Insufficient understanding of the two-way sealing mechanism of triple-eccentric butterfly valves

Firstly, bidirectional sealing means that the valve can provide isolation and sealing, regardless of whether the medium flows from left to right or from right to left. Secondly, the three-eccentric butterfly valve is capable of providing two-way sealing; I’m not quite sure about the exact principle behind this, so I’ll wait for the experts here to answer.

To understand the sealing principle of the triple-eccentric butterfly valve, one must first understand its structure. 1. The triple-eccentric butterfly valve is a type of eccentric butterfly valve (as opposed to the centerline butterfly valve); it corresponds to Class B butterfly valves as defined in API 609 (Class A being the centerline type). The structural diagram of the triple-eccentric butterfly valve is as follows: 2. The triple-eccentric butterfly valve comes in two types of sealing arrangements – one is pure metal sealing, and the other is a multi-layered combination sealing using metal and graphite. Due to its better elasticity, the multi-layer composite seal of metal + graphite offers superior sealing performance compared to pure metal seals, enabling zero leakage. The two sealing types are shown in the figure below: 3. When a triple-eccentric butterfly valve is sealed in the forward direction (along the flow direction of the medium), in addition to the force exerted by the butterfly plate on the valve seat, there is also the force exerted by the medium itself; as a result, the sealing effect is very good, with virtually no leakage occurring. In reverse sealing (against the flow direction of the medium), the butterfly valve disc must first overcome the force exerted by the medium before it can press against the valve seat for sealing; essentially, it is the force applied to the butterfly valve disc by the valve stem that causes it to press against the valve seat for sealing, which constitutes forced sealing. Therefore, eccentric butterfly valves generally have a preferred flow direction for the medium; typically, the sealing pressure in the reverse direction is lower than that in the preferred direction. When operational conditions require flow in the reverse direction, the purchaser must specify this reverse pressure in the order. At present, among domestic triple-eccentric butterfly valves, only the products of a few manufacturers can achieve zero leakage at full pressure in reverse flow.

Thank you for your detailed reply. In reverse sealing (against the flow direction of the medium), the butterfly valve disc must first overcome the force exerted by the medium before it can press against the valve seat for sealing; essentially, it is the force applied to the butterfly valve disc by the valve stem that causes it to press against the valve seat for sealing, which constitutes forced sealing. The requirements for the valve stem in this case must be quite high; currently, the material used for the valve stems of our low-temperature butterfly valves is XM-19. Please take a look at the attached image to see if reverse sealing can be achieved Pictures online

Indeed, higher requirements are placed on the valve stem during reverse sealing. In addition to considering the strength of the valve stem, stiffness should also be taken into account, that is, the deformation should be minimal. Additionally, for triple-eccentric butterfly valves, the torque on the valve stem is relatively higher, but the diameter of the valve stem cannot be made too large. It is necessary to take into account various factors such as materials and structure. XM-19 (S20910) is a nitrogen-enhanced austenitic stainless steel; although it has higher strength compared to ordinary austenitic stainless steels such as 316, stress analysis is still required. Also, the diagram you sent is a structural diagram; based solely on it, it’s not possible to determine whether reverse sealing can be achieved.

Thank you for your reply. Happy May Day!

Can this be sealed in reverse? How is it determined whether reverse sealing is possible?

This post was last edited by Liu Jiajia on 2019-4-30 at 16:10. Sealing and leakage are relative concepts; you have a misunderstanding. Pay attention to what I’ve said. Therefore, eccentric butterfly valves generally have a preferred flow direction for the medium; typically, the sealing pressure in the reverse direction is lower than that in the preferred direction. When operational conditions require flow in the reverse direction, the purchaser must specify this reverse pressure in the order. At present, among domestic triple-eccentric butterfly valves, only the products of a few manufacturers can achieve zero leakage at full pressure in reverse flow. In other words, it may not be possible to achieve zero leakage at full pressure in reverse mode.