A good example is the bellows seal design, such as Badger's Type 808 bellows sealed globe valve. This is suitable for critical, zero-fugitive emission, high-purity or high-vacuum applications.
The bellows forms a flexible static seal that is leak-free, as long as the integrity of the bellows remains intact. However, should the valve fail, a set of back-up packing allows the valve to continue to operate safely until repairs can be made.
The valve is available in sizes ¼in, ½in, ¾in and 1in and standard features include interchangeable trim sets, bellows packing, PTFE CV ring back-up packing and PTFE bellows gasket.
A range of accessories is available, including positioners, filter regulators, gauges, I/P limit switches and solenoid valves.