What does it mean NPSH?
(Net Positive Suction Head)
Before the binning we have to illustrate couple things so we`ll be clear about everything:
Head= is the pressure expression
Hs= the head at the suction side
Hv= the head vapor(for the liquid)
Vs= velocity at the suction side
g= gravity acceleration (9.8 M/s^2, or 386.1 In/s^2)
Pv= vapor pressure ( for the liquid)
Y= weight in (N/m^3 or Ib/ft^3)
Now let`s simplify the theory for the NPSH,
What is it matter for?
How we can generate it ?
Can we characterize anything out of it?
lets start with the NPSH; it is the difference between the Head at suction side and the vapor head (pressure) of the liquid itself, that`
s why we have to avoid making the suction head less the vapor pressure `cause that going to :
decrease the efficiency
We can express the formula of the Head at suction side:
And about Hv= Pv/Yvapor
So the final formula of the NPSH(m,in)= Ps/Yliquid+Vs^2/2g-Pv/Yvapor
But put in mind that all conditions above based on the fixed temperature. for instant water boiling point at 20C(when absolute pressure =2.3KB/M^2) ,and 100C at (101.3KN/M^2).
Further than that,let`s speak about NPSHa or available NPSH, for pumping a liquid from the tank to another tank
hl= head loss between tank and implere end
where the (he) elevation head
Now if the pump above tank level the NPSH will be decreased(he)positive. be notified sometimes when the NPSH reach Zero, the fluid starts evaporate.
But if the pump below the tank the NPSH will increase.
To increase or decrease the NPHS it is clear what to do now as long as the head loss are fixed it is easy to optimize NPSH according to the physical or system requirements.
Now it is so clear why the pump of the water going to be different from the oil,fuel, air pumps,regardless the technical detail if we have the pump on a plane surface, dealing with two different levels situation, or bank of pumps.
From the maintenance point of view ; what if we need to isolate one off the service, or just making a lubrication
To be continued