Converting head to presssure (psia or psig?)

[JBrou]

First off this may be a stupid question but I cant seem to figure this out from any online sources. I'm pretty new (currently interning) but I feel like I have a pretty good grasp of NPSHa/NPSHr and how to calculate them until my mentor ran across this diaphragm pump that he says was incorrectly speced out and has an NSPHa problem.

The pump shows:
NPSHa = 10.3 ft
NPSHr = 9 psia

So my question is: When you convert from head to pressure how do you know if it is absolute or gauge pressure?

Obviously, if you look at a pump curve it would just be psi since it's a differential pressure, but what if you just want to know the pressure at the bottom of a tank with a water level say 10 ft high? I would initially think it would be 10'/2.31 = 4.33 psig but now I'm thinking twice about that assumption.

Any advice would be greatly appreciated!

 

[GHartmann]

LittleInch:

I believe we are in agreement. I added the term "absolute" in parenthesis behind feet to make sure the conversion had been made from absolute pressures.

We are definitely in agreement about using absolute pressures throughout.

For me I always converted these to head and did the pump hydraulics in "head" units. That has kept me straight for more than 30 years.