Ball Sector Valves for precise control & isolation in harsh plastic production application
The Ball Sector Valves replace control valves in challenging applications – read this application story to learn more.
Ball Sector Valves for Isolation & Control
Ball sector valves are used as isolation valves and control valves for fluids, gases, turbid media and sludges, especially in the pulp and paper and chemical industry. With pneumatic and electrical actuators, ball sector valves are the best choice for challenging applications that require very precise control.
Faced with an expensive control valve failure, global supplier of high-performance engineering polymers, Ticona turned to a ball sector valve after an expensive control valve malfunction. The harsh conditions in fibre enforced plastic production at their plant meant that abrasion and corrosion occurred on the body, tapered seat or plug after only a short time, leading to total failure.
Thomas Labahn, the person responsible for plant planning and EMC at Ticona, conducted a parallel test of a ball sector valve from Schubert & Salzer and one from a rival manufacturer. The latter valve lasted precisely three weeks before seizing up but the former lasted the course.
Ball Sector Valves in Stainless steel
The valve is made from standard material (stainless steel) and only has hard chrome-plated (stellited) ball sector surfaces, making it significantly less expensive than the terminally damaged valve made from HastelloyC. Furthermore, the damaged valve can be repaired and even costs a good deal less to buy than the plug valve made from HastelloyC.
Innovative design of the Ball Sector Valve
The ball sector valve consists of a hemispherical shell – the ball sector – that is held securely in the valve body using two large bearing stems. Part of the hemispherical shell is used for isolating, while the other has a hole with a diameter corresponding to about 80% of the nominal size of the valve. The ball sector is turned through about 90° from fully open to closed.
Reduced risk of blockages
The shape of the opening cross section changes from completely round to elliptical in this case. This practically round shape for the flow opening reduces the risk of blockage when small control settings are made. The valve characteristic maintains almost the same percentage value with constant differential pressure.
Equal percentage operating characteristics
The modified equal-percentage operating characteristic (in operation, the differential pressure increases as the valve closes) combined with the outstanding rangeability of 300:1 mean that that valve can be used for most control tasks. The special connection of the valve body ensures that the differential pressure on the valve has little effect on the actuating torque.
Excellent control accuracy
Labahn says: “The media flows through the ball sector element in a totally different way than in the plug valve. In our case, the control accuracy that has been achieved is comparable to that of the plug valve we used to use.”
Ball Sector valve for control in challenging applications
After ten months in operation, only the holder of the seat ring had come loose, and the manufacturer is already working on a solution to this problem with an improved variant. Considering the numerous control functions in which these valves are used at Ticona – under extremely challenging conditions – the potential savings were quite considerable.
Ball Sector valve require low actuation thrusts
Other important aspects in favor of using ball sector valves are their comparably light weight and relatively low actuator thrusts. The friction against the stuffing-box seal in plug valves means they have a very high break-loose torque and this explains why they need powerful actuator thrusts.
The torque with the ball sector valve, on the other hand, is relatively low and the actuators can be correspondingly smaller. A single-action Wirematic actuator with a safety position is used on the valves. Furthermore, the valve does not get blocked because the entire pipe cross section is left unobstructed when the ball sector is fully open.
Does the Ball Sector Valve sound like a solution to your control valve failure problems?
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