Butterfly Valves
�2 ��
� cos �
β- Inclination angle of threads = 30 °, μ2- friction coefficient between threads.
Pi tan�
� � � d
α- Helix angle of threads
P i
- Bolt thread pitch do
� di d m
- Mean diameter = 2 d o
- Thread outer diameter
d i
- Thread inner diameter dm rm
1
�
2 T � F �r � �3 2 a m2 r m2
- Bolt head mean radius µ 3- Friction coefficient between bolt head and retainer.
Experimental test
To validate the method, a test was performed on different sized butterfly valves equipped with a rubber seal with 70 Shore A. The radial expansion of the rubber due to bolts compression on it was measured by a Vernier Caliper. The valves were subjected to a pressure
m
of 16 bar, and the sealing performance was observed at calculated torque values. The study found that:
• The valve sealed effectively with no leakage
• The acting torque to open and close the valve is acceptable
• Figure 6 shows the difference between experimental radial expansion of the rubber seal and the calculated radial expansion due to same tightening torque values of seal bolts
These results supported the calculated torque values, confirming that the mathematical method can help in defining safe and effective tightening guidelines during valve design or assembly.
Summary
This study presents a practical approach to determining the optimal tightening torque for butterfly valve rubber seals. The goal was to ensure a reliable seal without over-compressing the rubber, which can lead to premature wear and failure. By analysing the required expansion of the rubber seal to generate sufficient contact pressure, and translating that into the corresponding compression force and tightening torque, a safe torque range was established.
References Al-Ghathian, 1Faisal M. M. and 2Tarawneh, Muafag S.( 2005).“ Friction Forces in O-ring Sealing.” American Journal of Applied Sciences, 2( 3).
Werencke, W. P.,( 1987).“ Analysis of the reciprocating sealing process”. 11th Intl. Conf. On Fluid Sealing. Cannes, France.
Johannesson, H. and E. Kassfeldt,( 1989).“ Calculation of pressure distribution in an arbitrary elastomeric seal contact”. Wear, 130: 3-15.
About the author Ahmed Obaid is a Mechanical Design Engineer at Sierra for Engineering and Manufacturing, an innovative valve manufacturing company where he applies his studies. With extensive experience in valve and gearbox design, casting and manufacturing, he specialises in designing high-performance butterfly valves, check valves and plug valves according to AWWA and EN standards. His achievements include conducting advanced studies on sealing rubber behaviour to enhance product durability.
Certified with ISO9001:2015, ISO14001:2015, ISO45001:2018, CE, PED, SIL3, ATEX
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