Flow, level & control
Long Life and Long-term accuracy for continuous controL vaLves
While accuracy is the key requirement for a continuous control valve, it is crucial that precision is maintained over time. To reduce downtime and overall cost, the valve also has to maximise service life. Delivering these criteria, Bürkert’s Element continuous control valves achieve 0.1 per cent accuracy throughout a service life of seven million cycles - at least three times longer than conventional designs. Here, Kieran Bennett, field segment manager for hygienic-food & beverage at Bürkert, explains the technology behind Element continuous control valves.
M
ainly used within the food, beverage and pharmaceutical sectors, continuous control valves, also
referred to as modulating control valves, are crucial for accurate control of gases and liquids. Used across a variety of applications where high accuracy is required for temperature, pressure or flow control, continuous control valves constantly monitor valve position and make adjustments several times per second to ensure precise control of the media. Typically used for steam control within heating systems such as heat exchangers, continuous control valves are also important for accurate modulation in plants such as bioreactors, dairies, breweries and pharmaceutical production. This level of accuracy is achieved with the
partnership of the actuator and the electronic positioner, and Bürkert’s Element continuous control valve system is always accurate to within just 0.1 per cent of the command position. This gives a very high level of precision control and crucially, this accuracy is continuously repeated across the valve’s
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lifespan. This is significant because traditional technology typically has a decline to 0.5 per cent accuracy or more within as a little as 18 months of generally expected use, impacting the performance of the application accordingly. Typical position sensors use potentiometers
with contacts and linkages that wear out over time; the greater the number of valve cycles, the greater the wear. Instead, Bürkert’s Element positioner uses a contactless induction sensor with no moving or contacting parts, hence no wear, and remains accurate to within 0.1 per cent even after 10 years of use.
Up To sEvEn TimEs longEr lifEspan THan TraDiTional DEsigns The key benefit of the Element continuous control valve system, however, is its significantly longer lifespan compared to traditional designs. With an expected lifetime of seven million cycles, this is at least three times higher than the alternatives. In the case of diaphragm valves, the difference can be as much as seven times, where replacement of a diaphragm valve
after around a million cycles is common. This difference lies in the design of Element’s air
system. With conventional technology, air pressure opens or closes the valves against the force of the spring but when the valve is de-energised and the springs decompress, ambient air is introduced to the chamber. Ambient air includes moisture and in humid and potentially corrosive environments, such as a food and beverage manufacturing site that is subjected to regular chemical washdowns, the moisture and chemicals can rapidly corrode the valve’s steel spring. Not only does this lead to decreased
performance over time, it means a more frequent rate of replacement. This is not only more costly in the long-term with the replacement of valves, but it also increases the downtime required for the refit. Shutting off part of a high-value production plant for several hours can result in thousands of pounds of lost revenue, so minimising downtime is an important consideration. If that downtime is unplanned, for example a mechanical breakdown through valve failure with a corroded spring, it can also cause costly knock-on damage to other parts of the system as a result.
October 2021 Instrumentation Monthly
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