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

How to determine NPSHa for two pump in parallel

How to determine NPSHa for two pump in parallel

How to determine NPSHa for two pump in parallel

Hi, Can you please advise on how to calculate the head losses for two centrifugal pump connected in parallel to a common suction line? And also the NPSHa for the pump. The flow rate require is 500 liters/sec and the pump is 100m away from a reservior 5 m above the pump. The water is pump to two tanks one 200m away at 30m and the other 300m away at 50m. Currently the selected suction pipe size is 500mm. Thanks.


RE: How to determine NPSHa for two pump in parallel

Assuming both parallel pumps are identical, you calculate normally to find the absolute pressure at the pump suctions, using the actual flow in the common line and then dividing the flow as it physically does, calculating losses in each branch to find the suction pressure available at each pump suction.  They are unlikely to be equal, and even if they are, it would be wise to use 60% flow in each branch, even though you expect closer to 50%, as the pumps and impellers are NEVER identical, and the flow will be slightly higher on one.  You just don't know which one it will be.

Remember that the NPSHr is more critical with a single boiling point fluid (like water) than it is with a multi-boiling point fluid (like oil), as cavitation will come on very quickly with single boiling point fluids, and slowly with multi boiling point fluids.

RE: How to determine NPSHa for two pump in parallel

Is those two pumps are running concurently or as a standby operation (one running, and one standby?, 2 x 100 %).

If the later is the case, line suction line size need to be sized for both pumps are running, ie suction line need to be sized for 1000 l/s (1 m3/s). And the pressure drop shall be sized accordingly.


Senior Process Engineer
Kuala Lumpur, Malaysia

RE: How to determine NPSHa for two pump in parallel

Suggest you invest in AFT's Fathom software and model the piping and pump curve. www.aft.com for a demo download.

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! Already a Member? Login


White Paper - Addressing Tooling and Casting Requirements at the Design Stage
Several of the tooling and casting requirements of a part can be addressed at the design stage. If these requirements are not addressed at the design stage, lot of time is spent in design iteration when the design reaches the die caster. These design issues lead to increase in time and cost of production leading to delay in time to market and reduced profits for the organization. Download Now
White Paper - The Other Side of Design for Assembly
Assembly level constraints need to be satisfied before the design can move downstream. This white paper will go through the various assembly level issues, which need to be tackled by various organizations on a regular basis. Know more about DFMPro, a design for assembly software. Download Now

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