×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Back pressure 3 %/ outlet loss 10% guage or absolute

Back pressure 3 %/ outlet loss 10% guage or absolute

Back pressure 3 %/ outlet loss 10% guage or absolute

(OP)
We had a question recently on engineers using differnet methods to check the inlet losses on PSV's as a percent of set pressure. So.. what is the API measure

DP/ set pressure *100 = % loss
so is set pressure in absolute or guage ?

and the same for outlet losses..  

RE: Back pressure 3 %/ outlet loss 10% guage or absolute

Assuming steam flow protecting a Section VIII vessel, no fire-case:

3% inlet loss is a guide to prevent chattering and beating the seat/nozzle to premature death.  

3% of set pressure with a valve set at 150-pisg, max to design is 4.5 psig loss on inlet for the stamped capacity.  To me this is P1= 154.5 to P2= 150 (set) for loss determination

In my book this case now allows 5.5 psi on the discharge  for "meeting the interpretation" of the Code Appendixes, not required, recommended.

Remember the delta P is across the nozzle the calculation now becomes P1= 5.5 psi and P2=0,  the specific volume increases dramatically, as does the tail-pipe diameter.  This assures if I use the minimum diameter & maximum length I prevent the vessel from seeing more than a 10% OP as defined by Code.

 

RE: Back pressure 3 %/ outlet loss 10% guage or absolute

Gauge pressure (not absolute).

RE: Back pressure 3 %/ outlet loss 10% guage or absolute

For historical (not engineering or scientific) reasons, all psv calcs are in gauge pressure.  At really high pressures, this is a pretty small thing.  For low-pressure psv's it isn't trivial, but that's the way it is done.

David

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources