EXAMPLE 1
Problem: If a pressure instrument has a reading of 30 psig, find the absolute pressure if the local barometric reading is 14.6 psi.
Solution: Since Pg > Patm, use Equation 1-A to find the absolute pressure:
Pa = Pg + Patm
Pa = 30 psi + 14.6 psi
Pa = 44.6 psia
EXAMPLE 2
Problem: Find the absolute pressure if a vacuum gauge reads 11.5 psig and
the atmospheric pressure is 14.6 psia.
Solution: When dealing with pressure below atmospheric pressure, you must
use Equation 5-B:
Pa = Pg – Patm
Pa = 11.5 psi – 14.6 psi
Pa = – 3.1 psia