April 2020

Focus on: Pumps & Valves Process, Controls & Plant April 2020 www.pwemag.co.uk Plant & Works Engineering | 29 valve stem and the response time of the valve itself. Once complete, the valve is ready for normal operation. Improving safety Control valves should be specified so that they operate in the 40-85% range so if the valve is commanded to a 10% setting, it can detect that something has potentially gone wrong with the control system and the best course of action is to close the valve completely. If the valve is commanded to a position of 10% or less this can cause very high fluid or gas velocities, which have damaging effects on the system and cause considerable noise and damage to the valve itself. Modern control functionality can offer a solution that acts as a safety device to prevent damage to the process pipework and components. By building in a fail-safe mechanism, any valve position setting below a pre-set threshold will result in the valve closing completely, preventing damage to the surrounding system. Control inputs can also include safety circuits to ensure safe operating conditions within the process equipment. For example, if an access panel on a vessel containing steam is opened, an interlock switch will open and the valve controlling the steam supply to the vessel can be closed automatically helping to mitigate any risks. Improving reliability Many process control environments offer less than ideal conditions for long-term reliability. Moisture-laden atmospheres, corrosive chemicals and regular wash-downs all have the capacity to shorten the service life of a process control valve. One of the potential weaknesses of the actuator is the spring chamber where atmospheric air is drawn in each time the valve operates. One solution is to use clean, instrument air to replenish the spring chamber, preventing any contamination from entering. This offers a defence against the ingress of airborne contaminants by diverting a small amount of clean control air into the control head, maintaining a slight positive pressure, thus achieving a simple, innovative solution. This prevents corrosion of the internal elements and can make a significant improvement to reliability and longevity in certain operating conditions. Ultimately, choosing the most appropriate process control valve can be a complex task that is often best achieved with the assistance of expert knowledge. Working directly with manufacturers or knowledgeable distributors enables process control systems to be optimised for long-term reliability as well as precision and efficiency. Call 01664 567226 for more information www.dualpumps.co.uk Stock in excess of £3 million Request a copy of our latest catalogue Stock in excess of £3 million 35,000 sq. ft. distribution centre mo re than just pumps Pumps Cleaning Equipment Pressure Washers Hose Hose Reels Fluid Handling Fittings Connectors Filters Spraying & Watering Engines Motors Generators Frames UK Official Distributor Since 1983 Dual Pumps 178x124 April.indd 1 01/04/2020 10:03:20