×
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

NPSHA

NPSHA

(OP)
I have a question that I need a simple answer to.

We have a cooling system that has flows up to 75usgpm.  The pressure drop through this system is taken at 30ft of head.  This cooling system has an expansion tank that branches straight up about ~10ft abouve the pump and it is open to atmosphere.  This branch to the exp. tank is located about a foot upstream of the pump inlet.

When I am calculating NPSHA do I add the atmospheric pressure since the tank is open?

I have searched this site and read quite a few useful threads.  I think that I should add the atmospheric pressure but I would like someone to confirm this.

RE: NPSHA

For an open system on the inlet side normally called a flooded system use:-

NPSHa= Ha - Hvpa + Hst - Hs

Ha = absolute pres.in ft of liquid acting on the supply level - at sea level use 34ft

Hvpa = vapour pressure in ft at the pumping temp. assuming standard of 65 - 70 F. Hvpa allow 0.8

Hst = static head in ft above the centre of the impeller - 10 ft as per your post

Hs = all losses in ft for the inlet configuration - ie, pipe work, valves and fittings - assume 3 ft or your calculated figure

For a simple installation like yours  

NPSHa calc. is 34 - 0.8 + 10 - 3 = 40.2 ft

RE: NPSHA

(OP)
Artisi,

Thank you very much.

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