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Vervo forged steel valve
From:net    Date:2008-12-26
Bolt Bonnet :The body flange and bonnet flange are joined by studs and nuts,with a gasket of suitable design/material inserted between the flange faces to facilitate sealing.Studs/nuts/bolts are tightened to prescribed torques in a pattern defined by the manufacturer to affect optimal sealing.However,as system pressure increases,the potential for leakage through the body/bonnet joint also increases.

Pressure Seals:Most pressure seal designs incorporate “bonnet take-up bolts”to pull the bonnet up and seal against the pressure seal gasket.This in turn creates a seal between the gasket and the inner(I.D.) of the valve body.A segmented trust ring maintains the load.The beauty of the pressure seal design is that as system pressure builds,so does the load on the bonnet and correspondingly, the pressure seal gasket.Therefore,in pressure seal valves,as system pressure increase,the potential for leakage through the body/bonnet joint decreases.
This design approach has distinct advantages over BBV in main steam,feedwater,turbine bypass,and other plant systems requiring valves that can handle the challenges inherent in high pressure and temperature applications.However,due to its reliance on system pressure to aid in sealing,pressure seal valves are best applied in system where the minimum,consistent operating pressure is in excess of 500psi.
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