Applications for globe valves: Part 5

9. Upper thread stem globe valve: The stem of this type of globe valve is not in direct contact with the working medium. According to the shell material, sealing pair material, packing material, valve stem material, suitable for different working conditions. If the valve body and bonnet material are carbon steel, the sealing pair material is alloy steel, the packing is flexible graphite, and the valve stem material is Cr13 series stainless steel, it is suitable for water, steam and oil pipelines; If the valve body and bonnet material is 12Cr18Ni9 or 06Cr19Ni10, the sealing pair material is the valve body itself material or cemented carbide, the packing is PTFE, and the valve stem material is 14Cr17Ni2, which is suitable for nitric acid-based corrosive medium pipelines or devices; If the bonnet material of the valve body is 06Cr17Ni12Mo2Ti, the sealing sub-material is the material of the valve body itself or cemented carbide, the packing is PTFE, and the stem material is 14Cr18Ni11Si4AlTi, it is suitable for acetic acid-based corrosive media pipelines or devices. However, the maximum nominal size of this type of globe valve is DN200, and the globe valve above DN200 should be equipped with a bypass valve or a bypass structure in the upper device. Generally the inlet end ≥ DN200 globe valve is above the disc, that is, high in and low out, this is to prevent too much effort and too thick stem when closing.

10. Lower thread stem globe valve: The stem thread of this type of globe valve is directly in contact with the working medium and is directly eroded by the medium, which makes the stem thread easy to rust and cause laborious opening and closing. The nominal size of the globe valve of this structure is relatively small, generally between DN6 ~ DN50, and most of them are used in instrument valves and sampling valves.

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