Can the pump be held under pressure when its outlet is open?

By overload, they probably mean motor overload; pumps all have their rated pressure and current values, and as long as the pressure and flow rate meet those specifications, it’s fine.

This is related to the outlet diameter designed by your factory; if the diameter is too large, the opening degree of the outlet valve has a significant impact on the flow rate. As the flow rate increases, the motor current also increases. Once the flow rate reaches 120% of the rated value, the motor is operating under overload conditions, which can easily lead to motor damage. Therefore, overcurrent protectors are usually installed in the circuit to protect the motor when excessive current is detected. Flow rate and current are directly proportional to each other; as the valve is opened wider, the flow rate necessarily increases. The diameter of the pipe is directly related to the medium; for flammable and explosive media, the pipe diameter is several times larger than that of the pump outlet. It is mainly to limit the flow rate of the conveyed medium in order to prevent the generation of static electricity. Given that your pump is a magnetic drive pump, its optimal operating range is 60%-120% of the rated flow rate; it is necessary to keep the pump operating within this range. The minimum flow rate should not be less than 30% of the rated flow rate, as operating at low flow rates leads to heat accumulation, which reduces the lifespan of the carbonized (silicon) bearings. When the temperature exceeds 380 degrees, it is possible to damage the internal magnet (in some cases, the internal magnet can withstand temperatures of 500–600 degrees), resulting in significant losses. Taking all these factors into account, it is best to determine the operating flow rate during operation; magnetic pump requirements regarding flow rate are higher than those of ordinary centrifugal pumps. Do not judge whether it is operating under optimal conditions solely based on the opening degree of the outlet valve. Some designed pipelines are equipped with flow-limiting devices, and there are also those with self-regulating valves at the rear end; in such cases, even if you open the valves fully, the flow rate will not increase. It is necessary to understand certain processes in order to operate the equipment more effectively.

It refers to motor overload; generally, when a pump starts, the starting current of the motor is several times the rated current. If the outlet valve is not closed and flow increases, the starting current will be higher, which may damage the motor. When starting the positive displacement pump, in order to prevent pressure buildup at the outlet, it is necessary to keep the outlet valve fully open; however, to avoid overloading the motor, the pump’s stroke must be set to zero. After the pump starts, increase its speed gradually according to the process requirements.

When the outlet valve is opened too wide, the flow rate increases, and the motor will definitely be overloaded. We have a pump whose outlet pipe is too large; as a result, the valve can only be turned 2-3 turns during use, and there is a lot of noise. Therefore, pipeline design is also very important.

If the pump’s output flow exceeds the rated flow, the motor current will exceed the rated value. What your technicians said is correct; however, it’s necessary to figure out what the appropriate flow rate at the pump outlet should be, and this can be determined using instruments to measure the flow.