Plant manufacturers are often faced with the challenge of determining exactly the right valve/manifold application for extreme operating conditions. For process plants, AS-Schneider can recommend the use of metal seated ball valves if abrasive products, high temperatures and pressures are present. Extreme operating conditions with temperatures up to 450°C and pressures up to 420 bar require a special sealing technology for ball valves. Standard soft seated ball valves simply are not ready for these kinds of requirements. Their plastic seats would fail.
Figure 1: Seat and ball surfaces are coated with Hardalloy and Carbide compounds at the metal seated ball valve of AS-Schneider.
Does tightness contradict a smooth actuating torque?
In a conventional design, the compression force (for the graphite seals on the ball seat towards the body) is applied directly via the ball, which also increases the contact pressure of the ball seat on the ball as the seal is compressed. This increased contact force has a negative effect on the actuating torque. The ball runs very heavy. Therefore, many manufacturers limit their metal seated ball valves to a maximum allowable pressure of 100 bar – because that is the limit that still permits actuation of the valve.
Figure 2: Conventional ball valve design – the forces required to maintain the tightness are stressing all components – even the ball and seats. The operating torque is thus very high.
If the applied force is reduced, actuation becomes easier, but then the compression of the graphite seal on the seat retainer is not sufficient to seal up to 420 bar reliably. Leakage occurs around the ball seat.
So, what now? This problem has not been ignored by the development team of AS-Schneider. They started looking for a solution and developed the 'Dissolution' ball valve design. The patented design offers optimum distribution of forces and loads in the ball valve, so that they only occur where they are actually needed. This means that the ball valve can be actuated easily, even under high pressures up to 420 bar.
How it works – 'Dissolution' ball valve design
The forces needed to maintain the tightness between the ball seat and valve body are only directed onto the corresponding graphite seal rings. The ball is only spring-loaded, which ensures a low, defined, minimum pressure off the balls on the ball seat. The operating torque can thus be significantly reduced, allowing the operator to operate the ball valve easily. At the same time, this construction offers maximum tightness and long service life.
Figure 3: 'Dissolution' ball valve design – the forces needed to maintain the tightness between ball seat and valve body are only directed onto the corresponding graphite seal rings. The ball is only spring-loaded, which ensure a low, defined, minimum pressure off the balls on the ball seat. A smooth operation is the consequence.
Read the article online at: https://www.worldpipelines.com/product-news/02072018/new-ball-valve-design-by-as-schneider/