Because of its variable pump delivery, self-priming capability, reversible, capable of conveying liquids containing solid particles and other characteristics, in sewage treatment plants, is widely used in the transport of water, sludge and flocculant liquid chemicals . Screw pump selection should follow the economic, reasonable and reliable principles. If the design selection of ill-considered, will give future use, management, maintenance trouble, so choose a production according to actual needs, reasonable and reliable screw pump can ensure the smooth production, but also reduce repair costs. First, the speed of the screw pump selection Screw pump flow and speed into a linear relationship, relative to the low-speed screw pump, high-speed screw pump while increasing the flow and lift, but significantly increased power, high speed accelerated the rotor and Stator wear, the screw will inevitably lead to failure, and high-speed screw rotor rotor length is very short, easy to wear, thus shortening the life of the screw pump. Through the speed reducer or stepless speed regulating mechanism to reduce the speed, the speed maintained at a reasonable range of three hundred revolutions per minute, and high-speed operation of the screw pump, the service life can be extended several times. Second, the quality of the screw pump Now on the market more types of screw pump, relatively speaking, the imported screw pump design, excellent material, but the higher prices, some services are not in place, parts prices, ordering Long cycle, may affect the normal operation of production. Most of the domestic production of imported products imitation, product quality varies greatly in the choice of domestically produced products, considering its cost-effective time, the choice of low speed, long lead, transmission parts of good quality, long life rating of the product. Third, to ensure that debris does not enter the wet mud sludge mixed with solid impurities will screw the rubber material stator damage, so to ensure that debris does not enter the cavity of the pump is very important, many sewage treatment plant before the pump Installed a grinder, and some grille installation or filter, blocking debris into the screw pump, grill should be promptly salvaged to avoid clogging. Fourth, to avoid broken screw pump Never run in the case of broken material, once occurred, the rubber stator due to dry friction, instantaneous heat generated and burned, so the grinder intact, smooth grille is necessary for the normal operation of the screw pump One of the conditions, therefore, some screw pump is still installed in the pump body break down device, when there is a broken material, due to the self-priming screw pump has the characteristics of the cavity will produce a vacuum, the vacuum device will stop the screw pump Run. Fifth, to maintain a constant outlet pressure Screw pump is a positive displacement rotary pump, when the outlet end is blocked, the pressure will gradually increase, so that the pressure exceeds the predetermined value. At this time the motor load increased dramatically. Transmission machinery related parts load will exceed the design value, severe motor burn occurs, the transmission parts broken. In order to avoid damage to the screw pump, generally installed at the outlet of the screw pump bypass relief valve to stabilize the outlet pressure to maintain the normal operation of the pump.