When screw pumps are used to pump liquids with low liquid levels, they sometimes fail to pump. This is often due to a lack of understanding of the screw pump's suction principle. The main reasons for this are:

1. During initial use, the screw pump was not filled with water or the medium to be conveyed, leading to dry friction and damage to the rubber sleeve. This is one reason why the screw pump may not suck liquid. The solution is to fill the screw pump with liquid from the pump inlet tank before use to maintain lubrication.

2. The suction height during screw pump operation exceeds the allowable suction height range of less than 5 meters. 5 meters refers to media similar to wastewater. For liquids with high viscosity, such as sludge, it is recommended to use a vertical screw pump or various pneumatic diaphragm pumps submerged in the liquid.

3. The screw pump operates on 380V or higher voltage. After wiring, the motor's rotation direction was not checked before use. If the motor is rotating in reverse, simply switch any two of the three power lines.

4. The viscosity of the conveyed medium is too high, such as lime slurry. With screw pumps, a backfilling method is necessary. If backfilling is not possible, a vertical screw pump must be used.