×
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

Pump Affinity Laws

Pump Affinity Laws

Pump Affinity Laws

(OP)
Pumps basics:
Centrifugal Fire- Pump:

Impeller dia = constant, Power = Constant
Q1 = 1000-gpm, H1 = 335-ft
Affinity Law: (H2/H1) = (Q2/Q1)^2
If Q2 = 100-gpm, H2 = 3.35-ft
Is this correct? The head should go up for lower flows for constant power and constant impeller diameter.
Why am I confused? Please help me understand

RE: Pump Affinity Laws

You don't need to use an affinity law to find pressure at a specific flow. Use the manufacturers pump curve. Flow will be on the x axis, pressure will be on the y axis.

RE: Pump Affinity Laws

The reason that it does not work is because Q1 and Q2 are porportional to n1 and n2; H1 and H2 are proportional to n1^2 and n2^2. The only time Q1/Q2= (n1/n2)^2 works is when you have one curve (Q1,H1) is based on n1 and the second curve(Q2,H2) is based on n2.

RE: Pump Affinity Laws

To finish off what I have stated, to apply the affinity equations that you presented, you'll have two curves; one curve will be based on RPM N1 and the second curve will be based on RPM n2 which would incorporate your 100 rpm @ 3.35 ft of head. Follow skdesigner's original reply.

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