For my fluid service of fuel gas (design conditions, temp 100 deg C and pr- 5.0kg/sq sm) and sour water acid gas (temp 160 deg C and pr- 5.0 kg/sq cm), I am told to use Plug Valves. But I am confused between soft seated/ metal seated plug valves.Can anyone pls suggest what should be the design basis for selection and also which of the two are preffered, their advantages and limitations."Lubricated" plug valves are all metal. They use a sealant that is injected under pressure to seal and lubricate the plug. The sealant is formulated to be compatible with and noncontaminting for the specific process fluid in the valve. Lubricated plug valve are usually manual because they are complicated to automate. It's necessary to activate the lubricator before turning the valve, and most automation does not have that functionality. "Nonlubricated" plug valves have the plug running in a TFE sleeve usually, but other polymers may be used. In this configuration they may be cast in exotic alloys for corrosion resistance. No additional lubrication is required. A variation is the fully-lined plug valve that has a TFE lining and a PFA encapsulated plug. That lets the user run corrosive chemicals through a valve with a ductile iron body because the body never gets wet-just the (chemically inert) TFE liner.

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