Can centerline butterfly valves be made with a hard seal?
Thread Content
From what we have learned before, a hard-sealed valve is an eccentric valve, and it is difficult to line such eccentric valves. So why can’t centerline butterfly valves be made as hard-sealed valves?
First of all, I would like to thank the original poster for their post. Next, let me introduce myself: our company specializes in special alloys, and for industries such as valves and pumps, we can provide the corresponding raw materials. The main materials include Hastelloy, Monel alloy, Inconel alloy, super duplex steel, etc. We also offer forged parts, cast raw materials, as well as various welding materials used in these industries. I hope that the experienced professionals here will give us a chance to work together. Thank you. My WeChat number is 15962090804
A standard center butterfly valve achieves sealing through the deformation of the sealing material between the valve disc and the valve body; without such sealing material, a gap exists between the valve disc and the valve body (otherwise it would not be possible to rotate), and thus sealing cannot be ensured. It’s possible to achieve extremely high machining precision, but the cost would soar and it wouldn’t be practical. A triple-eccentric butterfly valve achieves sealing through the seal formed between the valve disc and the valve seat, similar to a lid or plug creating a seal with the valve seat, with a gap existing between it and the valve body. Overall, it is the different structure that prevents the center butterfly valve from achieving a tight seal. To be precise, center butterfly valves also have a hard seal, although the leakage rate cannot be guaranteed.
The sealing performance of center-line butterfly valves is the worst; if one chooses a center-line butterfly valve, why choose a hard-seal version?
Well, in theory, center butterfly valves can also achieve a hard seal, but the actual performance is not satisfactory; therefore, people generally do not choose them when making selections. Can an eccentric butterfly valve be lined? It is possible to do so, but after lining, it tends to come off during operation.
Generally, when choosing centerline butterfly valves, soft seals are used; for hard seals, eccentric butterfly valves are preferred. Since I work in the sewage sector and don’t have much knowledge about valve equipment, I’d like to learn more about it :)
Conventional butterfly valves use soft seals along their center line, while hard-sealed butterfly valves have an eccentric design. When it comes to hard-sealed centerline butterfly valves, they are essentially air valves that cannot provide proper sealing
For better performance, it’s better to choose the eccentric type. Longer service life: With linear valves, when they rotate (from closed to open), there is no immediate separation from the valve seat, so over time either the valve cannot be opened or there will be some leakage due to wear. In the case of eccentric-type valves, when they rotate, the valve element comes apart from the valve seat momentarily, resulting in no wear; as a result, their service life is longer. Additionally, the torque required to operate them is relatively low. Good functionality: Eccentric valves generally come with indicated recommended installation directions, as proper installation ensures better sealing performance as the pressure in the pipeline increases. Eccentric valves allow for the replacement of the valve seat relatively easily without the need to remove the central shaft.
Since our medium is ozone-containing wastewater that is corrosive, if an eccentric butterfly valve is used without a stainless-steel construction, could it be lined with PTFE?
Mm-hm, I chose it in the same way before
Is tetrafluoro equivalent to PTFE? If so, it is not recommended. If the fluid is corrosive, PTFE will not hold up for long, and if the corrosion is not complete, leaks may occur. If reinforcement is needed, electroplating (with Cr) on the valve disc or seat can be performed, or the material could be changed to something like A890 or Cr.5A, which would be more effective.