Regarding bellows packing seals
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Are valves with bellows-sealed packing now required for substances with high toxicity or above? Manual valves and straight-stroke pneumatic valves are not a problem, but what about cut-off ball valves? They are all of angular stroke type; replacing them with linear stroke cut-off valves would result in excessive cost increases. Is there any standard stating that cut-off valves meeting GB/T4213 standards can be used with highly toxic media? The expert asked for bellows; I was a bit confused
The experts seem to be putting the focus in the wrong place; the purpose of using angle valves is to prevent erosion, while sealing performance is secondary in this context, and it can be addressed through other methods.
This post was last edited by jgc9992001 on 2021-10-26 09:40. Experts sometimes can’t say anything. Clause 10.1.2.4 e of the Specification for the Selection of Petrochemical Instruments 3005 states that diaphragm-sealed control valves are suitable for use with highly toxic media. Chemical Industry Standard 20507 11.5.3: In applications involving highly toxic fluids, fluids that must not leak, and rare or precious metal fluids, straight-stroke control valves with diaphragm seals should be used. They are all related to control valves
However, Standard 3005 also specifies the requirements for valve covers and gaskets that apply to control valves for these on/off valves, which seems a bit excessive. It isn’t clearly stated whether these on/off valves are of straight-stroke type; on/off valves of angular-stroke type do not have bellows. According to Standard 3005, bellows must be used for substances classified as highly toxic or more, and I recall that the standards state that bellows should be employed for such highly toxic substances. Ah, **if the drafting of standards isn’t thorough, it will cause great difficulties for businesses**
For ball valves used to control highly toxic media, there are requirements regarding the packing seal rating; a diaphragm seal is only used when the globe valve is employed as a control valve
This problem does exist; as pointed out by a fellow resident upstairs, the fundamental issue is that the standards were not formulated with a comprehensive consideration of all aspects, which led experts to make mistaken judgments.
It also depends on which standard your project follows
The bellows globe valve is in use; an additional seal has been added to ensure reliability；