Question

Convert the following readings of pressure to kPa, assuming that the barometer reads 760 mmHg:

(a) 90 cm Hg gauge

(b) 40 cm Hg vacuum

(c) 1.2 m H₂O gauge

(d) 3.1 bar

Answer 1

760 mm Hg = 0.760 × 13600 × 9.81 Pa

= 10139.16 Pa

= 101.4 kPa

(a) 90 cm Hg gauge 

= 0.90 × 13600 × 9.81 × 10^-3 + 101.4 kPa

= 221.4744 kPa

(b) 40 cm Hg vacuum

= (76 – 40) cm (absolute)

= 0.36 × 43.600 × 9.81 kPa

= 48.03 kPa

(c) 1.2 m H₂O gauge

= 1.2 × 1000 × 9.81 × 10^-3 + 101.4 kPa

= 113.172 kPa

(d) 3.1 bar

= 3.1 × 100 kPa

= 310 kPa