Modern, digital, electro-pneumatic valves that use micro-solenoid valves to control the air in and out of the actuator have introduced significant improvements for operators. It is important to not only establish the most appropriate valve design, but also a cost-effective solution that takes account of annual running costs. Older, pneumatically operated positioners had a flapper/nozzle arrangement and operated on 3-15psi, so no matter what the state of the valve, open closed or somewhere in between, the system was always expelling some compressed air to the atmosphere.Ĭompressed air is an expensive commodity, requiring considerable energy to generate and when a manufacturing line is equipped with multiple process control valves all venting to the atmosphere, this can equate to a considerable waste of energy. The actuator is topped off by the control head or positioner. Actuators are usually made from stainless steel or polyphenolsulpide (PPS), which is a chemically-resistant plastic. The piston design typically offers a smaller, more compact valve which is also lighter and easier to handle than the diaphragm designs. Inside the valve body, the actuator design is often either a piston or a diaphragm design. The pressure either side of the valve and the expected flow rate are essential pieces of information when deciding on the valve design. Of greater importance are the flow conditions within the system as these will dictate the size of the orifice within the control valve. Often process engineers will know the pipe diameter used in an application and it is tempting to take that as the control valve’s defining characteristic. One of the main areas of debate when specifying globe control valve is determining the size of the valve required. 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. In most cases the valve bodies are made from metal either brass, forged steel or in hygienic applications 316 stainless steel.Īctuators will use an on-board system to measure the position of the valve with varying degrees of accuracy, depending on the application. As such, they 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. With so many control valves to choose from it is important to establish the features that will deliver the most cost-effective design for a particular application.Ĭontrol 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.
Today’s process control valves offer an ever wider range of features and benefits for industries that require precise control over fluids, steam and other gases.
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