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Bar (Gauge) Or Bar (Absolute)


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#1 farid.k

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Posted 10 July 2017 - 03:59 AM

i become confuse when calculating the pump NPSHa. one of the factor that we need to consider is the source pressure i.e. let say the LPG bullet tank operating pressure 10 barg, in order to have figure in head (m), do i need to convert to bar absolute first? which is becomes 11.01325 bara than convert to head? or just straight convert 10 barg to meter head?

 

let say just convert it using gauge pressure, does it means that ATM tank will be having 0 meter head in term of source of pressure?



#2 breizh

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Posted 10 July 2017 - 05:45 AM

Hi Farid ,

Use these resource to clear your doubt.

Page 1 of the excel sheet is an example .

Hope this helps

 

Breizh


Edited by breizh, 10 July 2017 - 06:15 AM.


#3 ankur2061

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Posted 10 July 2017 - 06:25 AM

Hi,

 

Use anything as long as you are consistent. If you use barg for source vessel pressure then use vapor pressure also in barg for NPSHa calculations. Friction losses or any pressure drop (suction filter pressure drop) is not categorized as gauge or atmospheric notation. It is just a differential and in Imperial units is often defined as psid where the d stands for differential.

 

Regards,

Ankur



#4 fallah

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Posted 10 July 2017 - 06:48 AM


 

Hi Farid,

 

Because the vapor pressure is mostly reported in absolute value, in order to prevent any mistake it's better the source pressure to be reported and utilized in absolute value, too.
 



#5 farid.k

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Posted 10 July 2017 - 07:00 AM

How about static head sir? Rho*g*h then the pressure from them just simply consider gauge (incase the other parameter we consider gauge or vise versa)



#6 ankur2061

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Posted 10 July 2017 - 11:24 AM   Best Answer

Farid,

Again static head is a difference in pressure from point 1 to point 2, hence in one set of units it will be consistent I.e.if you are using gauge then use gauge and if absolute then absolute. It's numerical value does not change irrespective of gauge or absolute units.



Regards,
Ankur




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