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This is not a real system but rather something I made up to understand how the placement of pressure gauge in a tank takes its readings.

Here’s a diagram of it- enter image description here

The pressure gauge placed in the middle of the tank. Let’s say I’m working in gage pressure.

Which point in the tank does this pressure gauge measures until ?

Does it measure till the middle point only ?

For example - pressure at the level where pressure gauge is placed - P (vapor) + P (liquid at h=1m) = $120 + \rho g h$ = ____ kpa

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  • $\begingroup$ and what about the pressure due to the mercury column? $\endgroup$
    – Solar Mike
    Commented Aug 18, 2018 at 9:17
  • $\begingroup$ @SolarMike that is just to compare the pressure in the tank to the atmosphere isn’t it ? $\endgroup$
    – user185692
    Commented Aug 18, 2018 at 11:13
  • $\begingroup$ Is it? Have you evaluated that? $\endgroup$
    – Solar Mike
    Commented Aug 18, 2018 at 11:16

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Yes, If you remove mercury manometer, then the pressure measured will be $P = 120000 + \rho *9.81 * (1m)$.

If you want to measure the pressure at the bottom of the vessel with the mercury manometer, make sure the pipe connecting the limb and vessel is filled with air. (just to avoid hydrostatic pressure by the fluid inside the connecting pipe). This would be difficult.

The best method I could think is, go for single limb manometer and keep the bottom of the limb and the bottom of the vessel are at the same level (head).

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From what I have learned at university, pressure in a vessel is equal at all points of the interior surface. This means it does not matter where the measuring gauge is placed.

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    $\begingroup$ If the vessel of non-negligible height is filled with liquid, this is definitely not true as the pressure at the bottom will be considerably larger. And 2m of water exert a good 20 kPa more on the bottom than on top. $\endgroup$
    – SF.
    Commented Aug 24, 2018 at 8:46

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