3. • When altitude
increases, pressure
decreases, and water
may boil at
temperature below
100°C.
• On every 27mmHg of
atmospheric pressure
increase, the boiling
point of water will
decrease 1°C.

5. Water vaporizing is
related to the
temperature and
also pressure.
T (°C) Ps (ata) Ps (kPa)
0 0.0062 0.6113
5 0.0089 0.8726
10 0.0125 1.2281
15 0.0174 1.7056
20 0.0238 2.3388
25 0.0323 3.1690
30 0.0432 4.2455
40 0.0752 7.3814
80 0.4829 47.3730
100 1.0332 101.3200
120 2.0245
160 6.302
Note:
1 ata = 10,0 m H2O
1 kPa = 101.97 mm H2O

6. The low pressure at the suction side of a pump
can encounter the fluid to start boiling with
• reduced efficiency
• cavitation
• damage
of the pump as a result. Boiling starts when the
pressure in the liquid is reduced to the vapor
pressure of the fluid at the actual temperature.

10. • NPSHr : Required net positive suction head to avoid
pump performance drop caused by cavitation.
• NPSHa : Available net positive suction head at
reference level of impeller inlet calculated by that total
suction head minus absolute vapor pressure of the
liquid.
• When NPSHR becomes larger than NPSHA, cavitation
occurs. The cavitation affects badly to pump and
pipings as shown before.
By this, the engineer should know how much
margin before the liquid becomes vapor.

12. Suction Lift
- 5m
Losses 1m
Reference
Line
Atm.
Press.
1 atm =
10.3 m H2O
NPSHa
= 10.3 – 0.3 – 1 – 5
= 4 m
Vapor Pressure 0.3m @ 25°C

13. Suction Lift
- 1m
Losses 1m
Reference
Line
Atm.
Press.
1 atm =
10.3 m H2O
NPSHa
= 10.3 – 4.8 – 1 – 1
= 3.5 m
Vapor Pressure 4.8m @ 80°C

14. Reference
Line
Height of water
Surface
3 m
Pressure Tank
2 bar = 20.4m H2O
Losses
2 m
NPSHa
= 20.4 + 3 – 4.8 – 2
= 16.6m
Vapor Pressure @ 80°C
4.8m

15. Height of water
Surface 8m
Losses
3m
NPSHa
= 8 +21.47 – 21.47 – 3
= 5 m
Pressure acts
On liquid surface
21.47m
Vapor Pressure
21.47m

16. • NPSHa = hsv: Available Suction Head (m)
• Ps: Pressure acting on suction water level (kgf/m2abs)
*absolute press. = gauge pressure + atm press
• Pv: Absolute saturated vapor pressure of fluid under
operating temperature (kgf/cm2abs)
• ɣ: Weight of fluid per unit volume under operating
temperature (kgf/m2)
• hs: Height from suction water level up to reference
level of impeller (m)
• ᶉVs2/2g: Total head loss in suction line (m)
NPSHa = hsv = Ps Pv
ɣ ɣ– ± hs – ᶉV2
2g