I have a big problem with pressure's units
I know that P (psig) = (P + 14.7) psia
But my problem with psi
as an example, 20 psi = ?? in psia or psig ??
PSIA is measured in units of PSI and the reference for zero PSIA is a perfect vacuum.
A pressure gauge reads the pressure difference between its location and the ambient pressure. PSIG is gauge pressure, also measured in units of PSI. The zero for PSIG is ambient or atmospheric pressure at sea level, (on Earth, approx 14.7 PSI), that is why PSIG - 14.7 = PSIA