The ideal ball valve torque - Valve World

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Keywords: Leakage • Sealing • Torque. The ideal ball valve torque. The quest to find the ideal torque for soft seate
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FUGITIVE EMISSIONS

Keywords: Leakage • Sealing • Torque

The ideal ball valve torque The quest to find the ideal torque for soft seated ball valves, particularly from PTFE compounds without mechanical spring systems has a long history of failure.Generally speaking you have to consider the different manufacturing processes of the basic components. On the one hand the manufacturing of the sealing for the ball and secondly the manufacturing of the housing of a modern two part ball valve made from metal base material, these manufacturing processes are so widely different. The problem with using this process is it is very dependent on the considerable different characteristics of both the soft and hard materials to mix without negative reactions on the operating performance. Fig. 2.

f you take a close look at the seat ring you will see a block ring with a one sided machined calotte outline on the contact surface. On the bodies you will recognize that each of them is added with a mechanical machined slot to adjust the plastic sealing ring. The ingenious cooperation of the sealing geometry and modality of the sealing ring slot will achieve the required result. This result is the low torque and absolute tightness through the complete spectrum of the designated use of the ball valve. Previous knowledge of how PTFE compounds behave and react in different conditions is crucial for understanding in particular their behavior under

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Fig. 1.

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temperature and pressure. If there is temperature of ca. 19° Celsius PTFE will enhance its erratic volume. This is usually only expected in higher temperature ranges. Furthermore you have to examine the flow characteristics as PTFE begins to change its form under pressure during ambient air temperature. After this process is launched it will at no point revert to its previous form with high temperature only amplifying this effect.

A different approach A+R Armaturen GmbH has found a simple approach for the effective troubleshooting of the sealing geometry, using to their advantage the negative

characteristics of PTFE. They designed, from the originally simple block ring, a unique and effective geometry which compensates the complete volume change. In addition it is using the PTFE characteristics for controlling the preloading of the sealing on the ball. Of critical importance is the machining of the slot which is inside the housing and adjusted with the ball sealing. A simple angle is of no use as the sealing ring must be accurately adjusted inside a slot with a triple sided stabilization. The flow behavior of the PTFE can be controlled or prohibited, this is vitally important as there could be an undesirable discharge of the sealing material in the inner area. These circumstances are not to be underestimated; the difficulty to assemble to bodies of a two piece ball valve together. The connection has to be stringent actuated by gravity and on block. The smallest gap between the bodies would cause the stability of the ball valve to be significantly affected and the pre-load of the seat ring to be uncontrollable. This would result on the one hand in leakage or on the other hand in the locking of the ball. All of the above mentioned negative effects can be negated, and the sealing over an all side chambered PTFE profile ring is a highlight of the engineering of the armatures.

May 2013

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