The working principle of the centrifugal pump is:
The centrifugal pump can send water out because of the role of centrifugal force. Before the pump works, the pump body and the water inlet pipe must be filled with water to form a vacuum state, when the impeller rotates rapidly, the blade promotes the rapid rotation of water, the rotating water flies away from the impeller under the action of centrifugal force, after the water in the pump is thrown out, the central part of the impeller forms a vacuum area. The water from the source is pressed into the inlet pipe through the pipe network under the action of atmospheric pressure (or water pressure). In this way, continuous pumping can be achieved.
The main components of the centrifugal pump are impeller, pump body, shaft seal device, sealing ring, packing box:
1. Impeller:
The impeller is the core part of the centrifugal pump, it has high speed and large output force, and the blade on the impeller plays the main role. The impeller should pass the static balance experiment before assembly. The inner and outer surfaces on the impeller should be smooth to reduce the friction loss of the water flow. The impeller generally has 6 to 12 backward-curved blades. The impeller has three types: open, semi-closed and closed. The open impeller has no cover plate on both sides of the blade, which is simple to manufacture and easy to clean. It is suitable for conveying materials containing a large number of suspended substances, with low efficiency and low liquid pressure. The semi-closed impeller has no cover on the suction side and a cover on the other side, which is suitable for conveying materials that are easy to precipitate or contain particles, and the efficiency is also low; The closed impeller has front and rear cover plates on both sides of the blade, which is of high efficiency and suitable for conveying clean liquid without impurities. The general centrifugal pump impeller is mostly of this kind.
2. Pump body:
The pump body is also called the pump shell, which is the main body of the pump. It plays the role of supporting and fixing, and is connected with the bracket for mounting bearings. The function is to seal the impeller in a certain space in order to inhale and press out the liquid by the action of the impeller. The pump shell is made of volute shape, so it is also called volute. As the cross-sectional area of the flow channel gradually expands, the high-speed liquid thrown from the impeller around the flow rate gradually reduces, so that part of the kinetic energy is effectively converted into static pressure energy. The pump housing not only collects the liquid thrown out by the impeller, but also serves as an energy conversion device.
3. Shaft seal device:
The function is to prevent the liquid in the pump casing from leaking out along the axis or the outside air from leaking into the pump casing. Commonly used shaft sealing devices include packing seals and mechanical seals. Packing is usually asbestos rope impregnated with oil or coated with graphite. The mechanical seal mainly relies on the relative movement of the end face between the dynamic ring installed on the shaft and the static ring fixed on the pump housing to achieve the purpose of sealing.
4, sealing ring:
Sealing ring is also called leakage reducing ring. The clearance between the inlet of the impeller and the pump casing is too large, which causes the water in the high pressure area of the pump to flow to the low pressure area through this gap, affecting the water output of the pump and reducing the efficiency! Too small clearance will cause friction between impeller and pump casing and wear. In order to increase the backflow resistance and reduce internal leakage, delay the service life of the impeller and the pump shell, the sealing ring is installed at the inner edge of the pump shell and the outer aid of the impeller, and the sealing gap is maintained between 0.25 and 1.10mm.
5, stuffing box:
The packing box is mainly composed of packing, water seal ring, packing barrel, packing gland and water seal tube. The function of the stuffing box is mainly to close the gap between the pump shell and the pump shaft, so that the water in the pump does not flow outside and does not allow the outside air to enter the pump. Always maintain the vacuum in the pump! When the pump shaft and the packing friction generate heat, it is necessary to rely on the water seal pipe to inject water into the water seal ring to cool the packing! Keep the pump running properly. Therefore, special attention should be paid to the inspection of the stuffing box during the operation of the pump. The filler should be replaced after about 600 hours of operation.
6, the axial force balancing device in the centrifugal pump operation process, because the liquid is at low pressure into the impeller, and at high pressure out, so that the pressure on both sides of the impeller is unequal, resulting in the axial thrust pointing to the direction of the entrance, will cause the rotor axial movement, wear and vibration, so the axial thrust bearing should be set up in order to balance the axial force.