How does a balanced bellows safety valve balance the back pressure?
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How does the bellows of a safety valve balance the back pressure? Is it through the contracting force of the bellows acting on the valve seat? Is it still the shape of the ripples that helps to cancel out the back pressure up and down?
There is a limit to the extent to which balanced safety valves are unaffected by back pressure. According to the standards, the balanced type can be used when the back pressure of the safety valve is greater than 10% of the set pressure and less than 50% of the set pressure. Since a balanced safety valve has a diaphragm, there are two aspects to the diaphragm’s role in balancing the back pressure. First, it occupies the longitudinal acting surface, preventing longitudinal forces from acting on the sealing components. Second, the bellows eliminates the back pressure coming from the outlet through its own deformation, so that this back pressure does not affect the proper operation of the safety valve. Therefore, the balanced safety valve is not affected by back pressure.