Fitting regulations for backflow technology

Danfoss' product manager Ian Ward describes an alternative to the type A air gap system for backflow prevention, the RPZ valve, which is now legal in the UK following changes to the water supply regulations.

At the start of this month, the Water Byelaws Scheme was replaced by the Water Regulations Advisory Scheme (WRAS), following the introduction of the Water Supply (Fittings) Regulations 1999. The move will bring about some interesting changes.

The move arises out of a need to make codes of practices easier to understand and to harmonise the UK regulations with those of Europe.

Focus on backflow
Greater compatibility of regulations also extends to the technologies now in use in keeping water safe and free from contaminants. The problem of backflow, for instance, has come in for some considerable attention. Backflow occurs when flow in a water distribution system is reversed ­ creating the possibility of drawing in contaminants. Backflow can lead to the degradation of industrial or domestic water supplies.

To prevent this contamination, the WRc (Water Research Centre) which will administer the WRAS, stipulates that a protection device must be used. Until recently the only universally applied system in the UK which had been officially ratified by the WRc in Byelaw 25 was the type A air gap system. However this remedy was not without its problems. For example, the air gap system necessitates the water supply being open to atmosphere, therefore allowing the possibility of debris and bacteria to enter the supply. Also, because prolonged storage of a small amount of water is necessary for the system to function effectively ­ the water may not be thought clean enough for some industries, such as the food industry.

The RPZ solution
An alternative to the type A air gap system is a mechanical device that controls backflow by reducing the pressure zones - generally known as an RPZ valve.

Danfoss has been using the RPZ valve, through its Socla valve range on mainland Europe and in the US for over 25 years.

Although accredited and used by several UK water authorities, until now it has not been widely used in the UK. The relaxation of the type A air gap stipulation means that industry is now freed up to use the RPZ valve and is beginning to fully appreciate its benefits.

But what exactly is an RPZ valve and how does it work? Basically the technology is very simple. The valve protects the potable water supply by interrupting the continuity of the supply to the user automatically whenever there is a shift in pressure.

This technology can be put to use in virtually any network ­ no matter how complex. For example many different industries, agricultural, chemical and general industrial are served by the same mains supply network, but of course may be operating different in-house systems, with water pressures that differ from that of the mains.

The Socla range of RPZ valves will work with any system no matter how complex or seemingly incompatible ­ guaranteeing a pollution free solution. There are several advantages of using the RPZ-type valve. In food processing, for example, the use of RPZ valves could remove the cost of maintaining large holding tanks ­ usually in a roof space - which comply with the type A air gap system. Removing these tanks could save space and minimise plant investment costs.

There is also the actual cost of the valve ­ if the price of a pump and break tank are taken into account, there can be savings of 80% ­ including labour.

The RPZ simply fits into the supply system, all working parts can be accessed quickly and no extra piping is required. The addition of an RPZ valve will not only reduce maintenance requirements but eliminate the need for a separate pump, as mains pressure is maintained at all times.

Strict monitoring
Both type A air gap systems and RPZ valves must be subjected to strict maintenance and monitoring procedures under the regulations, with at least an annual performance check for which the user is responsible.

The Socla RPZ valve range has two kinds of maintenance kit for quickly monitoring performance.

A check list is included with the kit which explains the test method and functionality of the following:

- upstream stop valve

- discharge valve

- stop valve

- downstream check valve

It also tests the differential pressure, which triggers supply disconnection. The kits ensure that maintenance ­ and compliance with regulation testing ­ is a simple procedure.

Five Fluid Categories
There are some instances when the RPZ valve would not be suitable for use. It is believed that plans are afoot under the WRAS for five categories of fluid ( previously only three).

The categories will range from one ­ for potable, wholesome water ­ through to five, for water with serious contaminant possibilities. The latter category covers radio active fluids and fluids containing life-threatening pathogens, for which the RPZ valve would not be suitable. In conclusion, the harmonisation of the of anti-pollution systems with European standards is likely to have a positive effect on manufacturing industry.

The previous system of byelaws in the UK sometimes meant that what was legal in one district was outlawed in another. A confusing and unsatisfactory state of affairs.

Now that RPZ valves have been accredited, potential customers have a wider choice and will be able to make an informed decision based on suitability and cost.


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