Valve Design in Vacuum Condition?

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The valve vendor will not know what your operating conditions are unless you provide the information. For a vacuum condition, some valve stem seal chevrons might be turned the opposite direction than for pressure service (concave side toward greater pressure).

Nornally single datasheet covers all size valves say 1" - 16" and it is very difficult to provide indivaidual valve operating conditions.

That is why you need to tell prospective vendors what your conditions are. If you have not done so already, then proceed accordingly.

Thanks.

If you've passed the valve datashset details to the vendor, you've already told him the vacuum level - full vacuum. But apart from what Tornado said in #1, I'd be surprised if full vacuum were a limiting condition for valve design.