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!

*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.

Jobs

Flow in Pipe

NPSHa - Net Positive Suction Head available by itsmoked
Posted: 12 Jan 10 (Edited 16 Jan 10)


This FAQ is a reduction of tbarkerjr's question and BigInch's response on: 12 Jan 2010.

I found it to be clear, concise, and informative.

Thanks you two!

----------------------------------------


The only two that are important are NPSHa and NPSHr.  You don't calculate NPSHr, you get it from the mfgr's pump data. You only have to calculate NPSHa which must be >= NPSHr.

Use absolute pressures. (If tank is open or closed, it makes no difference to the equation, as long as you calculate the tank's absolute pressure correctly).  Vapor pressure is always absolute.

NPSHa = p(on_fluid_surface)/y - p(v)/y + v(s)^2/2g + h(e) - h(l)

Note: The velocity term can be ignored normally as it doesn't contribute significantly.

p(on_fluid_surface)absolute pressure on_fluid's_surface
y = specific weight of fluid
v(s) = velocity of fluid
g = acceleration of gravity
p(v) = vapor pressure
h(e) = elevation from surface to pump
h(l) = head loss


The sign convention for h(e) is positive when the fluid surface is above the pump and negative when below the pump's Center Line(CL).

Dropping the velocity term is common as it's almost always relatively small, not worth calculating, and yields a conservative result.



 

Back to Pipelines, Piping and Fluid Mechanics engineering FAQ Index
Back to Pipelines, Piping and Fluid Mechanics engineering Forum

My Archive


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close