Specific Volume:

Before examining an example which shows the effects of density, the unit "specific volume" must be defined.  It is defined as volume per unit mass as display in Equation 3-1.

Specific Volume = Volume/Mass                                                (3-1)

Specific volume is a reciprocal of density as display in Equation 3-2.

Specific Volume = 1 /density                                                       (3-2)

It is the standard unit used while working with vapors and steam that have low values of density.

For the applications which includes water and steam, specific volume could be found using "Saturated Steam  Tables,"  that  list  the  specific  volumes  for  water  and  saturated  steam  at  various pressures and temperatures.

The density of steam (or vapor) above the liquid level will have an effect on the weight of the steam or vapor bubble and the hydrostatic head pressure.  As the density of the steam or vapor rise and the weight increases and causes an increase within hydrostatic head even by the actual level of the tank has not changed. The larger the steam bubble the greater the modification within hydrostatic head pressure.

Figure describes a vessel in that the water is at saturated boiling conditions.

Figure: Effects of Fluid Density

A condensing pot at the top of the reference leg is incorporated to condense the steam and manage the reference leg filled. As previously begin, the effect of the steam vapor pressure is cancelled at the ?P transmitter due to the fact in which this pressure is evenly applied to the low and high pressure both sides of the transmitter.  A differential pressure to the transmitter is because of only to hydrostatic head pressure, as begins in Equation 3-3.

Hydrostatic Head Pressure = Density x Height                         (3-3)