Slide rule calculation for speed changes in centrifugal pumps

It has been a while since I have operated any moving equipment like a "slip-stick", but the fan or pump affinity laws come into play.

FLOW varies directly with RPM, flow1/flow2 = rpm1/rpm2

PRESSURE varies with the Square of RPM, p1/p2 =(rpm1/rpm2)^^2

POWER varies with Cube of RPM, HP1/HP2 = (rpm1/rpm2)^^3

Thanks Ried, but we know the affinity laws, we just can't remember how to use a slide rule.

You guys are all way too young for me. I remember how to use the slip stick to find squares and cubes (Squares can be read directly off of the A scale and square roots can be read from the C scale. For example to find the square of 2, just set your hairline on the 2 on the C scale and read the square (4) on the A scale. The only trick comes from figuring which side of the A scale to use when finding square roots. I'll give you a clue, it depends on the number of digits... Cubes use the K scale... I just can't remember how to use my calculator... I am Mathcad dependant now...

I want to suplement for the note of (Sl. No.3 ANONYMOUS POSTER) for slide rule. As Mr.Shyprum (No.4 in this post) expressed SLIDE RULE basic concept is based on LOGARITHM and ANTILOGARITHM.

For MULTIPLICATION set the cursor at the multiplying number at the slde rule and allign the slide to the cursor hair-line. Then move the cursor hair-line to the number to multiplied. Now you read the Number at he base scale. That is the product.

For multiplication the left side 1 should be alligned to the cursor hair-line and for division the right side 1 has to be alligned to the cursor hair-line.

Now fixing of digits is the need. If the cursor moves right side, the number of digits in the multiplying nomber + number of digits in the number to multiplied -1 is the answer. If the cursor moves to left the number of digits in the multiplying number + number of digits in the multiplying number -0 is the answer.

For example 2x3=6. In this case cursor will move to right hand, so (1+1) -1= 1, the answer is single digit.

For example 5x4=20. In this case the cursor will go to left hand, so (1+1)-0= 2, the answer is double digit.

With the Slide Rule how to use guide will be there and refer it.

DHAYANANDHAN.S

Slide rules are mechanical devices for producing and manipulating logarihms, if you wan't to get a feel of how they work use a normal calculator to evaluate logarithms and then add, subtract and multipy them etc, you will soon be glad that you live in a post sliderule age.