FLOW & LEVEL CONTROL


ACCURACY OVER A LONG LIFE


Kieran Bennett, field segment manager for hygienic - food & beverage at Bürkert, explains the


technology behind Element continuous control valves


W


hile accuracy is the key requirement for a continuous control valve, it's 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% accuracy throughout a service life of seven million cycles - at least three times longer than conventional designs. Mainly 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. 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. Always accurate to within just 0.1% of the command position, this accuracy is continuously repeated across the valve's


Continuous control valves are often used in the brewing industry


lifespan. Taditional technology typically has a decline to 0.5% 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, the Element positioner uses a contactless induction sensor with no moving or contacting parts, hence no wear, and remains accurate to within 0.1% even after 10 years of use. A longer lifespan compared to traditional


designs, is also a key benefit. 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 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. Unplanned downtime, for example a mechanical breakdown through valve failure with a corroded spring, can also cause costly knock-on damage to


other parts of the system as a result. Alternatively, Bürkert's Element system is


sealed and prevents ingress of moist, contaminated air. The clean, dry air used to pressurise the actuator is recycled back into the spring chamber via an integrated pilot valve, preventing corrosion of the actuator spring and removing humidity build-up inside the actuator. This also removes the possibility of bacteria collecting inside the actuator, which could potentially contaminate the hygienic atmosphere. In addition, the positioner is also sealed and the area around the electronics is pressurised to keep out any moisture, contributing to the valve system's long life. With a durable, stainless steel body, the


Element continuous control valve is also free from external corrosion. It can be used in hygienic environments and can undergo a rigorous washdown with chemical solutions without pitting or degrading, which can attract bacteria. Similarly, the valves are designed for simple and effective cleaning, with the smooth edges reducing bacteria build-up and providing a clean, clinical look. The polished stainless steel finish also means there's no paint that can peel off in the hygienic environment and the high IP rating makes the valve durable against washdown and moisture ingress. As the Element continuous control valves


are more compact, they also use less compressed air. On average usage with 50 valves per site, a typical saving of £2,500 per year can be achieved by using Bürkert's more compact valves. The advantages of a smaller, lighter valve also include easier maintenance and pipework doesn't need any reinforcement whether for new or retrofit projects. The advantages of the Element system


can also be attributed to globe control, angle seat and diaphragm valves and the positioners can communicate with analogue control signals as well as all common Ethernet industrial networks.


Bürkert Fluid Control Systems www.burkert.co.uk


JULY/AUGUST 2021 | PROCESS & CONTROL 21


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