Practical Method for Pump Installation Height Calculation: Including Pipeline Loss and Pump House Requirements
To avoid cavitation, the installation height of the centrifugal pump needs to be carefully calculated and verified. A schematic diagram of the pump inlet side assembly is shown below:
The permissible geometric installation height of a pump depends on various factors, as shown in the following formula:
In the formula:
[Hg] — Permissible geometric installation height of the pump, m; (The calculation result is for design purposes only; the actual installation height must be lower than the permissible installation height)
Pe — Water surface pressure, Pa; (Atmospheric pressure at the water surface, lower at higher altitudes)
Pv — Saturated vapor pressure, Pa; (related to water temperature, the higher the water temperature, the higher the saturated vapor pressure)
ρ—the density of the fluid, kg/m³;
g—acceleration due to gravity, 9.81m/s²;
(NPSH)r—Permissible net positive suction head (NPSH) for the water pump, in meters (m); (Related to pump performance, provided by the pump manufacturer)
hw — Head loss in the suction line, in meters. (Related to the suction line design and determined by the designer)
From the above formula, we can see that:
The higher the altitude, the higher the water temperature, the larger the Net Positive Suction Head Required (NPSHr), the greater the head loss in the inlet pipe, and the smaller the allowable geometric installation height.
The atmospheric conditions and corresponding water head at different altitudes are shown in the table below:
Altitude (m) | Atmospheric pressure (kPa) | Head (m) |
|---|---|---|
-600 | 110.85 | 11.3 |
0 | 101.32 | 10.3 |
200 | 99.08 | 10.1 |
500 | 95.16 | 9.7 |
1000 | 90.25 | 9.2 |
1500 | 84.36 | 8.6 |
2000 | 79.46 | 8.1 |
3000 | 70.63 | 7.2 |
4000 | 61.80 | 6.3 |
5000 | 53.95 | 5.5 |
The table below shows the water head corresponding to the saturated vapor pressure of water at different temperatures:
Water Temperature ( °C ) | Saturated Vapor Pressure (kPa) | Head (m) |
|---|---|---|
10 | 1.23 | 0.125 |
20 | 2.34 | 0.238 |
30 | 4.24 | 0.433 |
40 | 7.37 | 0.752 |
50 | 12.33 | 1.272 |
60 | 19.92 | 2.066 |
70 | 31.16 | 3.249 |
80 | 47.36 | 4.97 |
90 | 70.10 | 7.406 |
100 | 101.32 | 10.786 |
Example: A certain brand of VISO125X100-315-55/2 water pump has a net positive suction head (NPSHr) of 3.29m. It is intended to operate at an altitude of 500m, where the highest summer water temperature is 40℃. If the head loss in the suction pipe is 1m, the geometric installation height [Hg] of the pump in this location is calculated as follows:
Assume the water pressure at the water surface is the local atmospheric pressure, and the atmospheric pressure head at an altitude of 500m is 9.7m from the table;
At a water temperature of 40℃, the saturated vapor head of water is 0.752m;
The calculation yields:
[Hg] = 9.7 - 0.752 - 3.29 - 1 = 4.658m
