What are the valve types H, F, and Y? What are the meanings of these 3 letters?

What are the valve types H, F, and Y? What are the meanings of these 3 letters?

Please refer to "JB/T308-2004 valve model preparation method"Sealing surface material codeH Cr13 stainless steelF fluoroplasticY cemented carbide

Please refer to "JB/T308-2004 valve model preparation method"Sealing surface material codeH Cr13 stainless steelF fluoroplasticY cemented carbide

Please refer to "JB/T308-2004 valve model preparation method"Sealing surface material codeH Cr13 stainless steelF fluoroplasticY cemented carbide