What is the working principle of a screw pump?
The principle of lifting water with a screw pump is different from that of a vane pump and a volumetric pump. It is a special form of lifting equipment, and its working principle is shown in Figure 7-8. The spiral is tilted and placed in the pump slot, with the lower part of the spiral submerged underwater. Due to the inclination angle of the spiral shaft to the water surface being smaller than that of the spiral blades, when the spiral pump rotates at low speed, water enters from point P of the blades. Then, under the action of gravity, it descends to point p with the blades, and the inertial force generated by the rotation lifts the water at point p to point R. Then, under the action of gravity, the water descends to the bottom of the higher-level blades. The water continuously circulates and rises up the spiral shaft step by step, finally reaching the highest point of the spiral pump slot and flowing out.
What are the components of a screw pump? What are the functions of each part?
The screw pump mainly consists of five parts and auxiliary equipment, including the screw part, lower bearing, upper bearing, driving device, and pump groove.
(1) The spiral part is the main body of the spiral pump, usually composed of welded steel blades outside the central steel pipe. The diameter of the steel pipe is usually about 1/2 of the outer diameter of the spiral, and the thickness of the blades is 5-10mm. In order to prevent corrosion, the blades can be made of stainless steel material. The blades are made of three head or double head spiral, usually rotating at a speed of 30-120r/min, forming a continuously rising sealing area with the pump groove to achieve the purpose of lifting sludge or sewage.
(2) The lower bearing is submerged in sewage and is therefore also known as a water bearing, bearing 1/2 of the radial load. The bearing seat is a sealed housing that houses a radial ball bearing. The shell is filled with lubricating grease, and there are sealing gaskets and packing boxes on the upper part to prevent the infiltration of sewage and mud. Mechanical seals are also used to protect the bearings. To prevent the impact caused by thermal expansion and contraction in the length direction of the spiral, the bearing bracket is floating.
(3) The upper bearing works completely above the water surface, consisting of a shell and radial ball bearings
(4) Spiral pumps have a simple structure and do not require auxiliary machinery such as vacuum pumps or lubrication cooling water pumps. The spiral blades are installed open, making maintenance and repair very convenient. Impurities smaller than the pitch can pass through without being blocked by sludge. The screw pump has a low rotational speed, which prevents cavitation of high-speed pumps, and has minimal wear. Even if there is wear, it is easy to repair, resulting in a long service life and high reliability. Improving the transportation of sludge will not damage the integrity of activated sludge flocs, which is beneficial for the activity of the returned sludge entering the aeration tank.
(5) The disadvantages of spiral pumps are large volume and low head, which are not suitable for high head pump stations and situations with large water level changes. The outlet side cannot be equipped with pressure pipelines, and can only be open channels or gravity flow pipelines. It must be installed at an angle, and the pump body has a large volume, so it occupies a large area, and the tank body is open, which makes it easy to evaporate odors.
What are the precautions for the use and maintenance of screw pumps?
(1) Efforts should be made to ensure that the suction position of the screw pump operates at or above the standard point specified in the design. At this time, the pumping capacity of the screw pump is the design flow rate. If it is lower than the standard point, even if it is only a few centimeters lower, the pumping capacity of the screw pump will decrease significantly.
(2) When the screw pump is not in use for a long time, if it is not moved for a long time, the downward deflection of the long screw part of the screw pump will be permanent, which will affect the gap between the screw and the pump groove and the dynamic balance of the screw part. Therefore, the screw should be rotated by a certain angle at regular intervals to offset the adverse effects caused by deflection in one direction.
(3) The spiral part of the screw pump mostly works outdoors. Before starting the screw pump in winter in the north, it is necessary to check whether the suction tank is frozen and whether the spiral part is frozen with the pump groove. Before starting, the accumulated ice should be removed to avoid damaging the driving device or the blades of the screw pump.
(4) Ensuring the accurate and uniform clearance between the blades and the pump slot of the screw pump is the key to ensuring efficient operation of the screw pump. It is necessary to regularly measure whether the clearance between the screw pump and the pump slot during operation is between 5-8mm and adjust it to a uniform and accurate level. Pay attention to abnormal changes in the sound of the screw pump during inspection, such as the sound of steel plates scraping on the ground when the screw blades rub against the pump groove. At this time, the pump should be stopped immediately to check for faults and adjust the clearance. When the upper bearing malfunctions, it will also make abnormal noises and the bearing housing will heat up. Attention should also be paid during inspection.
(5) Due to the fact that screw pumps are usually 30. Tilt installation, the drive motor and gearbox must also be tilted, which will affect the lubrication effect of the gearbox. Therefore, when refueling the gearbox, the oil level should be slightly higher than the normal oil level. If there is no oil drain port at the lowest point during oil discharge, efforts should be made to extract the remaining oil.
(6) Regularly add lubricating oil to the upper and lower bearings, and observe for oil leakage when adding oil to the lower bearing. If any leakage is found, empty the suction tank and tighten the packing or replace the failed sealing gasket. Even in the absence of any issues, it is necessary to regularly empty the suction tank and run the vehicle empty to check if the underwater bearings are functioning properly.
