7 replies to this topic

[ahyong]

Dear All,

I have questions regarding pump hydraulic calculation.

1. As I know, when we do the pump hydraulic calculation, we will get the pipeline elevation according to the ISO drawing from piping team. But I was told that sometimes we need to take the elevation of every stream separately. I don't really understand what does it mean by" taking the elevation of specific stream separately" I hope someone could give me some guidance regarding this problem.

 

2. If there is heat exchanger at the suction side of the pump, what should be taken into consideration and how will it affect the pump when doing pump hydraulic calculation?

 

3. What will happen to the pump application when the pump performance curve is flat? (I don't really understand what does this question mean)

 

Thank you upon any explanation provided~

[Raj Mehta]

1. I have personally never come across such a thing and in what reference is it talking about. ?

 

2. If there is a heat exchanger in the pump suction, you have to consider the pressure drop across it while doing pump hydraulics. Note the velocity should not be too high (do the line sizing accordingly) to enhance the frictional losses in the suction, which will have an impact on the NPSHa for your system. Also pay attention to the temperature of the stream that is going to the pump, it should be far from its boiling point, just to ensure that it does not form vapor bubbles, which will damage your pump internals. 

 

3. I guess it is the condition in which you have flat head curve - meaning, with a increase in friction head over the period of pump run life, a large flow would be required to compensate for the losses and achieve the desired head. (generally in case of parallel operating pumps)

[latexman]

1. It could mean - consider the maximum elevation of each line to be sure the pump selected can fill the line at start-up.  When going from the suction vessel/tank to the fluid destination, many lines go high into the pipe rack or up into the process structure and then back down to the final destination.  At start-up with an empty line, the selected pump must have enough head to fill the highest point.

[binzee]

My two cents,

 

In case pump suction has multiple streams, then individual height may be required to ascertain the maximum suction pressure for suction piping etc...

 

I leave that to Che Jedis' to comment 

[ahyong]

Dear All,

 

First of all, thank you very much for the comments!

 

I have some comments regarding Raj Mehta's reply number 3.  In case of increasing friction head over the period of pump run life, the pump will slowly lose its performance and finally the head (destination height) that it can pump will reduce gradually. So, how does a large flow can compensate with the losing head? According to bernouli, pressure drop is proportional to the square of flow. The bigger the flow, the bigger the pressure drop so how does it compensate for the head loss? Please correct me if I misunderstood the contents meaning.

Thank you~

[Raj Mehta]

Well ahyong,

I guessed my 3rd point, and was not sure about its validity also your explaination seems correct, making my last point absurd and invalid.

Also other members views would be appreciated on this point.

 

I am now equally curious as you, to find out the what it means by flat head curve and what are its consequences. 

 

Thank you. 

[ankur2061]

Raj,

 

A flat pump curve (Q Vs H) indicates that the head does not change significantly with increase or decrease in flow. Some company standards specify a minimum head rise as flow is reduced to shut-off (or zero flow). For example, in one company standard the following is mentioned:

 

The head / capacity characteristic curve shall continuously rise as flow is reduced to shut-off (or zero flow). The minimum recommended rise is 12% with reference to the rated point. For parallel operation the head rise shall be between minimum 15% to maximum 20%.

 

 

Some links related to normal, flat and drooping pump characteristics are provide below with explanation of their characteristics:

 

http://www.pumpfunda...tips.htm#tips23

 

http://www.pump-zone...efficiency-0612

 

Regards,

Ankur.

[pardhasaradhi]

May I know what Firewater calculations are suppose to be calculated by HSE Design engineer, and what are the subsequent desirables by a HSE design engineer?