Is psi the same as psia?
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civilized_naah
Well-known member
psia is still psi. The 'a' at the end represents Absolute (real) pressure. As opposed to psig, which is also psi, but a Gage pressure, which is the pressure (difference) recorded by a gage or device, which has to have a reference pressure. The most convenient reference pressure is atmospheric pressure. Therefore
sig = psia - reference pressure in psi
Sschell
Dude?
^close... but not quite.
PSI is a unit
in PSIA the unit is PSI, but zero is defined as absolute zero.
PSIG is gage pressure, PSI is still the unit, but zero is defined as ambient atmosphereic pressure (so the difference between PSIA and PSIG is typically 14.7 PSI i.e. 0 PSIG = 14.7 PSIA)
PSID is differential, again, PSI is the unit, but this refers to the difference between two measurement points. This is frequently used to measure pressure drop across an orfice (for example). PSIG can be seen as a subset of PSID, where your low side measurement point is ambient pressure.
edit: oh yeah, if something specifies only "PSI" with out the word atmosphere or difference/differential then it means PSIG. This is standard useage.
PSI is a unit
in PSIA the unit is PSI, but zero is defined as absolute zero.
PSIG is gage pressure, PSI is still the unit, but zero is defined as ambient atmosphereic pressure (so the difference between PSIA and PSIG is typically 14.7 PSI i.e. 0 PSIG = 14.7 PSIA)
PSID is differential, again, PSI is the unit, but this refers to the difference between two measurement points. This is frequently used to measure pressure drop across an orfice (for example). PSIG can be seen as a subset of PSID, where your low side measurement point is ambient pressure.
edit: oh yeah, if something specifies only "PSI" with out the word atmosphere or difference/differential then it means PSIG. This is standard useage.
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Water flows at 5 gpm in a 1 in schedule-40 rigid steel pipe. If the initial pressure in the pipe is 20 psig, the maximum pressure that results from a rapidly closing valve is most nearly
a 80 psi
b 120 psi
c 140 psi
d 160 psi
The deltaP i calculated is 122 psi, which gives 122+20=142 psig. But the absolute pressure should be 122+20+14.7=156.7 psia.
If psi means psig, then © is right. But if psi means psia, then (d) is right.
Can anybody check the result? I don't have it.
Thanks,
a 80 psi
b 120 psi
c 140 psi
d 160 psi
The deltaP i calculated is 122 psi, which gives 122+20=142 psig. But the absolute pressure should be 122+20+14.7=156.7 psia.
If psi means psig, then © is right. But if psi means psia, then (d) is right.
Can anybody check the result? I don't have it.
Thanks,
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Sschell
Dude?
my answer would be c (from the information you provided, I did not check your calculations)
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Sschell
Dude?
^water hammer.
IlPadrino
Well-known member
water hammer maximum surge pressure = aΔV/2.31g, where a=speed of sound (4856 fps in water), ΔV = 1.86 fps (instantaneous stop), 2.31 is the conversion factor from ft to psi, and g = 32.2 ft/sec-sec
answer=121psi+20psig=141psig and so I'd choose c.
answer=121psi+20psig=141psig and so I'd choose c.
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