WET News

Bare necessities MAY 2014 WET NEWS 23 THE CONCEPT • One-piece tanks are moulded in one piece, giving a smooth internal surface • There are no internal stays or lid support • The tanks can prevent water contamination • Leakage is prevented as there are no joints • The tanks show little deterioration NEED TO KNOW 1 There are cases of hollow tubes having been used to support lids in sectional cold water storage tanks, according to a recent government alert 2 These supports can cause stagnant water A recent Department of Health document has raised alarm bells over the use of hollow tubes for lid support in tanks, which can lead to stagnant water. The challenge: Preventing stagnant water in storage tanks T he relatively recent Depart- ment of Health's Estate Fa- cilities alert (EFA/2031/004) shows how changes in design and the inevitable wish to hold down prices can have serious side effects. The alert highlighted that some tank manufacturers have utilised hollow tubes to sup- port the lids in sectional cold wa- ter storage tanks. These supports, which are held in position by internal brac- ings, can create stagnant water that may allow biofilm and slime growth. This contaminated water can harbour micro-organisms such as Legionella and Pseudomas. Forty years ago many medium- sized and larger water storage tanks did what they were designed for – they held water for many years. They were made up from 4Š square metal sections and were bolted together with a joint sealant. The strength of the side panels were given extra sta- bility by bolting angle iron or simi- lar strengthening ribs from a floor joint at 45° up to the side joint. Depending on the size strong horizontal ribs or beams were bolted across the top from one side to the other, many of these ribs or beams gave the support to the top sides of the tank as well as supporting the roof plates. Grit blasting The internal surfaces of these very strong metal tanks were INSIGHT WATER TREATMENT Top and Bottom: One-piece tanks are moulded in one piece, ensuring a smooth internal surface as well as no joints. Ribs are used to strengthen the external wall and lid laminates quite oŠen coated with bitumastic or other coatings that were quite rough but pro- tected the metal plates, supports and bolts from rusting. Upon inspection aŠer grit blasting a large number of these metal tanks were still found to be too corroded to be repaired and their suitability, particularly if they were storing drinking water, questionable. What all these old metal tanks had in common in com- parison with modern ones is that they did not have pipes going up from the floor to support the lid, which has created today's prob- lems of stagnant water spots. The need for a new modern approach to water storage became obvious and around this period various manufacturing groups and committees were formed. The aim was to produce water tanks that would not corrode. A few manufacturers went in the direction of the simple plastic tanks seen in many houses, oth- ers turned to the stronger fibre- glass moulding. n With strengthening ribs in the external wall and lid, and featuring no joints, one-piece tanks can eradicate contamination A solution: One-piece tanks W hen the first fibreglass moulded tanks were developed it was a great step forward, with consult- ants and water engineers specify- ing the new non-corrosive one- piece tanks and sectional panels. When some of the fibreglass manufacturers went in the direc- tion of sectional panels others, like Precolor Sales, chose to develop their one-piece tank range further by moulding larger and larger self supporting one- piece tanks that, as the name suggests, are moulded in one piece giving a smooth internal surface. The strengthening ribs are encapsulated in the external tank wall and lid laminates. This quite simply means that no internal stays or lid support required. There is no hollow pipe or uncapped areas to hold or create stagnant water. The tanks were designed with these problems in mind. WRC-approved materials were required for manufacture. Resin suppliers quickly became involved helping to ensure that only quality products came onto the market, creating the modern WRAS-approval system. Bracing The early fibreglass panels were produced to the same dimen- sions as the old steel tank pan- els, 1,220mm x 1,220mm. Within a short period of time these sizes changed to 1m x 1m and 1m x 0.5m. In recent years, some sectional tank manufacturers have striven to be more and more competitive by reducing the integrity of their pan- els and relying increasingly on stay rods and internal supports. They are light in weight and many require the use of internal bracing going from one side of the tank to the other. These stay rods and lids can sag and require a method of sup- port. Perhaps the most logical answer is solid vertical supports with surfaces that can be seen and if necessary cleaned. Precolor continues to manufac- ture sectional panels at all sizes to suit requirements, heavy duty enough not to rely on internal stay rods, bracings and supports. Why are so many sectional tanks already installed with pipes holding up these stay rods and lid sections? Perhaps the answer is cost. Should the installation of one-piece tanks that carry a ten- year warranty be considered as a necessary alternative to sec- tional tanks to avoid preventable contamination? According to Precolor, consult- ants and water engineers should have the confidence to specify one- piece water tanks given the length of time that these tanks have now been in service, showing little dete- rioration and no joints to leak and with Precolor's range of sizes up to 97,000l. n "Forty years ago many medium- sized and larger water storage tanks did what they were designed for – they held water for many years"

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