Safer liquids transfer
April 1st 2006 Asked to name dangerous industries, few people would include food and beverage manufacture.
However, statistics from the Health and Safety Executive show that these industries account for around one quarter of all industrial injuries. The incidents which give rise to these take many forms, but a significant percentage involve road tankers that drive away without uncoupling the hose that connects them to the fixed plant. One solution is breakaway couplings, as John Quilter explains
A breakaway incident can have a host of serious consequences. Tension in the hose before it snaps can cause extensive damage to both the tanker and to the fixed plant, resulting in down time, and substantial repair costs. The hose will almost certainly be destroyed and, even worse, when it finally parts as the tanker moves away, it is likely to whiplash, creating the possibility of serious injury to persons in the vicinity.
In theory, it should be possible to eliminate breakaway incidents simply by implementing and enforcing good working practices. In reality, however, some risk will always remain, especially as today's working environment creates pressures for tankers to be turned around in the shortest possible time.
Clearly, there is a need for some form of automatic fail-safe preventative system.
In principle, implementing such a system should be straightforward. All that's needed is a hose coupling which will pull apart when the tension in the hose rises above a predetermined level. Analysing the requirements more closely, however, shows that designing a coupling that has the necessary qualities is far from easy. For a start, it must part reliably at a pre-defined level of hose tension, which must be sufficiently low to minimise the risk of any serious whiplash effect. However, it must remain intact under all normal operating conditions, and when subjected to rough handling. The separation performance should be maintained throughout the coupling's working life, preferably without the need for maintenance, and it should be possible to restore that performance easily and reliably after a separation incident, so that the coupling is quickly back in service.
Many design approaches are possible. One that satisfies the above requirements at an affordable price is based on the use of specially fabricated connector pins to hold the two sections of the coupling together. These are precision-machined components, the key feature of which is a narrow waist. At a certain level of tension, these pins start to stretch at the waist. As they do so, the waist narrows still further and the pin stretches increasingly easily. The net effect is that once stretching has started, it proceeds almost instantly to the point where the pin fractures. The breaking tension of the pins is, therefore, very well defined.
This means that the couplings in which they are used have a well-defined parting tension. This can be chosen to be significantly higher than the hose will experience in everyday use, but lower than the critical whiplash tension. Provided that they are made from corrosionresistant material, the pins will not significantly degrade with age, however long the coupling is in service. In addition, after a breakaway incident, the coupling can easily be brought back into use simply by fitting new connector pins, and its performance is then guaranteed to be equal to that of a brand new product.
While the connector pins are the key to the design of a reliable and effective breakaway coupling, in a practical product there are other important factors which must be considered. The material from which the coupling is manufactured must, for example, be resistant to corrosion and compatible with the products that are being handled.
For applications in the food and beverage industries, 316L stainless steel is a suitable choice.
In those industries hygiene is a prime concern, and this means that the couplings need to be carefully designed to eliminate crevices and traps that might otherwise harbour stale product or contaminants. In many cases, it will need to be capable of withstanding high temperatures, sudden temperature changes and the aggressive chemicals associated with cleaning in place procedures.
Finally, however good the couplings, they are of little value unless they are compatible with the hose fittings which are used by the customer. The best breakaway fittings should, therefore, be available in a variety of standard sizes, ideally with an option for them to be adapted to suit proprietary end fittings.
Breakaway incidents are one of the most common problems associated with the transfer of liquids to and from road tankers. They can have expensive and dangerous consequences, but are easily eliminated by using well-designed breakaway couplings. Types based on breakable coupling pins are recommended, as they offer reliability, performance and value for money.
Bulletin John Quilter is sales and marketing director of FlexRite Chemgiene, a supplier of fluid handling products to the food, brewery, beverage, dairy, pharmaceutical and chemical industries.
The company offers hose management services, including testing, surveys and RFID hose tagging.
Hygienic hose, industrial and chemical hose, and washdown equipment form the main product groups.
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