I have lack of experience in calculating NPSHa in the field. I looked at some books that show how to calculate the NPSHa but I still need to know how i can apply in the field.

well here is some of the parameters reading:
flow rate 270M^3/hr
tank temp 108F
Tank Pressure -79mbar

I am sure there will be more data to be put here, just tell me what data you need to know.

NPSH AVAILABLE= H (ATMOSPERIC)+- SUCTION HEAD -FRICTIONAL LOSSES IN SUCTION LINE- H (VAP PR. AT PUMPING TEMPERATURE). WHERE
H(ATMOSPHERIC)=ATMOSPHERIC PRESSURE=10.33 MTR OF WATER COLUMN AT STANDARD PRESSURE AND TEMP (CONVERT TO RELEVANT HEIGHT FOR THE RELEVANT FLUID).
SUCTION HEAD =TO BE ADDED IF IT IS POSITIVE HEAD. IT IS TO BE DEDUCTED IF IT IS SUCTION LIFT. IT IS 79 mBar POSITIVE HEAD IN YOUR CASE. CONVERT IT TO PRESSURE HEAD.
FRICTION LOSSES= LOSSES IN PIPELINES , BENDS, ELBOWS , VALVES ETC. IN LINE FROM SUCTION POINT TO PUMP SUCTION NOZZLE TO BE CALCULATED.
H(VAPOR PRESSURE)=VAPOR PRESSURE AT THE PUMPING TEMP (108 F IN YOUR CASE)AND PRESSURE OF THE PUMPED LIQUID FROM STEAM TABLE.
HOPE THIS CLEARS.
REGARDS.
IRSHAD AKHTAR

Here is a pretty good site...

http://www.mcnallyinstitute.com/11-html/11-12.html

To calculate the losses that Irshad speaks of, refer to the Cameron Hydraulic Data book.

Basically, NPSHA is the amount of absolute pressure available on the suction side of the pump above that of the vapor pressure of the liquid in question.

data example

HTH's
BT