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HYDRAULICS 28 HYDRAULICS & PNEUMATICS March 2020 www.hpmag.co.uk Control valves are used to manage the flow rate of a liquid or a gas and in-turn control the temperature, pressure or liquid level within a process. As such, control valves are defined by the way in which they operate to control flow and include globe valves, angle seat, diaphragm, quarter-turn, knife and needle valves, to name a few. In most cases the valve bodies are made from metal; either brass, forged steel or in hygienic applications 316 stainless steel. Establishing the parameters Actuators use an on-board system that measures the position of the valve with varying degrees of accuracy, depending on the application. A contactless, digital encoder can place the valve in any of a thousand positions, making it very accurate, while more rudimentary measurements can be applied to less sensitive designs. One of the main areas of debate when specifying control valves is determining the size of the valve required. Quite often process engineers will know the pipe diameter that is used in an application and it is tempting to take that as the defining characteristic for the control valve. Of greater importance are the flow conditions within the system as these will dictate the size of the orifice within the control valve. The pressure either side of the valve and the expected flow rate are Process control valves – making the right choice Modern process control valves offer a wide range of features and benefits for industries that require precise control over fluids, steam and other gases. With so many control valves on the market, it is important to establish the features that will deliver the most cost-effective design for a particular application. Damien Moran, field segment manager, hygienic - pharmaceutical at Bürkert, looks at some of the basic differentiators as well as some recent design developments. Control valves are used to manage the flow rate of a liquid or a gas and in-turn control the temperature, pressure or liquid level within a process.