The structure, advantages and disadvantages of sealing butterfly valve

Sealed butterfly valves have metal-to-metal hard seals and metal-to-rubber or plastic soft seals. The sealing ring can be placed on the butterfly plate or on the valve body. Below are several typical sealed butterfly valve structures. According to the position of the butterfly plate in the valve, the butterfly valve can be made into center symmetrical, offset (single eccentric, double eccentric and triple eccentric) or inclined.

1. Centerline Butterfly Valve

The central line of the butterfly valve stem axis and the central plane of the butterfly plate are in the same plane and perpendicular to the center line of the valve body pipeline, and the areas on both sides of the butterfly plate are symmetrical to the stem axis. The centerline butterfly valve is generally made of rubber-lined form. Due to its simple structure, small flow resistance and small switching torque, it is widely used in medium and small butterfly valves.

2. Single eccentric butterfly valve

In the single eccentric butterfly valve, the valve shaft deviates from the center plane of the disc, resulting in a primary eccentricity, so that the upper and lower ends of the disc close to the valve shaft no longer become the axis of rotation, eliminating the friction and wear of the upper and lower shaft ends and causing leakage. The sealing effect is better, but the sealing effect in the two directions is inconsistent. Generally, the forward direction (flow from the valve shaft to the sealing surface) is easy to seal, and the reverse direction is easy to leak because there is no supporting effect of the sealing surface. However, the use of rubber soft seal, using its elasticity, can well achieve two-way sealing. Since its sealing contact mechanism belongs to "ball in cone", there are always two points of the disc that cannot be out of contact at each opening. When used for adjustment, these two points will wear more than other parts, and the seal will be damaged. adversely affect. If it is made of metal hard seal and the two positive cones cooperate, when the butterfly plate is rotated, the sealing surface will interfere, and it will be difficult to switch.

3. Double eccentric butterfly valve

Double eccentric butterfly valve, in order to improve the situation of single eccentricity, the valve shaft is offset by a distance, so that the connection line between the shaft center and the sealing point and the sealing surface form an obtuse angle, so that there is no interference during sealing, and the tighter it is, the tighter it is. Greater seal face pressing force. The feature of double eccentric is that when the valve is opened, the sealing surface of the disc can be quickly separated from the valve seat, the contact and scratching effect is greatly reduced, and it can be made into a metal sealing valve.

4. Triple eccentric butterfly valve

The triple eccentric butterfly valve is to rotate the positive cone angle by an angle and change it to the inclined cone angle, so that the eccentricity can be reduced, and the opening torque is also reduced.