How is the head of a centrifugal pump specified! !
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Today at the meeting, one of the directors said that we damaged his pump; its designed head was 60m, but we had his staff force it to reach a head of 100m! I wonder if it’s possible? I think it’s impossible; I wonder what the experts have to say! Below is the definition of head that I found: Head refers to the height that a pump can lift water to, and it is usually denoted by H, with the unit being meters. The head of a centrifugal pump, measured with reference to the centerline of the impeller, consists of two parts. The vertical distance from the centerline of the water pump impeller to the water surface of the water source, that is, the height to which the water pump can draw water up, is called the suction lift, or simply the suction head ； The vertical height from the center line of the water pump impeller to the water surface of the outlet tank, that is, the height to which the water pump can lift water, is called the water lifting head, or simply the head. In other words, the pump head = suction head + discharge head. It should be noted that the head indicated on the nameplate refers to the head that the pump itself is capable of generating; it does not include the head loss caused by frictional resistance in the pipeline flow. This is something that cannot be ignored when selecting a water pump. Otherwise, water won’t be able to be pumped in.
This post was last edited by pair2cn on 2009-8-16 14:17. Are you referring to a positive displacement pump or a centrifugal pump? Head is the energy input by the pump into the liquid, measured in meters. In terms of measurement, it is the total pressure head of the liquid at the pump outlet flange minus the total pressure head of the liquid at the pump inlet flange. The head of a centrifugal pump is related to its flow rate; the higher the head, the lower the flow rate. If the head is increased from 60 m to 100 m, it increases by 66%. When selecting a centrifugal pump, the increase in head from the rated value to the shut-off point is generally not this large. If it is indeed a centrifugal pump, the pump may be operating at a flow rate below its minimum level or even with no flow at all; this can lead to increased vibration or cavitation, and damage can occur quite rapidly. If there is no flow or it is below the thermally stable flow rate, the pump will fail immediately. If it is a positive displacement pump, the reason is obvious.
I’m talking about centrifugal pumps! What are the causes of cavitation?
This post was last edited by pair2cn on 2009-8-16 at 16:44. The required NPSHr for a pump is at its minimum at the best efficiency point (BEP); as one moves away from this point, NPSHr gradually increases. If the head is increased by 66%, the flow rate will be much lower, and the corresponding NPSHr will increase significantly, which may lead to cavitation. To determine the specific cause of the pump failure, it is necessary to assess the condition of the impeller and bearings during maintenance.
In theory, a centrifugal pump can operate with its outlet closed, and this is also how it is usually operated during startup in practice. For centrifugal pumps, it is not necessary to keep the outlet valve closed when starting the pump; this is done only to reduce the starting current of the motor. However, if the outlet valve is not opened for an extended period after startup, or if it is opened only partially, the temperature of the liquid inside the pump will rise, which can easily lead to cavitation, severe vibrations, and damage to the impeller and seals. This also has a negative impact on the smooth operation of the motor. Typically, the minimum flow rate for a centrifugal pump should be at least 20-30%. As for \"the designed head is 60m, but it has been increased to 100m\”? I find it a bit strange; it’s highly unlikely! I don’t know what model of pump it is
This situation cannot occur; if the head is insufficient, it simply means that the pump is unable to transport the liquid upward – how could the pump itself get damaged? Even if you run the pump continuously for several days, it won’t get damaged, as insufficient head is not necessarily linked to pump damage
The pump’s head should be determined at the time of manufacture; how could it change arbitrarily? It’s unlikely that what the original poster is saying about increasing the head pressure will work.
This post was last edited by pair2cn on 2009-8-16 20:17. The operating point of the pump is determined by the resistance of the system. If we look at the performance curve of a centrifugal pump, we will find that different flow rates correspond to different head values. As for at which flow rate the pump operates, it depends on the resistance in the system, that is, the head. During operation, if the pump outlet control valve is continuously closed, the head that the pump must provide increases, while the flow rate decreases. When the pump’s flow rate drops below the minimum flow line, the vibration of the pump increases significantly; cavitation may also occur, accelerating the damage to the bearings and seals. No centrifugal pump can operate for a long time with the outlet valve closed. Low-head centrifugal pumps can operate for a short period of time with the outlet valve closed, and are only suitable for starting purposes. High-head centrifugal pumps, such as canned multi-stage pumps, must never be started or operated with the outlet valve closed under any circumstances. Whether a centrifugal pump can be started with the outlet valve fully open depends on whether the rated power of the motor, when selecting the pump, is greater than the shaft power corresponding to the end point of the pump’s performance curve. If the motor has insufficient power, it may burn out.
If the pump is fixed, then the head will also be fixed; I don’t quite understand what the original poster is saying
Generally, the head indicated on the nameplate of the pump refers to its maximum operating level; there is usually not much difference. It’s impossible to increase a head of 60M to 100M – under such a load the motor would burn out long ago~
The author’s claim that a head of 60m can be increased to 100m is probably not correct; generally, the maximum head that a pump can achieve is only 1.1 times its designed head. Either there is pressure at the inlet of the pump itself, or the density of the medium is high.