INDUSTRY APPLICATIONS
INDUSTRY APPLICATIONS
Leakage failure analysis of the sanitary butterfly valve at the top of the tank
Operating Conditions:
1. Valve Installation Location: Tank top inlet, vertical pipe, long straight pipe extending upwards to the roof;
2. Valve Usage: Pneumatic single-acting normally closed butterfly valve, used for on/off operation; opens for water filling, closes for shutoff;
Fault Problem: Leakage at the valve stem.
Fault Analysis:
1. The closing time of the DN100 normally closed sanitary butterfly valve is within 1 second. Due to vertical installation and a long straight pipe above the valve, a significant water hammer effect is generated during the instant of closure.
2. As shown in the figure, force analysis of the valve on site:
The combined downward water hammer force and media force act on the upper surface of the butterfly plate, inevitably causing greater stress on the lower valve seat and bushing (area in red box in the image). Coupled with wear during the on/off process, uneven valve stem sealing will form over time (insufficient valve stem sealing at the top, excessive sealing at the bottom). Combined with water hammer impact, this ultimately leads to media leakage during valve closure.
3. The DN100 butterfly valve brackets currently used at this location are all conventional single-sided brackets. In vertical pipe installations, the valve stem also bears part of the actuator's weight, which is also an unfavorable factor.
4. In the storage process of normally closed sanitary butterfly valves, the valve seat under long-term pressure in the closed position and the aging of the rubber valve seat in the air will also affect the service life.
Solution:
I. The best solution is to replace the valve at the tank top location with a sanitary ball valve. Advantages of ball valves:
1. Improved valve pressure resistance (ball valve design pressure is 16 bar, butterfly valve is only 10 bar);
2. Sanitary ball valves can avoid the impact of water hammer on the valve stem during valve closure, ensuring reliable sealing and preventing leakage.
3. The valve stem sealing of sanitary ball valves is of the packing gland type. After prolonged use, insufficient packing seal due to normal wear can be tightened online, facilitating maintenance.
II. For some valves in use, due to the different structural lengths of ball valves and butterfly valves, they cannot be replaced without modifying the pipeline. Only structural or operational optimization is possible, as follows:
1. Change the single-sided bracket of the butterfly valve to a fixed bracket or double-sided bracket to offset the weight of the actuator and support the valve stem to some extent, improving the uneven valve stem sealing.
2. Add throttle valves to the cylinder air intake and exhaust to control the air intake and exhaust speed, increase the valve closing time, and reduce the water hammer effect caused by rapid closure.
3. If there are other manual or automatic valves upstream of the butterfly valve, try to see if they can be linked with this valve; open the tank top valve first when opening and close the upstream valve first when closing.
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