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Avoiding stagnation in the twin tank scenario

Neil Weston, Keraflo Sales Manager and ATCM Chair, discusses why so many consulting engineers and specifiers are turning to Keraflo to help with the safe re-commissioning, repurposing and refurbishing of buildings as well as future-proofing water safety during post-COVID flexing building occupancy levels

It has been widely reported that buildings being reopened following the Covid-19 lockdown have the potential for a greatly increased risk of Legionnaires’ disease due to water stagnation and absence of normal control measures. As uncertainty continues surrounding the Omicron virus, it doesn’t look like consistent, steady use of workplaces will happen anytime soon, with hybrid working set to continue.

We know that the Legionella bacteria develops in stagnant water, especially if the temperature rises, so the importance of water management should never be underestimated. While most facilities are good at undertaking risk assessments and addressing the need for water monitoring, technical problems can occur that can create an issue in this area. Anyone familiar with water system management will know there is one such common problem that rears its head when it comes to balancing twin cold water storage tanks.

Division of labour

Some buildings have a tank with a division within it or two tanks that are sized and designed to serve the demands of the whole building independently of one another. It’s a strategy aimed at preventing down time if one tank or division has to be shut down for cleaning or maintenance. However sometimes it becomes clear that one tank is doing all the work, leaving the other exposed to a risk of stagnating water.

This happens because whilst the water is drawn off from a common header, you will sometimes find that the float valves are installed at slightly different heights due to all sorts of influences, such as the accuracy of the height of the fixing holes, or even if the floor isn’t quite level. In addition, the distribution pipework is often not even. The consequence of this is that one valve will operating at a slightly different water pressure, albeit very minor.

Balancing act

In this twin tank scenario, you also have to take into account the orientation of the valve in the tank – the positioning of the two will vary, even if only by a degree or so. If therefore one valve comes on slightly before the other and keeps up with the demand from the building, the other filling valve will not activate. Once this starts to happen the problem becomes worse because generally valves prefer to be exercised, so the valve that operates more often becomes looser while the other becomes stiffer, further exacerbating the issue.

Top tips

There are however things you can do to try and get the valves to operate in tandem. For example, it might help to rotate the valves slightly, as well as checking the height settings. If you rotate the dominant valve that is operating all the time marginally anticlockwise as you stand behind it looking into the tank, it will delay it slightly. If you ensure the valve that is not operating correctly is turned clockwise until the bubble on the spirit level is just touching the black line, this may do the trick to correct the imbalance.

Unfortunately, even when these minor issues have been overcome and the valves operate simultaneously, it is something that needs to be monitored because there is no guarantee that mechanical float valves will wear at the same rate.

Simultaneous tank filling

Keraflo works closely with customers to overcome these issues in the first place or aid them in putting them right further down the line, but for those looking for a more reliable long term solution, we do also manufacture valve systems that guarantee that both sides of the tank fill simultaneously.

The WRAS approved Aylesbury KP Float Valve system and Tanktronic electronic management products are designed for precisely this purpose and have been utilised successfully across many types of buildings. The unique KP Twin Float Valve Kit is specifically designed for twin tank/partitioned tanks. It uses a KB delayed action pilot valve in each tank or division. As the water level drops, whichever pilot valve opens first actuates the main control valve filling both sides simultaneously whilst still giving the option of isolating one tank or division leaving the other side in service. 

The next level of tank performance and safety is Tanktronic. This unique WRAS approved modular electronic tank management system provides a simple solution to monitoring water levels, volume and temperature through one connection. Tanktronic’s innovative ‘flex functions’ (aka holiday functions) means you can have different water levels for different times of the year, weekends, and even different days of the week. So, if you know building footfall will be higher on say the first and last day of every week, you can set Tanktronic to automatically manage this. You can even take the guesswork out of sizing the tank and ensuring turnover, by using one of these flex settings so that you empty most of the tank before refilling at a regular interval, say perhaps once every week. Tanktronic can also be set up to fill two tanks simultaneously.

Perfect for retrofit and refurbishment projects as well as new constructions, our user-friendly solutions are are quick and easy to install and offer a complete cost-effective solution to water monitoring and filling with some very advanced options increasing its usability, efficiency, safety and most significantly, flexibility. 

For further information you can view The Tanktronic Leaflet, Servo Ceramic Valve (SCV) and the Tanktronic Datasheet, you can also watch the Installation Video.


Case Study

A Twin KP Float Valve system is ensuring constant supplies of fresh cold water from hospital storage tanks at the Garrett Anderson Centre (GAC), a self-contained building within the Ipswich Hospital complex. The GAC is supplied with water through a break tank on the ground floor that, in turn, feeds a storage tank in the roof through a booster set. Both tanks are divided into two, which provides easy maintenance and cleaning access while ensuring an uninterrupted supply of water to the 24/7 facility.

As we have seen above though, there are problems with having a divided tank that need to be addressed. The Keraflo Twin KP Float Valve system was developed with Kier Construction to overcome these problems and offers a unique solution to meet market needs. The Twin KP uses two main control valves, one on each side to fill the tank, supported by two smaller pilot valves. The two main control valves are triggered by the pilot valves; whichever pilot valve opens first then opens both control valves simultaneously, thereby filling both sides of the tank.





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