Level/Pressure Instrument connection to be provide block valve in between

[silebi66]

Dear eng-tips member:

Sorry for bother you this trivia.

I am confused why the Level/Pressure Instrument connection to be provide block valve in between

Equipment nozzle and instrument tip point. (Pls see the attached)

Is it for maintenance issue or other reason? Why is the ball valve for the Temperature / Flow instrument usually not shown in the P&ID ?

Thank you very much for your help.

 

[DRWeig]

It's so you can change a failed instrument without shutting down the process.

Often it is not just a single block valve. Double block and bleed arrangements are needed when the fluid is dangerous or under high pressure.

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

 

[controlnovice]

Temperature elements general don't have valves between them and the process because they are inserted INTO the process. If the process is dangerous, a thermowell is used. If it is benign (water, air, etc) or the process does not have to be stopped for repairs, sometimes the thermowell is not used.

Flow elements don't have valves between them and the process because they are inserted INTO the process. You will have valves and bleeders up and downstream of the flow element to remove it if it fails, and those should be shown on the P&ID.

______________________________________________________________________________
This is normally the space where people post something insightful.