Convert following reading of pressure to kPa, supposing that the barometer reads 760mm Hg.

(1) 90cm Hg gauge
(2) 40cm Hg vacuum
(3) 1.2m H2O gauge

Sol: Given that h = 760mm of Hg for P_atm

P_atm =   gh = 13.6 × 103  × 9.81 × 760/1000 = 101396.16

N/m² = 101396.16Pa = 101.39KPa                                                                          ...(i)

(a)  90cm Hg gauge

P_gauge = gh = 13.6 × 103  × 9.81 × 90/100 = 120.07KPa                                             ...(ii)

P_abs  = P_atm  + P_gauge = 101.39 + 120.07

P_abs  = 221.46KPa                        .......ANS

(b)  40cm Hg vacuum

P_vacc =  gh = 13.6 × 103  × 9.81 × 40/100 = 53.366KPa                                           ...(iii)

P_abs  = P_atm  - P_vacc

= 101.39 - 53.366

P_abs  = 48.02KPa                           .......ANS

(c)1.2m Water gauge

P_gauge  =   gh = 1000 × 9.81 × 1.2 = 11.772KPa                                                              ...(iv)

P_abs  = P_atm  + P_gauge

= 101.39 + 11.772

P_abs  = 113.162KPa          .......ANS