Selection Principles of Ball Valves’ Ball Types (Part Two)

The hemispherical and v-shaped ball
The purpose of using the hemispherical ball for the ball valve is to reduce the weight of the ball as the internal part, so as to achieve the purpose of reducing the price of the ball valve. Hemispherical balls are typically combined with eccentric type balls to form the desired shut-off seal pressure. Hemispherical ball valves are mainly used for the medium pipelines in mines.

The application of the v-shaped ball is similar to that of the hemispherical ball. If a hemispherical or v-shaped ball valve is required, it should be indicated in the valve data sheet and it should be confirmed that the manufacturer's design and production of such valves are mature.

The eccentric ball
The eccentric ball uses the eccentric butterfly valve sealing principle, that is the cam effect, to form the required shut-off seal pressure and to reduce or avoid the wear of the internal parts and the valve seats. Different from the fixed ball, the eccentric ball produces the seal pressure by the torque of the valve stem. The three eccentric structure of the the eccentric ball can avoid the wear of the internal parts and the valve seats, which makes the eccentric ball valve have better performance than the trunnion ball valve. But if the eccentricity is not set incorrectly, the performance of the valve may be reduced.

If a eccentric ball is required, it should be indicated in the valve data sheet and it should be confirmed that the manufacturer's design and production of such valves are mature.

The orbit type ball
The orbit type ball uses the orbitstructure of the valve stem to make the orbit valve move up and down in the opening and closing process, and uses the wedge-shaped structure formed by the end of the stem and the ball to make the ball pressed or away from the valve so as to form the required seal pressure, or to relieve the seal pressure. If we continue to rotate the hand wheel, the ball will begin to rotate, and eventually achieve the purpose of cutting off or connecting the media in the pipes. As the ball has no contact with the valve seat in the rotation process, there will be no wear between the valve seat sealing surface and the spool (ball) sealing surface. Therefore, the orbit valve has better performance than the trunnion ball valve, and is more suitable for the metal hard seal. But the orbit valve is often used combined with the top-mounted valve body, and it has the disadvantages of being heavy due to the heavy top-mounted valve body and being expensive. It is also difficult to process the orbit on the valve stem. If the design and processing of the orbit is not appropriate, it will lead to the deterioration of valve performance.

If the orbit valve is required, it should be indicated in the valve data sheet and it should be confirmed that the manufacturer's design and production of such valves are mature.