The screw pump applications in sewage treatment

The screw pump is widely used in sewage treatment plant to transport water, wet sludge and flocculant liquid medicine because it has the characteristics of variable transportation, strong self-priming ability, reversibility and the ability to transport liquid containing solid particles. The selection of screw pump should follow the principles of economy, rationality, and reliability. If the screw pump design and selection of screw pump are not considered properly, it will bring trouble to future use, management, and maintenance. Therefore, selecting a reasonable and reliable screw pump according to the actual production needs can not only ensure the smooth production but also reduce the repair cost.

First, the screw pump speed selection

The flow of the screw pump is linearly related to the rotation speed. Compared with the screw pump with low rotation speed, the screw pump with high rotation speed can increase the flow and head, but the power is obviously increased. The high rotation speed accelerates the wear between the rotor and the stator, which will surely lead to premature failure of the screw pump. Moreover, the length of the stator and rotor of the screw pump with high rotation speed is very short and easy to wear, thus shortening the service life of the screw pump.

The speed of the screw pump can be reduced by a speed reduction mechanism or a stepless speed regulation mechanism to keep the speed within a reasonable range of less than 300 revolutions per minute, and the service life of the screw pump can be prolonged several times compared with that of a high-speed screw pump.

Second, the quality of the screw pump

There are many types of screw pumps on the market. Relatively speaking, imported screw pumps are reasonably designed and made of excellent materials, but the price is higher, some of them are not in place in terms of service, the price of accessories is higher, and the ordering cycle is longer, which may affect the normal operation of production.

The quality of the products is mixed. When choosing products from screw pump manufacturer, we should choose products with low rotation speed, long lead, excellent transmission parts, and long rated life when considering their cost performance.

Three, to ensure that debris does not enter the pump body

Solid debris mixed in wet sludge will damage the rubber stator of the screw pump, so it is very important to ensure that debris does not enter the cavity of the pump. Many sewage plants have installed pulverizers in front of the pump, and some have installed grille devices or screens to prevent debris from entering the screw pump. The grille should be cleared in time to avoid clogging.

Fourth, avoid material breaking off

Screw pumps are never allowed to operate under the condition of material broken off. Once they occur, rubber stators burn out due to dry friction and high temperature in an instant. Therefore, one of the necessary conditions for normal operation of screw pumps is that the pulverizer is in good condition and the grille is unblocked. For this reason, some screw pumps have also installed material breakage stop devices on the pump body. When material breaks off, the vacuum will be generated in the cavity due to the self-priming function of screw pumps, and vacuum devices will stop the screw pumps from operating.

Fifth, maintain a constant outlet pressure

The screw pump is a kind of positive displacement rotary pump. When the outlet end is blocked, the pressure will gradually increase to exceed the predetermined pressure value.  At this time, the motor load increases sharply.  The load of the relevant parts of the transmission machinery will also exceed the design value, and the motor will burn down and the transmission parts will break in serious cases.  In order to avoid damaging the screw pump, a bypass relief valve is usually installed at the outlet of the screw pump to stabilize the outlet pressure and maintain the normal operation of the pump.