Application Characteristics And Selection Methods Of Screw Pumps

Apr 02, 2025

Screw pumps are widely used in sewage treatment plants for transporting water, wet sludge, and flocculant solutions due to their variable conveying capacity, strong self-priming ability, reversibility, and ability to transport liquids containing solid particles. The selection of screw pumps should follow the principles of economy, rationality, and reliability. If the design and selection are not carefully considered, it will bring trouble to future use, management, and maintenance. Therefore, choosing a reasonable and reliable screw pump according to actual production needs can ensure smooth production and reduce repair costs.

1. Selection of rotational speed for screw pump

The flow rate and speed of a screw pump are linearly related. Compared to low-speed screw pumps, high-speed screw pumps can increase flow rate and head, but their power is significantly increased. High speed accelerates the wear between the rotor and stator, which inevitably leads to premature failure of the screw pump. Moreover, the length of the stator and rotor of high-speed screw pumps is very short, which is prone to wear and tear, thus shortening the service life of the screw pump. By using a reducer or a continuously variable speed mechanism to reduce the speed and keep it within a reasonable range of less than 300 revolutions per minute, the service life can be extended several times compared to high-speed screw pumps.

2. Quality of screw pump

There are many types of screw pumps on the market now. When selecting products, when considering the cost-effectiveness of screw pumps, choose products with low speed, long lead, excellent transmission component materials, and long rated life.

3. Ensure that debris does not enter the pump body

The solid debris mixed in wet sludge can cause damage to the rubber stator of the screw pump, so it is important to ensure that the debris does not enter the pump chamber. Many sewage treatment plants have installed crushers before the pump, and some have installed grid devices or filters to prevent debris from entering the screw pump. The grid should be cleaned up in a timely manner to avoid blockage.

4. Avoid material breakage

Screw pumps are never allowed to operate in the event of material breakage. Once this occurs, the rubber stator will instantly generate high temperatures due to dry friction and burn out. Therefore, the integrity of the crusher and the smoothness of the grille are necessary conditions for the normal operation of screw pumps. Therefore, some screw pumps also install a material breakage shutdown device on the pump body. When material breakage occurs, due to the self-priming function of the screw pump, a vacuum will be generated in the chamber, and the vacuum device will stop the screw pump from running.

5. Maintain a constant outlet pressure

Screw pump is a type of positive displacement rotary pump. When the outlet end is blocked, the pressure gradually increases to exceed the predetermined pressure value. At this point, the motor load increases sharply. The load on transmission machinery related components may also exceed the design value, and in severe cases, motor burnout and transmission component fracture may occur. In order to avoid damage to the screw pump, a bypass overflow valve is usually installed at the outlet of the screw pump to stabilize the outlet pressure and maintain the normal operation of the pump.