Pump head
Thread Content
What determines the head of the pump to be chosen?
The pump head is selected based on the maximum height difference for material transfer, the density of the material, the viscosity of the material, and the pressure drop in the pipeline.
Select the pump head based on the pipeline characteristics
H head is greater than or equal to H pipe resistance + H level difference – H pressure before the pump + H pressure in the receiving tank
The following documents are provided for your reference: the suction lift of pipeline centrifugal pumps, that is, the installation height and its calculation method. I. Key installation techniques for centrifugal pumps The key to the installation techniques of pipeline centrifugal pumps lies in determining the installation height of the pump (i.e., the suction lift). 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 topographical 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. It should be noted that when the elevation and water temperature at the installation site of the pipeline centrifugal pump differ from those in 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 (0.24 meters at 20 degrees Celsius) can be considered negligible. From the perspective of pipeline installation techniques, water intake pipes require strict sealing to prevent air or water leaks; otherwise, it will disrupt the vacuum level at the water pump’s inlet, resulting in a reduced water output from the pump, and in severe cases, the pump may even fail to draw in water. Therefore, it is necessary to carry out pipeline joint work carefully to ensure the construction quality of the pipeline connections. II. Calculation of the installation height Hg for 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 is not a value calculated from the formula, but rather a value determined through experiments by the pump manufacturer; this value is included with the pump sample for the user’s reference. It should be noted that the Hs value given in the pump specifications applies when clean water is used 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, conversion can be done using the following formula: Hs1 = Hs + (Ha – 10.33) – (Hυ – 0.24).
(2) For transporting other liquids, when both the properties of the liquid being transported and the operating conditions differ from those in the experiment, two steps of conversion are required: the first step involves using the formula above to determine Hs1 based on the values provided for the pump ； In the second step, Hs1 is converted to Hs using the following formula. The net positive suction head Δh: For oil pumps, the installation height is calculated using the net positive suction head Δh, which represents the vacuum level that the pump can tolerate when drawing 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; refer to 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? Solution: Δh = 10.33 – 4.0 – 0.5 = 5.83 meters. For safety reasons, the actual installation height of the pump should be less than the calculated value. When the calculated Hg value is negative, it indicates that the pump’s suction inlet should be located below the liquid level in the tank. Example: For a certain centrifugal pump, the allowable suction vacuum height Hs as determined from the specifications is 5.7 m. It is known that the total resistance of the suction pipeline is 1.5 mH2O, the local atmospheric pressure is 9.81×104 Pa, and the dynamic head of the liquid in the suction pipeline can be neglected. Try to calculate: (1) Pump installation for transporting water at 20°C ； (2) Change to the pump installation height when transporting 80°C water. Solution: (1) Installation height of the pump when transporting water at 20°C. Given: Hs = 5.7 m, Hf0-1 = 1.5 m, u12/2g ≈ 0. The local atmospheric pressure is 9.81×10^4 Pa, which is roughly consistent with the conditions under which the pump was tested during manufacturing; therefore, the installation height of the pump is Hg = 5.7 – 0 – 1.5 = 4.2 m. (2) Installation height of the pump when transporting water at 80°C When transporting water at 80°C, it is not possible to use the Hs value given in the pump specifications to calculate the installation height; instead, Hs must be adjusted using the following formula: Hs1 = Hs + (Ha – 10.33) – (Hυ – 0.24). Given that Ha = 9.81×10^4 Pa ≈ 10 mH2O, the saturated vapor pressure of water at 80°C is 47.4 kPa, as stated in the appendix. Hv = 47.4×10³ Pa = 4.83 mH2O. Hs1 = 5.7 + 10^–10.33 – 4.83 + 0.24 = 0.78 m. The installation height is determined by substituting the value of Hs1 into the formula: Hg = Hs1 – Hf0 – 1 = 0.78 – 1.5 = –0.72 m. A negative value for Hg indicates that the pump should be installed below the water level in the tank, at least 0.72 m below it.
(2) For transporting other liquids, when both the properties of the liquid being transported and the operating conditions differ from those in the experiment, two steps of conversion are required: the first step involves using the formula above to determine Hs1 based on the values provided for the pump ； In the second step, Hs1 is converted to Hs using the following formula. The net positive suction head Δh: For oil pumps, the installation height is calculated using the net positive suction head Δh, which represents the vacuum level that the pump can tolerate when drawing 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; refer to 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? Solution: Δh = 10.33 – 4.0 – 0.5 = 5.83 meters. For safety reasons, the actual installation height of the pump should be less than the calculated value. When the calculated Hg value is negative, it indicates that the pump’s suction inlet should be located below the liquid level in the tank. Example: For a certain centrifugal pump, the allowable suction vacuum height Hs as determined from the specifications is 5.7 m. It is known that the total resistance of the suction pipeline is 1.5 mH2O, the local atmospheric pressure is 9.81×104 Pa, and the dynamic head of the liquid in the suction pipeline can be neglected. Try to calculate: (1) Pump installation for transporting water at 20°C ； (2) Change to the pump installation height when transporting 80°C water. Solution: (1) Installation height of the pump when transporting water at 20°C. Given: Hs = 5.7 m, Hf0-1 = 1.5 m, u12/2g ≈ 0. The local atmospheric pressure is 9.81×10^4 Pa, which is roughly consistent with the conditions under which the pump was tested during manufacturing; therefore, the installation height of the pump is Hg = 5.7 – 0 – 1.5 = 4.2 m. (2) Installation height of the pump when transporting water at 80°C When transporting water at 80°C, it is not possible to use the Hs value given in the pump specifications to calculate the installation height; instead, Hs must be adjusted using the following formula: Hs1 = Hs + (Ha – 10.33) – (Hυ – 0.24). Given that Ha = 9.81×10^4 Pa ≈ 10 mH2O, the saturated vapor pressure of water at 80°C is 47.4 kPa, as stated in the appendix. Hv = 47.4×10³ Pa = 4.83 mH2O. Hs1 = 5.7 + 10^–10.33 – 4.83 + 0.24 = 0.78 m. The installation height is determined by substituting the value of Hs1 into the formula: Hg = Hs1 – Hf0 – 1 = 0.78 – 1.5 = –0.72 m. A negative value for Hg indicates that the pump should be installed below the water level in the tank, at least 0.72 m below it.
The pump head is selected based on factors such as the distance and height of material transfer, pipeline resistance, and material viscosity.
The head is primarily calculated based on the physical properties of the conveyed medium and the characteristics of the pipeline.
It would be best to do the calculations actually; things that are too general are not easy to understand. I hope some expert can provide an example calculation for us to see