【2026 Rotating Equipment】Calculation of the installation height (suction lift) for pipeline centrifugal pumps
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I. Key installation techniques for centrifugal pumps The key to the installation technique of pipeline centrifugal pumps lies in determining the installation height of the pump (i.e., the suction head). This height refers to the vertical distance from the water surface to the centerline of the pump impeller. It should not be confused with the allowable suction vacuum level. The allowable suction vacuum level indicated in the pump’s manual or nameplate refers to the vacuum value at the pump’s inlet section, and it is determined through tests conducted under 1 standard atmosphere and a water temperature of 20 degrees Celsius. It does not take into account the water flow conditions after the installation of the water absorption pipes. The installation height of the water pump should be the value remaining after deducting the head loss in the water intake pipeline from the allowable suction vacuum height; this height is necessary to overcome the actual topographic constraints related to the water intake height. The installation height of the water pump must not exceed the calculated value; otherwise, the pump will not be able to draw water.
Furthermore, the resistance loss head of the water intake pipeline affects the magnitude of the calculated value; therefore, it is advisable to use the shortest possible pipeline layout and minimize the use of fittings such as elbows. It is also possible to consider using pipes with a larger diameter in order to reduce the flow velocity inside the pipes.
When the elevation and water temperature at the installation site of the pipeline centrifugal pump differ from the test conditions, such as when the local altitude is above 300 meters or the temperature of the water to be pumped exceeds 20 degrees Celsius, the calculated values need to be adjusted. That is, the atmospheric pressure at different altitudes and the saturated vapor pressure at water temperatures above 20 degrees Celsius. However, when the water temperature is below 20 degrees Celsius, the saturated vapor pressure can be disregarded.
From the perspective of pipeline installation techniques, water intake pipes require strict sealing to prevent air or water leakage; otherwise, it will disrupt the vacuum level at the water pump’s inlet, resulting in a reduced water output from the pump (WeChat official account: Pump Butler). In severe cases, the pump may not be able to draw in any water at all. Therefore, it is necessary to carefully carry out the pipeline joint work to ensure the construction quality of the pipeline connections.
II. Calculation of the installation height Hg of centrifugal pumps. The allowable suction vacuum height Hs refers to the maximum degree of vacuum that can be achieved at the pump inlet pressure p1. The actual allowable suction vacuum height Hs value is not the one calculated using the formula, but rather a value determined through experiments by the pump manufacturer; this value is included in the pump manual for users’ reference. It should be noted that the Hs value given for the pump samples is based on clean water as the working medium, under operating conditions of 20°C and a pressure of 1.013×105 Pa; conversions are required when the operating conditions or the working medium differ.
(1) For transporting clean water, but when the operating conditions differ from those in the experiment, the conversion can be done using the following formula: Hs1＝Hs＋(Ha－10.33)－(Hυ－0.24)
(2) Transporting other liquids: When both the liquid to be transported and the operating conditions differ from those in the experiment, a two-step conversion is required. The first step is to use the formula above to determine Hs1 from the pump sample ； In the second step, Hs1 is converted to the NPSH Δh using the following formula.
For oil pumps, the installation height is calculated using the net positive suction head Δh, which represents the vacuum level at which the pump can draw in liquid; it also indicates the maximum allowable installation height of the pump, with the unit being meters. The net positive suction head Δh is obtained from the oil pump data sheet, and its value is also determined using water at 20°C. If other liquids are to be transported, calibration is also required; consult relevant books for details.
Suction lift = Standard atmospheric pressure (10.33 meters) – NPSH – Safety margin (0.5 meters). The standard atmospheric pressure can create a vacuum in the pipeline up to 10.33 meters.
For example: If a pump requires a net positive suction head of 4.0 meters, what is the suction lift Δh? Δh=10.33-4.0-0.5=5.83 meters
From a safety perspective, the actual installation height of the pump should be less than the calculated value. When the calculated Hg is negative, it indicates that the pump’s suction inlet should be located below the liquid level in the tank. For example, it is found from the specifications of a certain centrifugal pump that the allowable suction vacuum height Hs is 5.7 m. It is known that the total resistance of the suction pipeline is 1.5 mH2O, the local atmospheric pressure is 9.81×10^4 Pa, and the dynamic head of the liquid in the suction pipeline can be ignored. Calculate: (1) The installation height of the pump for transporting water at 20°C. (2) Change to the installation height of the pump when transporting 80°C water.