ABSTRACT
Older VIEs are mounted on three legs, two of which form a hinge, and the third is a spring balance (Figure 8.18a). The weight of the liquid O2 remaining gives a measure of its level and need for refilling. Modern installations have internal pressure transducers at the
Formula of molecular oxygen O2
Molecular weight 32 daltons
Density of gas at 1 bar, 15°C 1.34 kg/m3
Density of liquid oxygen at 1 bar, –183°C 1140 kg/m3
Boiling point (BP) at 1 bar –183.1°C
Critical temperature –118.4°C
Critical pressure 50.8 bar
Critical density 430 kg/m3
Figure 8.16. A liquid O2 installation suitable for supplying a hospital. Note the presence of the emergency cylinder bank at the rear (Courtesy of the Birmingham Women's Hospital NHS Trust.)
Figure 8.17. Diagrammatic representation of the mechanism of action of a liquid O2 supply system (see text for details). (Adapted from Howell RSC. Anaesthesia 1980; 35:676.)
top and bottom of the tank. The difference between the two gives the depth of the liquid O2 and this, together with the cross-sectional area, allows the volume of liquid O2 to be calculated or read off a calibration chart (Figure 8.18b). All VIE installations have next to them a reserve cylinder bank and enough cylinders on site to supply a typical 24-hour need (Figure 8.16).
