Pressure at tank bottom valve during filling with inert gas blanket

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rachit mehra
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Hi all, this will seem a very easy problem for you guys but its really a bit conufusing for me..
I work on an oil tanker and the problem is as follows.
What will be the pressure on the filling line of a tank which is on deck when oil is being filled into the tank. For sake op simplicity let's take the density as 1.0. The tank is 20 metres deep and the valves are at bottom.( The entry point is on the top, and the oil flows down to the bottom of the tank and enters the tank at the bottom) . The tank has an inert gas blanket wih a pressure of about 400 mm water gauge.
Now my questions are-
1) What will be the pressure on the bottom line at the valve when a pressure gauge shows a pressure of 1 Bar.
2) If the tank is filled up to a height of 15 metres what will be the pressure then .

Thanks
 
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I suppose there will be a gas with oil too. Is it? Let's choose two points in tank. One is in liquid(A) and other is not(B).

Total pressures,

PA = Pgas + P liq
PB = Pgas

P liq = h d g

Also, if gas can not get out, even filling the tank, gas pressure will grow. If this is an ideal gas then,

PV=nRT

and n, R, T is not changing when filling. Thus,

PV= const.

Say, the gas has P pressure in tank and volume is V then, half of tank filled with liquid. Now,

PV = Pf*V/2 (Pf: Final pressure)
Pf=2P

hope this helps. (If i could understand properly)