INDUSTRY APPLICATIONS
INDUSTRY APPLICATIONS
VI-level sealed regulating valve solution
I. Project Requirements: GLOBE pneumatic diaphragm bellows control valve, on-off characteristic, DN100-CL150, medium hydrogen cyanide/N2, temperature: 15℃, pressure 100 mmH2Og.
II. Project Challenges:
The customer chose the GLOBE control valve type for on-off use, with a handwheel and bellows, and must ensure VI-level sealing. However, our conventional control valves have IV-level sealing. Achieving VI-level sealing for a DN100 control valve, which has a larger diameter, is challenging. If a common pneumatic bellows globe valve is selected, sourcing the diaphragm cylinder, handwheel, and bellows is difficult. Therefore, the customer's needs must be met by improving the sealing performance of the GLOBE control valve.
IV. Solutions
Three solutions were provided to the customer for achieving VI-level sealing with the Globe control valve.
1. Change the valve seat seal to a PTFE soft seal structure.
This soft seal structure can achieve essentially zero leakage and meet customer requirements. However, considering the wear resistance of the valve sealing pair and the possibility of medium residue inside the valve stem, the customer abandoned the soft seal solution.
2. Double valve stem metal seal structure: In this solution, the pilot valve stem plays the main role in pressure bearing and pressure release. Due to the small cross-sectional area of the pilot valve stem, good sealing performance can be ensured, thereby reducing the pressure on the main valve seat and enabling the main valve seat to achieve good sealing performance to meet customer requirements. However, considering that the internal components of this valve type are relatively complex and the medium hydrogen cyanide is highly toxic, making residue in the valve stem easy, the customer abandoned this solution.
3. Unbalanced single-seat metal hard seal structure:
For the unbalanced single-seat structure, two points need to be noted during manufacturing: First, the valve stem and valve seat sealing surfaces must be precisely ground to achieve a surface finish with zero leakage; second, since it is an unbalanced valve stem, if it is low-inlet high-outlet, the unbalanced force is too large, which is not conducive to sealing. Therefore, this valve should be changed to high-inlet low-outlet during use, which is conducive to sealing, and the higher the working pressure, the greater the sealing force. The customer ultimately chose this solution.
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