Screw vacuum pumps are widely used in sewage treatment plants for transporting water, wet sludge and flocculant liquid due to their variable transporting capacity, strong self-priming ability, reversibility and ability to transport liquid containing solid particles. Screw vacuum pump selection should follow the principles of economy, rationality and reliability. The application of screw vacuum pump in sewage treatment is introduced as follows:
I. Quality of Screw Vacuum Pump
At present, there are many kinds of screw vacuum pumps on the market. Relatively speaking, the imported screw vacuum pumps are reasonable in design and excellent in material quality, but their prices are higher, some of them are not in place in service, the price of accessories is high, and the ordering cycle is long, which may affect the normal operation of production.
Most of the domestic products are imitations of imported products. The quality of products is uneven. When choosing domestic products, when considering their cost-effectiveness, we should choose products with low speed, long lead, good quality of transmission components and long rated life.
2. Speed Selection of Screw Vacuum Pump
The flow rate of the screw vacuum pump is linear with the speed. Compared with the low-speed screw vacuum pump, the high-speed screw vacuum pump can increase the flow rate and head, but the power is obviously increased. The high-speed accelerates the wear between the rotor and the stator, which will inevitably lead to premature failure of the screw vacuum pump, and the high-speed screw vacuum pump is fixed. The rotor length is very short and easy to wear, thus shortening the service life of the screw vacuum pump.
The speed can be reduced by decelerating mechanism or stepless speed regulating mechanism, so that the speed can be kept within a reasonable range of less than 300 revolutions per minute. Compared with the high-speed screw vacuum pump, the service life can be prolonged several times.
3. Ensure that impurities do not enter the pump body
Solid debris mixed in wet sludge will damage the rubber stator of screw vacuum pump, so it is very important to ensure that debris does not enter the pump chamber. Many sewage plants install crushers before the pump, and some install grille devices or filters to prevent debris from entering the screw vacuum pump. Do not cause blockage.
4.Maintaining a Constant Export Pressure
Screw vacuum pump is a kind of volumetric rotary pump. When the outlet is blocked, the pressure will gradually increase, so that it exceeds the preset pressure value. At this time, the motor load increases sharply. The load of the related parts of transmission machinery will also exceed the design value. In serious cases, the motor will be burnt down and the transmission parts will be broken. In order to avoid the damage of screw vacuum pump, bypass relief valve is usually installed at the outlet of screw vacuum pump to stabilize the outlet pressure and maintain the normal operation of the pump.
5.Avoiding Material Breakage
Screw vacuum pump is never allowed to operate in the case of material breakage. Once it happens, rubber stator will burn out because of dry friction and instantaneous high temperature. Therefore, the crusher is in good condition and the grille is unobstructed, which is one of the necessary conditions for the normal operation of screw vacuum pump. For this reason, some screw vacuum pumps also install material breaking shutdown device on the pump body. When material breakage occurs, due to the self-priming characteristics of the screw vacuum pump, vacuum will be generated in the cavity, and the vacuum device will stop the screw vacuum pump.
In a word, if the design and selection are not considered carefully, it will bring trouble to the future use, management and maintenance. Therefore, choosing a reasonable and reliable screw vacuum pump according to the actual needs of production can not only ensure smooth production, but also reduce the cost of repair.