BSEE
Kevin Belben, technical applicaons manager at water management specialists Cistermiser and Keraflo, tackles some of the common challenges thrown up by the ulisaon of twin tanks
A
gainst the Covid-19 backdrop, it may not feel a high priority at the moment, but with an average of 250–
300 reported cases of
Legionnaire’s disease among UK residents every year, it’s a not insignificant public health risk. In 2019, this figure doubled to 516. While it’s the elixir of life, water also has the capacity to be a silent killer, as the medium for the transmission of several infectious diseases. Water-borne diseases are predominantly caused by pathogenic microorganisms – bacteria, intestinal parasites, protozoa, viruses, etc. – that contaminate municipal water supplies. We know that the Legionella bacterium can develop in stagnant water, 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.
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.
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 delayed-action 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.
WATER TREATMENT Twin Tanks: a balancing act
Typical Twin Tank installaon schemac 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
Cistermiser and Keraflo work 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 Aylesbury KP Float Valve system and Tanktronic electronic tank management products were designed for precisely this purpose and have been utilised in many facilities successfully.
The big picture
The use of twin tanks in substantial commercial premises undoubtedly has its advantages, so it is our job as water management specialists to offer advice and solutions where possible, to ensure this design approach remains a viable and safe option for our customers.
Aylesbury KP float valve system pilot valve
20 BUILDING SERVICES & ENVIRONMENTAL ENGINEER JUNE 2020
Visit
www.ourworldiswater.co.uk for more information or
www.keraflo.co.uk
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www.bsee.co.uk
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