Relationship between TDH and NPSHA in pump
Relationship between TDH and NPSHA in pump
(OP)
Hi,
What is the effect of having a very high Total Differential Head. The reason for my question is:
NPSHA for the pump is 18 m
TDH is 18m
Is there any relationship with the two?
thanks for your responces.
What is the effect of having a very high Total Differential Head. The reason for my question is:
NPSHA for the pump is 18 m
TDH is 18m
Is there any relationship with the two?
thanks for your responces.





RE: Relationship between TDH and NPSHA in pump
There is dependancy between pump flowrate and NPSHR (due to higher friction losses when liquid accelerates at the eye of impeler at higher flowrates), and it is usually given as chart-type data NPSHR vs Q.
There are many free internet resources for centrifugal pump design and operation, some of them are:
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Regards
http://antwrp.gsfc.nasa.gov/apod/astropix.html
RE: Relationship between TDH and NPSHA in pump
R is requires - that is the minimum for the pump
A is avaiable - thats a calculated value and should be higher than R. There is no relationsship as such between TDH and NPSHA. NPSHA will be dependant on piping and flowrate.
Best regards
Morten
RE: Relationship between TDH and NPSHA in pump
" What is the effect of having a very high Total Differential Head. The reason for my question is:
NPSHA for the pump is 18 m
TDH is 18m "
In this case I don't see that you have a very high differential head irrespective of what NPSHa you have available. A bit more information or a clearer description of what you have would help with our advice.
RE: Relationship between TDH and NPSHA in pump
RE: Relationship between TDH and NPSHA in pump
RE: Relationship between TDH and NPSHA in pump
TDH = Against - Aid
this means that you are going to sum all the elements against your pump and substract all the elements that help your pump (height, pressure etc)
So if you are having a very very big TDH means you need a big pump roughly speaking. If TDH is negative it means that your pump probably is not needed (maybe you want to increase pressure and the pump is then justified). However this is all about convention of signs.
Now the relation between TDH and NPSHA is that NPSHA is your "Aid- vapor pressure"
RE: Relationship between TDH and NPSHA in pump
18m NPSHr for such a pump is a schoolboy design,most of our units are down to 0.8-0.9 metres, then we can look at Inducers on the Impellers if we need to go even lower than that.
Have a look at some curves from www.cdrpumps.co.uk to see some NPSH figures.
Ash Fenn
www.cdrpumps.co.uk
RE: Relationship between TDH and NPSHA in pump