To buy a gate valve with high rating (1500LB) and our client has bben commented us taht this valve should have following condition:
1- Overpressure protection
2- Equalizing valve
3- parallel disk
With high pressure and temperature valves a method should be used that will prevent the gate valve bonnent area from be overpressurized from fluid being trapped in the neck and thremal increase that can cause fluid expansion.  This can lead to a very danerious condition.  What could happen?  The gate or wedge can be locked in the closed position preventing the valve from being opened to worst case the pressure can rise above the allowable deign limit for the material until a failure of the shell occurs.  There are many ways of providing the protection - from the very simple to very complex.  Keep in mind the more complex the more chances of it not working are.

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