how to put a PSV in service

[edanyel]

I don't know, maybe it's a silly question but...
Please, look at the picture, if I have to put the PSVb in service, which will be the correct sequence?
Open BVb1 first, then BVb2 ?
Open BVb2 first, then BVb1 ?
It doesn't matter which one first ?
For any answer please, could you give me your technical or safety arguments?
Does any standard say anything about that?
Thanks in advance
Daniel

 

[Latexman]

What's the situation? A start-up of a new tank? Switching from PSVa to PSVb while the tank is in service? Start-up after tank maintenance?

Good luck,
Latexman

 

[edanyel]

In this case, Option b - Switching from PSVa to PSVb while the tank is in service, but the situation shouldn't make any difference.
I think the correct way is -in any case-
Open BVb2 first, then BVb1. Am I wrong?
My reason is -for safety-, you first have your PSVb discharge open, then the inlet, then you're allowed to close the PSVa.
I'd like to hear opinions.
thank you
Daniel

 

[BenThayer]

daniel,

you have it right. open the discharge first and then open the inlet.

depending on design, many PSV's have different ratings on the inlet flange than the outlet. it is not uncommon to have a Class 300 flange on the inlet and Class 150 on the outlet.

in the unlikely circumstance that someone becomes distracted or called away in the midst of making the switch-over, you don't want a 500 psig service open on the inlet and closed on the outlet. if the PSV leaks just a bit, you will over-pressure the outlet flange.

but when switching the other valve out of service, you isolate the inlet and then the respective outlet.

so open outlet, open inlet, close inlet and close outlet.

 

[olcrazy1]

this is why they make change over valves to put before and after the relieve valves. if you go your method you need to have a clear process in place so that an operator dose notmake an error. Also you need to find a way to lock the ball vaves out so that no one can open or close by mistake, I believe this is a code requirment.

 

[itascot]

Hello, looking at your picture & reading through the answers; I would suggest you look at this link

http://www.tycoflowcontrol-na.com/ld/ANGMC-0241-US.pdf

As olcrazy1 writes. I believe it is a code requirements...safety is the important factor (not only for valve, but mostly for the workers), take the possible error in closing, bleeding & reopening valves out of the equasion.
Ciao

 

[edanyel]

Hi you there!
You have all been very helpfulll.
I apreciatte your responses.
Keep it going!
Thank you!
Daniel