Balluff Transducers for partial-stroke testing on hydraulic valve drives

The right sensors for advanced partial-stroke test systems

© 2015 Balluff GmbH

Cross-section view of a transducer in a rod design with a magnetic encoder ring, built into a hydraulic cylinder. © 2015 Balluff GmbH

One ideal application area for Micropulse® transducers in a rod housing is providing position feedback for hydraulic cylinders in valve drives. They are therefore often located in linear-activated fixtures like stop valves or seat valves, but also in ball valves and shutoff gates with swivel activation in combination with special drive mechanisms (such as Scotch yoke, rack-and-pinion drive, etc.).

Partial-stroke testing of cylinders opens up another area of application in combination with the diagnostic options of smart position regulators. Using the absolute signal, the operating suitability of the valve can be monitored during ongoing operation, between the tests already scheduled during downtime. This results in fewer service interruptions and unscheduled stoppages for the system operator. Models with Ex approval are regularly used in explosive atmospheres, found in the Oil & Gas industry and in power plants.

Wear-free and maintenance-free

Micropulse transducers work without making any contact and are entirely wear-free and maintenance-free, providing the user with an extremely long service life.

For measuring the position feedback of a valve, the transducer is installed on the back end of the drive cylinder. The actual sensor element is installed into a hole that runs lengthwise, passing through the piston and the cylinder rod and reaching over the entire mechanical stroke length. A magnet ring, located in an indentation on the end face of the piston, acts as the position encoder.

Partial-stroke testing made easy

Logging the speed of the valve movement over time allows the user to detect wear, corrosion or abrasion in the valve before they worsen and cause negative effects. Common symptoms of pending malfunction may include such aspects as the valve reacting slowly or with a delay, or its required deflection is not completely achieved.

Ex models for global use

Explosion proof models of Micropulse® transducers from Balluff are some of the few position-feedback devices on the market that not only have all basic certifications from start to finish, such as ATEX (EU), IECEx (international), NEC (US), CEC (Canada), but also additional regional qualifications for India, Japan, and Korea. Not only does this simplify the design and global sale of standardized systems, it also helps to prevent expensive errors in the project planning phase.

Source: Balluff GmbH