Precision, service life and accuracy are the valve essentials
4 May 2022
Accuracy may be key for a continuous control valve, but so is maintaining precision and service life, says Kieran Bennett who explains Bürkert’s solution.
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.
Ttraditional 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. 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% even after 10 years of use.
The key benefit of the Element continuous control valve system, 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 the 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 & 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.
Bürkert’s 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.
A highly durable, stainless steel body means the Element valve is also free from external corrosion and being more compact, uses less compressed air. By their nature, continuous control valves can be in near constant motion so the savings to be obtained from air usage can be significant across a plant.
Kieran Bennett, Field Segment Manager for hygienic-food & beverage at Bürkert
