When discharging storage tanks on (petro-) chemical plants there is often a hazard of mixing two or more chemicals by forgetting to close a discharge valve before opening another. This can lead to product degradation or more serious, this can lead to dangerous chemical reactions.
During normal operation only one tank should be opened at the same time.
To prevent opening more than one valve at the same time a valve interlock can be installed on each individual valve leaving them all locked closed to be operated with the same key. This key can be stored in a key cabinet in the control room.
- option 2 bolt lock
All 3 valves V1, V2 and V3 are locked closed with key A in the control room.
Take key A from the control room and select one of the tanks to be opened.
If selected for example tank 2, insert key A in the valve V2. Unlock the closed position of the valve and open the valve. Take out key C and return to the key cabinet with this key. Valve V2 is now locked open and valve V1 and V3 remain locked closed.
Once the valve V2 is open the key A will be trapped consequently key A cannot be used to open tank 1 or 3.
To select another tank take key C from the key cabinet unlock and close valve V2.
Take out key A from valve V2. Now all valve locks are locked closed again and you can make a new selection.
Depending on which key is stored in the key cabinet you have an overview of each status of the valves. For example if key C is in the key cabinet valve V2 is locked open and all other valves are locked closed.