×
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

Pressure Relief Valve Discharge Pipe Sizing

Pressure Relief Valve Discharge Pipe Sizing

Pressure Relief Valve Discharge Pipe Sizing

(OP)
I could use some guidance on sizing relief valve discharge pipes. I have an industrial waste water treatment plant that has 2 filter banks for final polishing of treated water before it is discharged. One bank treats 6,700 GPM and the other 3,300 GPM. The main influent lines have relief valves on them. The larger bank has a 10"x8" valve and the smaller has a 6"x8" valve.

Right now, the relief valve discharge lines just go a few feet out the wall and turn down to the ground. I have been asked to route the lines to a more suitable location for discharge, which is about 250' away. The friction losses and velocities in 10" pipe carrying 6,700 GPM and 8" pipe carrying 3,300 GPM are very large.

So, what is the proper way to size these lines? Is there a target velocity or friction loss I should shoot for? Also, can I combine the 2 into a single discharge header?

Thanks for your help

RE: Pressure Relief Valve Discharge Pipe Sizing

Water PSV's are not critical flow devices so they are not quite as touchy about downstream pressure as a gas PSV is. For that kind of problem you have to account for elevation changes (for discharge higher than inlet I use the hydrostatic head as my tail pressure, if the discharge is lower than the inlet then I ignore the elevation change), then I like to use a head pressure of about half of PSV set point and a tail pressure determined by elevation. Adjust pipe size until the head and tail pressures are in the ballpark. If you combine the two PSV into one line then use the combined flow for your pressure drop calculation. Darcy-Weisbach is probably your best bet for flow calcs.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

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