TECH TALK sure locking . Also , periodic opening of the valve during significant changes of pressure or temperature is appropriate . This may be unacceptable in some isolation valve applications .
C ) Design Features . An engineered control , in the form of a feature designed into the gate valve , to prevent pressure locking is often the preferred method to address the issue . There are a variety of engineered solutions available including the following :
• A small hole may be provided in the upstream side of the gate , permitting the cavity to equalize with the upstream side . This is a simple solution and considered the most economical ; however , it renders the gate valve a unidirectional valve which may limit installation options or conflict with the application .
• A hole in the seat or body bridge wall on the upstream side . This may be referred to as an internal equalizer . Like the hole in the gate , this also comes at the cost of making the gate valve a unidirectional valve .
• A pipe connecting the body cavity beneath the bonnet to the body on the upstream side . This is referred to as an external equalizer and may be provided with a valve to maintain bi-directional operation of the valve .
• Install a pressure relief valve to the cavity beneath the bonnet to automatically relieve the cavity pressure . This needs to be connected to a safe discharge point .
• Install a manual vent valve in the bonnet to manually relieve pressure . Again , this needs to be connected to a safe discharge point .
• An automatic center cavity equalization valve ( ACCEV ). The ACCEV piping connects the center cavity to both the upstream and downstream sides of the valve via a special ball check valve to permit automatic operation , including relieving the center cavity to the downstream side in situations where that side is at the higher pressure .
Several of these features are illustrated in Figure 2 . Any one feature should do ; there is no need for multiple features to address the issue .
Although there is no ideal answer to the problem of pressure locking in gate valves , there is a large variety of solutions from which to select . The specific application of the valve needs to be considered when choosing the best approach .
REFERENCES
1 . J . K . Wang , M . S . Kalsi , and S . S . Averitt . Development of a Validated Pressure Locking Methodology for Gate Valves .
ABOUT THE AUTHOR
Randall Elmore is an alumnus of Virgina Tech . He is currently an Order Engineering SME at Flowserve ’ s Raleigh , NC plant . Where he has spent the last 19 years working with gate , globe , and check valves . www . valve-world-americas . net • October 2024 | Valve World Americas 31