against freezing or undue warming
≻ be installed so that the risk of contamination is minimised
≻ be arranged so that water can circulate, preventing stagnation
≻be supported to avoid distortion or damage that could lead to leaks
≻be readily accessible for maintenance and cleaning

​General installation requirements for domestic cisterns

​Water is heavy.
At 4°C it weighs 1 kg per litre, so 230 litres will weigh 230 kg – almost a quarter of a tonne! From this, we can appreciate that a cistern full of water will need adequate support, especially if placed in a roof space.

​The platform that the cistern sits on should be covered with 21 mm tongue and groove boarding or moisture-resistant marine-grade plywood.

Labelling

Label the diagram

Drag labels to their correct position on the image

Insulation

Float valve to BS1212

Service valve

Multiple Choice

What is the purpose of an effective inlet control device in a cold water storage cistern, according to Schedule 2, Paragraph 16, of the Water Regulations?

• To exclude light and insects

• To maintain the correct water level

• To support the cistern

• To insulate against freezing

Multiple Choice

According to the Water Regulations, what measure should be implemented for the inlet and outlet pipework connections of a cold water storage cistern?

• Insulation against freezing

• Service valves

• Screened warning/overflow pipes

• Circulation prevention

Multiple Choice

Which of the following features is required for the lid of a cold water storage cistern to comply with the Water Regulations?

• Airtight sealing

• Exclusion of light and insects

• Adequate support

• Insulation against freezing

Labelling

Label the diagram

Drag labels to their correct position on the image

Screened warning pipe

25mm between overflow level and FOV

Screened vent

Multiple Choice

What is the recommended clearance for maintenance and cleaning of the float-operated valve (FOV) and the cistern, according to the information provided?

• 150 mm

• 350 mm

• 230 mm

• 500 mm

Multiple Choice

Why is it important to support a cistern over the whole of its base, especially if placed in a roof space?

• To prevent contamination

• To avoid distortion or damage

• To ensure insulation against freezing

• To provide clearance for maintenance

Multiple Choice

What is the weight of 230 liters of water at 4°C?

• 230 kg

• 345 kg

• 460 kg

• 575 kg

​Inlet requirements for domestic cisterns

​The inlet requirements state that all cisterns will be fitted with an adjustable water inlet control device.
These devices are usually float-operated valves that must conform to BS 1212.

​Part 1 – Portsmouth type (permitted only with a backflow prevention device) l Part 2 – brass diaphragm type

​Water outlet requirements for domestic storage cisterns

​The diagram shows the positioning of cold water distribution and cold feed pipes.
It is recommended that the cold water distribution 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 distribution pipe can be located on the side of the cistern.

The distance between the cold water distribution outlet and the cold feed to the hot water system should be not less than 25 mm.

Open Ended

Why do you think the cold feed pipework connection to the hot water cylinder needs to be 25mm higher than the cold distribution pipework connection

​​This is so that the hot water will run out first, which will prevent any potential scalding situation if any mixing valves, such as showers, bath mixers or monobloc washbasin mixers, are installed on the system.

​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 float-operated 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 float-operated valve.

​Materials for domestic cisterns

​Almost all new installations use cisterns made from plastics such as polyethylene, polypropylene and glass-reinforced plastic (GRP).

Most cisterns manufactured today are made from polypropylene because this allows:

≻lightweight construction
≻ strength
≻ hygiene
≻ resistance to corrosion
≻ flexibility, as they can easily be handled through roof space openings

​Cisterns are available either square, rectangular or circular in shape, and are produced in black to prevent the growth of algae.
However, because they are flexible, the base of the cistern must be fully supported throughout its entire length and width.

​Multiple cistern installations:
interconnection of two or more cisterns

​Where large quantities of water are required but space is limited, cisterns can be interlinked, provided the cisterns are of the same size and capacity.

​Stagnation can be avoided by following some basic rules.

Connection must be arranged to encourage the flow of water through each cistern. This can be achieved by:

​The primary outlet connection should be made on the opposite cistern to the float-operated valve to encourage water movement

Labelling

Label the daigram

Drag labels to their correct position on the image

At least 150mm all around base

350mm min for maintenance

No insulation under CWSC

Multiple Choice

Which standard do float-operated valves for cisterns need to conform to?

• BS 1212

• ISO 9001

• ASME B16.11

• EN 50291

Multiple Choice

What is the recommended location for the cold water distribution pipe connection to the cistern?

• Top of the cistern

• Bottom of the cistern

• Side of the cistern

• Inside the cistern

Multiple Choice

Why should the cold water distribution outlet be fitted 25mm below the cold feed to the hot water system?

• To prevent sediment build up

• To prevent scalding situations

• To allow for flexible handling

• To facilitate lightweight construction

Multiple Choice

where should the cold outlet be positioned in relation to the float-operated valve?

• On the same side

• On the opposite side

• On the top

• On the bottom

Multiple Choice

What material is commonly used in the manufacturing of cisterns today, providing lightweight construction, strength, and resistance to corrosion?

• Stainless steel

• Copper

• Iron

• polyethylene

Multiple Choice

Why are cisterns made from polypropylene preferred in new installations?

• Resistance to corrosion

• Lightweight construction

• Hygiene

• All of the above

Multiple Choice

To prevent the growth of algae, in what colour are cisterns typically produced?

• White

• Green

• Black

• Blue

Multiple Choice

How can stagnation be avoided in interlinked cisterns?

• Placing outlets randomly

• Connecting outlets to the float-operated valve

• Arranging connections to encourage water flow

• Using cisterns of different sizes