Issues regarding the flow rate of the circulating water pump
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As shown in the figure. In the circulating water system, the circulating water pump has a rated head of 52 m and a flow rate of 3000 m3/h. During operation of the system, the pressure at the pump outlet is 0.60 Mpa, while the pressure in the system’s piping network is 0.44 Mpa. No flow meter is installed on the main pipeline. Is the flow rate of this pump equal to its rated design value?
First, look at the pump’s operation curve. If the head and flow rate at the operating point match the rated values, then check the height difference between the liquid level and the pump inlet; if this difference is around 9 meters, it’s likely fine, but if it’s less than 8 meters, the rated flow rate will not be achieved
Your control valve has been set to a lower value. Generally, circulating water pumps are variable-frequency pumps. It is recommended that if you have automated control, increase the opening of the control valve and reduce the frequency set by the inverter; this can help save energy. You only need to check the operating frequency of the variable-frequency device, as well as the pipe diameter and pressure levels, to determine roughly whether the rated flow rate has been achieved.
In previous years, variable-frequency drives were not widely used in circulating water pumps.
The water level in the pool is around 4.5 meters
The head is 52 m, the inlet pressure is 4.5 m – this isn’t considered to be resistance. The normal outlet pressure is 56.5 m; currently it’s around 60 m, indicating high outlet pressure. According to the general pattern of the pump’s performance curve, the head decreases as the flow rate increases, so it seems that the rated flow rate has not yet been reached
A pump has a rated flow rate and an actual flow rate. The rated flow rate corresponds to the rated head. The pump outlet pressure equals the inlet pressure plus the head. If the pump outlet pressure is lower than this value, it indicates that the pump is operating outside its optimal conditions. In other words, higher pressure results in a lower flow rate, while lower pressure leads to a higher flow rate. Your outlet is 0.6 and the main pipe is 0.44, which indicates that you have closed the valve. Only by adjusting the valve to the appropriate value can the rated flow rate be achieved. Of course, the possibility of inflated pump parameters cannot be ruled out.
Pressure 0.6, system pressure 0.44； Pressure is generated due to resistance; therefore, the outlet valve affects the operation of the pump, otherwise the outlet pressure should be equal to the system pressure. If it’s difficult to determine whether the pump is meeting the design parameters, it’s best to check the operating current. For centrifugal pumps, current is generated as a result of work being done; otherwise, the current will be low
It can be detected using an ultrasonic flow meter; the nameplates of many pumps do not match the actual conditions on site, and the main reasons for this are issues related to design selection and on-site installation procedures