5 replies to this topic

[jatinder]

Dear All,

 

I am busy learning about Centrifugal Pumps. I am able to perform most of the calculations such as calculations regarding Suction head, discharge head, Total head, NPSHa etc. However, the other very important thing is to get familiar with all these terms. I am little bit confused with the term "Total Head". 

 

We know that Total head of the Centrifugal pump is = Total Discharge head - Total Suction Head 

 

I am familiar with the term "Head" according to its definition but gets confused when I see it in Numerical Form. 

 

Attached please find the rough drawing for better understanding of my question. I would like to know that what does it really mean (in practical term) when the "Total Head" of the pump is a positive number or negative number. 

 

In CASE 1 of attached drawing:

 

I calculated:

 

Total Suction Head = 20 mlc (Please ignore P1 and friction losses)

Discharge Head = 145.35 mlc

 

Therefore Total Head = 145.35 - 20 = 125.35 mlc (This is a positive Number)

 

 

In CASE 2

 

Everything is same except for that I increased the Static Suction head to 200 meter

 

Results

 

Total Suction Head = 200 mlc

Discharge Head = 145.35 mlc

 

Therefore Total Head = 145.35 - 200 = -54.65 mlc (This is a negative Number)

 

So What does these positive Head and negative Head signifies in terms of practical situations. Theoretical is fine, anybody can learn theory calculations learning the formulas but I need to know it in a Practical way.

 

Thank you so much in advance!

Attached Files

•  Screenshot_1.jpg   38.66KB   1 downloads

Edited by Art Montemayor, 05 August 2015 - 12:15 PM.

[shan]

Total Head = Pressure Head + Elevation Head + Speed Head

Edited by shan, 05 August 2015 - 12:29 PM.

[thorium90]

You have forgotten to add the head that the pump adds to the water.

If you just do the following, Total Head = 145.35 - 200 = -54.65, it means there is no pump, which means the logical conclusion that the water in the higher tank flows into the lower tank as if there is no pump...

[jatinder]

You have forgotten to add the head that the pump adds to the water.

If you just do the following, Total Head = 145.35 - 200 = -54.65, it means there is no pump, which means the logical conclusion that the water in the higher tank flows into the lower tank as if there is no pump...

 

Thank you Thorium90,

 

It is clear to me now that negative value means that no pump is required.  But what do you mean by stating that I forgot to add the head that the pump adds to the water? 

[thorium90]

Don't worry about it. Not adding it would mean the same thing as not having any pump.

[breizh]

http://www.pumpworld...on-tutorial.htm

 

http://www.pumpfunda...e.htm#download6

 

Jatinder , 

 

You should find good information in these websites to support your studies , on top of all advises you can get from this forum .

 

Hope this helps

 

Breizh 

Edited by breizh, 06 August 2015 - 07:51 PM.