Pressure hold, minimum backflow? ? Seeking advice
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To prevent freezing in winter, one pump must remain operational at all times. The outlet size cannot be too large, as that would lead to waste; moreover, the process requirements do not call for such a large flow rate. However, the problem lately has been severe leakage from the machine seals. Of the two backup pumps, their seals have completely failed. My guess is that this is the cause of the issue; I’m not sure if it’s correct, so I hope everyone can help analyze it. The outlet is too small, causing pressure buildup that in turn damages the mechanical seal. Regarding this, I have considered the minimum backflow; are the installation locations the pipe outlet and the pipe inlet? How is the minimum flow rate calculated? What size of pipe is appropriate? Should the flow rate required be used as a reference, right?
Why not consider variable frequency drives for the motors? If it is a multi-stage pump, can the number of stages be reduced?
The minimum flow rate for the continuous operation of the pump is determined through measurement. According to API standards, if the vibration level in the preferred operating area is 3 mm/s, then the minimum flow rate corresponds to the point at which the vibration exceeds 3.9 mm/s. The pump also has a thermally controlled minimum flow rate, which needs to be calculated based on the specific heat capacity of the medium, the temperature rise when the medium vaporizes at the given inlet pressure, and the shaft power at the shut-off point.
The seal wasn’t damaged by impact; instead, the vibration of the pressure buildup pump increased, causing an increase in the temperature of the medium. Vibration should be the main cause
I agree with you; the seal cannot be damaged by pressure. The vibration of the pressure pump increases, along with an increase in the temperature of the medium, and even its vaporization.
Changing the frequency requires replacing the motor as well; inducing backflow consumes electricity, and running the pump at a low flow rate also increases energy use.
The flow rate is set low, which strains the pump; how to put it?
The pump vibrates, and the lifespan of the bearing seals is reduced. If the minimum flow rate cannot be maintained, the temperature rise of the medium can lead to cavitation. If the medium is corrosive, the corrosion rate doubles for every 10-degree increase in temperature
In your case, installing a frequency converter on the pump is the best option, and there’s no need to replace the motor. Variable-frequency motors are used in variable-frequency speed control processes to ensure that the cooling fan of the motor does not slow down at low speeds. When a regular motor is equipped with an inverter, in order to prevent the motor from overheating at low speeds, it is possible to set a minimum frequency on the inverter (we set it at 30 hertz). There are many advantages to installing a frequency converter on a water pump. One of them is that the soft start function of the frequency converter helps to extend the lifespan of various components of the pump.
Foam, I’m sending you a picture; please help analyze it. It’s the side near the impeller, where water is dripping
Thank you very much. I initially thought that variable frequency meant saving energy by reducing the starting current, so as to avoid excessively high starting currents. But my current problem is that the outlet opening is too small; at the section near the impeller, there is severe leakage. Could it be that the pressure in the pump chamber is too high, causing the leakage? As for changing the frequency, does that mean both the rotational speed and pressure change, so that the pressure becomes lower, right?