What Is a Progressive Cavity Pump?

Screw pump, also known as "spiral pump", "Archimedean screw pump". A type of pump that uses the rotation of spiral blades to make the water body spiral upward in the axial direction. It consists of a shaft, a spiral blade and a casing. When pumping water, the pump is placed obliquely in the water, so that the inclination of the main shaft of the pump is smaller than the inclination of the spiral blade, and the lower end of the spiral blade is in contact with water. When the prime mover drives the screw pump shaft to rotate through the speed change device, water enters the blades and rises along the spiral flow channel until it flows out. The structure is simple, the manufacturing is easy, the flow is large, the head loss is small, the efficiency is high, and it is easy to repair and maintain, but the head is low and the rotation speed is low. Mostly used for irrigation, drainage, and upgrading sewage and sludge. China has been using it since the 1970s. ^[1]

The screw pump device includes a prime mover, a variable speed transmission, and a screw pump, as shown in Figure 1. Specifically, the screw pump consists of a screw blade 1, a pump shaft 2, and a bearing seat.

(1) Mounting angle (). The installation inclination angle refers to the angle between the screw pump shaft and the horizontal plane. It directly affects the efficiency and flow of the pump. According to relevant data, each increase of the inclination angle reduces the efficiency by about 3%. It is generally considered economical to have an inclination angle of 30 ° to 40 °.

(2) Clearance. Clearance refers to the clearance between the spiral blade and the housing. The smaller the gap, the smaller the water loss and the higher the efficiency of the pump.

(3) Speed (n). The speed of the screw pump is relatively slow, generally 20 80 r / min. Experimental data proves that when the outer diameter of the screw pump is large, the speed should be reduced.

(4) Lifting height (H). The screw pump only has a lifting height, but not a pressure water height. Its lifting height is generally 3 to 8 m.

(5) Diameter of spiral blade (D). The larger the blade diameter of the pump, the higher its efficiency. The optimal ratio of the blade diameter of the screw pump to the diameter of the pump shaft is 2: 1.

(6) The number of heads (Z). The number of heads refers to the number of spiral blades, and is generally 1 to 4 pieces. They are spirally raised around the pump shaft at a certain interval. The more heads, the higher the pump efficiency. For a certain diameter screw pump, the lifting capacity increases by about 20% for each additional blade head.

(7) Lead and pitch. The axial distance through which the spiral blades spirally rise 360 ° around the pump shaft is a lead .

Compared with vane pumps, screw pumps have the following advantages:

Screw pumps are divided by the number of screws.

1. The pump body vibrates violently or generates noise:

cause:

Screw pumps are widely used in the transportation of water, wet sludge and flocculant chemicals in sewage treatment plants because of their characteristics of variable delivery, strong self-priming ability, reversibility, and the 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 is not considered carefully, it will cause troubles in future use, management, and maintenance. Therefore, selecting a reasonable and reliable screw pump according to the actual needs of the production can ensure smooth production and reduce repair costs.

First, the selection of the speed of the screw pump

The screw pump's flow rate and linear speed are linear. Compared with low speed screw pumps, although high speed screw pumps can increase the flow and head, the power is significantly increased. High speeds accelerate the wear between the rotor and the stator. The screw pump fails prematurely, and the stator and rotor length of the high-speed screw pump is very short, which is easy to wear, thus shortening the service life of the screw pump.

The speed is reduced by a speed reduction mechanism or a stepless speed regulation mechanism to keep the speed within a reasonable range of less than three hundred revolutions per minute. Compared with high-speed screw pumps, the service life can be extended several times.

Second, the quality of the screw pump

There are many types of screw pumps. Relatively speaking, imported screw pumps have a reasonable design and good materials, but they have high prices, some services are not in place, high parts prices, and long order cycles may affect the normal operation of production.

Most of the domestic productions are imitations of imported products. The product quality varies greatly. When selecting domestically produced products, when considering their cost performance, select products with low speed, long lead, excellent transmission component materials and long rated life.

Third, ensure that debris does not enter the pump body

The solid debris mixed in the wet sludge will cause damage to the rubber material stator of the screw pump, so it is important to ensure that debris does not enter the cavity of the pump. Many sewage plants have installed a grinder in front of the pump, and some have installed The grille device or filter screen prevents debris from entering the screw pump. The grille should be cleaned in time to avoid blocking.

Avoid material breaks

Screw pumps are never allowed to run under material cuts. Once this occurs, the rubber stator burns out due to dry friction and instantaneous high temperature. Therefore, the crusher is intact and the grid is one of the necessary conditions for the normal operation of the screw pump. Therefore, some screw pumps are also equipped with a material cut-off stop device on the pump body. When a material break occurs, a vacuum is generated in the cavity due to the self-priming function of the screw pump, and the vacuum device will stop the screw pump from running.

Five, maintain a constant outlet pressure

The screw pump is a positive displacement rotary pump. When the outlet end is blocked, the pressure will gradually increase so that it exceeds a predetermined pressure value. At this time, the motor load increases sharply. The load of the related parts of the transmission machinery will exceed the design value. In severe cases, the motor will burn out and the transmission parts will break. In order to avoid damage to the screw pump, an oil return valve is usually installed at the screw pump outlet to stabilize the outlet pressure and maintain the normal operation of the pump. ^[4]