What are the differences between three-offset butterfly valves, double-offset butterfly valves, single-offset butterfly valves, and center-line butterfly valves?

These types of butterfly valves, including center-line, single-offset, double-offset, and triple-offset butterfly valves, change their sealing and opening states by adjusting the position of the valve disc's rotating shaft.

Under the same conditions, the angle required for the valve disc to separate from the seal when opening is smaller for each type, and the torque at each valve opening is greater for each type.

Triple-offset butterfly valves: For high-temperature resistance, hard sealing must be used, but leakage is high; for zero leakage, soft sealing must be used, but it is not resistant to high temperatures. To overcome this contradiction of double-offset butterfly valves, a third offset was added to the butterfly valve. The so-called third offset is that the shape of the sealing surface is not a regular cone but an oblique cone. The unique feature of the triple-offset butterfly valve is that the valve on which the butterfly plate is installed is a three-segment shaft structure. The two shaft segments of this three-segment shaft stem are concentric, while the center line of the center shaft is offset from the two end axes by a center distance, and the butterfly plate is installed on the middle shaft segment. This eccentric structure makes the butterfly plate a double-offset state when it is fully open, and a single-offset state when the butterfly plate rotates to the closed position. Due to the action of the eccentric shaft, when approaching closure, it moves inward towards the sealing conical surface of the valve seat by a distance, and the sealing surfaces of the butterfly plate and valve seat match.

Double-offset butterfly valves: Further improved from single-offset butterfly valves, these are currently the most widely used. Its structural features are that the valve stem axis is offset from both the butterfly plate center and the valve body center. The effect of the double offset allows the butterfly plate to quickly separate from the valve seat after opening, greatly eliminating unnecessary excessive pressure and scratching between the butterfly plate and the valve seat, reducing opening resistance, reducing wear, and increasing the life of the valve seat.

Single-offset butterfly valves: To solve the problem of the butterfly plate and valve seat being squeezed in concentric butterfly valves, the single-offset butterfly valve was produced. The structural feature is that the valve stem axis is offset from the center of the butterfly plate, so that the upper and lower ends of the butterfly plate are no longer the center of rotation, distributing and reducing the excessive pressure between the upper and lower ends of the butterfly plate and the valve seat.

The center-line butterfly valve is characterized by the valve stem axis, butterfly plate center, and valve body center being in the same position. Because the butterfly plate and valve seat are always in a state of squeezing and scratching, the resistance is high, and the wear is fast. The structure is simple and convenient. To overcome squeezing and scratching and ensure sealing performance, the valve seat basically uses elastic materials such as rubber or polytetrafluoroethylene.