Jiangsu Zhongyi Work Rigging Co., Ltd. , https://www.zy-rigging.com
To enhance the service life and operational safety of shielded pumps, they are typically equipped with several protective systems. (1) Bearing Wear Monitor: This device is generally categorized into mechanical, electromechanical, electrical, and electronic types based on its detection method. During operation, the bearing wear monitor continuously tracks the condition of the bearing. If excessive wear is detected, the pump should be stopped or repaired, and the bearing may need to be replaced. In case of sudden bearing failure during operation, immediate shutdown is necessary. Pipeline-based mechanical monitoring is the most direct and reliable but lacks adjustability and early warning capabilities. Other types of monitors can provide on-site display and output 4–20mA signals as well as alarm switches. The latest model shown in Figure 2-15 is an electronic bearing wear monitor.
(2) Current Protection: In the event of dry running, a shielded pump can suffer serious damage. When the flow rate drops significantly, the current will also decrease considerably. At this point, the current protection system sends a control signal via the user's protective device to stop the pump and prevent accidents. Similarly, if a magnetic pump experiences excessive load, the current increases, triggering the current protection mechanism to automatically cut off power and stop the motor, thus avoiding potential failures.
(3) Motor Over-Temperature Protection: A temperature sensor is pre-installed in the stator’s three-phase windings to trigger an over-temperature alarm. This helps prevent the motor winding temperature from exceeding its insulation limits and ensures compliance with explosion-proof requirements. Temperature sensors are mainly divided into three types: thermistors (PTC), thermal switches, and resistance temperature detectors (such as PT100). Thermistors and thermal switches are low-cost and widely used, but they are binary-controlled, with non-adjustable alarm temperatures. Resistance temperature sensors, on the other hand, allow real-time monitoring through a display instrument and are commonly used in critical pump positions or special winding configurations.
In addition to these three protections, shielded pumps can also be equipped with heat exchange capacity monitors, liquid level monitors, or internal pressure protectors within the motor, depending on the specific application requirements. These additional features help ensure comprehensive safety for various operating conditions.