Reliable technology01 June 2006

As a function of quality management, reliability is defined as a measure of the degree to which a system does what it is intended to do. Clearly, reliability is crucial, and all manufacturing processes require safe and reliable operation of valves, whether the fluid controlled and directed is harmless or hazardous, from air handling, fluids, vapours, gases and waste.

Innovative valve design, choice of materials and construction all have a part to play. Ideas such as including actuating mechanisms within the valve body reduce the footprint, while integrating seals in a sub-assembly on the pump body minimises downtime and reduces operating costs. Manufacturers consider that automation will increase with the application of valve technology and lead to the delivery of energy, quality and manpower efficiencies.

Many industrial processes are dependent on the use of steam, including the manufacture of seals and gaskets, food processing, paper, textiles, chemicals and pharmaceuticals, biotechnology, some car manufacturing applications and even the curing of rocket propellants.

An interesting example of process improvement with steam flows in the beverage and food processing industries uses intelligent valve positioners, or 'smart positioning', for British Bakels. The company makes a range of ingredients for commercial bakeries and these highly accurate positioners control the valves to within 1% of their travel. Accurate temperature control is vital when processing bakery ingredients, and the Spirax Sarco SP2 smart positioners are fitted to the pneumatic controls that regulate cooking and chilling temperatures for this company. By using digital air control to provide near-zero air consumption at the set point in the British Bakels installation, they also enable energy savings to be made. Positioning devices provide the interface between the air-operated valve and its control system, with connectivity to HART, Profibus PA and Foundation Fieldbus protocols, enabling remote device setup and management.

Correct sizing of valves is essential for precision in process operations, together with improvements in system and environmental safety and quality. The traditional 'rule-of-thumb' method where the valve is oversized 'just to be on the safe side' is a myth, with experience showing that oversizing is as bad in its effects as undersizing.

Oversizing leads to unnecessary costs and operational problems, a number of which can impair the life of valves. The downsides are variable or erratic control of flow, oscillating of internal parts to maintain the required pressure and erosion of valve seats. With undersized installations, the problems can appear even worse - the obvious inability to cope with the required flow, a fall in outlet pressure and losses in the pipe network.

With the environment playing an increasing part in all manufacturing industry, one of the greatest needs is to ensure that glands and seals connecting sections of pipework, pumps and valves are as leakproof as possible.

To this end, world renowned companies, such as James Walker, have developed control gland packings that meet the stringent requirements of VOC emission levels specified by ISO15848. One of the company's latest innovative developments uses a high purity graphite ribbon, with a form of reinforcement that can be used at temperatures of between -200oC to +350oC. A major advantage for this seal and material is that, unlike conventional PTFE vee ring seals, it does not need a spring-loaded gland follower, even at pressures of more than 200bar.

As with the other industries, minerals and extractive processes are driven by the need to maintain environmentally sustainable, safe and reliable operations. Weir Pumps' Netherlands division recently delivered six extremely large diaphragm pumps to Brazil, to transport iron ore concentrate as 70% solids to 30% water suspension, along a 396 kilometre pipeline. Ensuring a leak-free operation, sensors or transducers are used to provide piston stroke reversal, controlled through a PLC. This allows the use of standard hydraulic piston seals, whilst providing effective leakage compensation.

Modern valve designs offer many opportunities to improve safety and the effectiveness of the manufacturing process. Take the example of hydraulic systems, such as those used on lifting and loading platforms. One of the latest designs of line rupture valve, screwed directly into a system component, protects against the effects of a tube or hose failure by closing immediately in response to a large change in the flow rate. This not only prevents any further flow of hydraulic fluid, but can also hold the load safely in place, or allow it to be lowered in a controlled manner.

Many process valve operations are conducted in hazardous environments, but require operational cycles of only a few milliseconds. Typical applications would include shut-off, dosing, filling and actuator piloting, and food machinery, heating and refrigeration equipment, washing machines, petrochemical machines - and even the car wash.

Asco Joucomatic has developed a novel design of stainless steel direct-acting valve capable of a 20 million cycle service life, and 5 to 10 millisecond operating time. A key element is the valve's square core, which contributes to preventing build-up of calcium when used with water and, when operating with contaminated fluids, prevents the valve core from malfunctioning. Other features that provide operational benefits are the lower friction with the square core, making the valve more efficient, and a shock absorber fitted to the top surface of the core, reducing operating noise from fluid hammer.

However, it is not just the product element that contributes to the application of safe and reliable valve technology. Valve manufacturers recognise the business, environmental and human risks associated with the failure of critical service and isolation valves, and many, such as Weir Group, now invest heavily in maintenance and support arrangements with customers. This enables products to be more effectively targeted through enhancements and upgrades, delivering operational benefits directly.

Similarly, the provision of training from manufacturers such as Spirax Sarco offers additional benefits to engineers working with and on these products, as functions remain constant, but the form or operational controls are enhanced.

The partnership approach is key to success in customer-supplier relationships, and is contributing equally to the benefits offered by innovation in valve design and technology, including the continuing expansion of automation and intelligent control at the device level.

SOE

This material is protected by MA Business copyright
See Terms and Conditions.
One-off usage is permitted but bulk copying is not.
For multiple copies contact the sales team.