Answer / carl_ellis

A closed pressure vessel requires a differential pressure
measurement in order to compensate for the pressure or
vacuum in the vapor space above the liquid.

The density is said to be 1, so we'll assume that what was
really meant is that the specific gravity is 1.00, the same
as the specific gravity of water. The measurement can be
made in engineering units of mm of water column (wc) with no
compensation for a specific gravity other than water.

A DP transmitter measurement:
(high side pressure) minus (low side pressure)

The low side pressure reading is (vacuum pressure).
The high side pressure reading is (column of water pressure
+ vacuum pressure)

(water column pressure + vacuum pressure) minus vacuum
pressure = water column pressure.

With a vertical elevation difference between the flanges of
440mm, the water column pressure will be
0 - 440mm wc.
LRV = 0.0 mm wc
URV = 440 mm wc

Carl Ellis
Measure First

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