At present, centrifugal pumps are mostly used in car engines. It is mainly composed of a fixed cast iron (or cast aluminum) shell and a rotating impeller mounted on the shaft. The impeller is usually radial or backward bending, the number of which is generally 68. When the impeller rotates, the water in the pump is driven by the impeller to rotate together, and under the action of its own centrifugal force, it throws out to the edge of the impeller, and then is pressed into the engine water jacket through the outlet pipe tangential to the impeller on the shell. Pump impeller blade rupture or loosening; water seal washer and rubber washer wear and damage; screw hole thread damage and bearing loose. Before decomposing the pump, it is necessary to heat the pump in the hot water heating vessel to about 80 C, so as to facilitate decomposition.

Inspection of the pump shell and pulley without damage, minor damage can be repaired, serious damage should be replaced. When the flatness error of the joint surface between pump shell and cover and between shell and cylinder block exceeds the limit value, it should be milled flat. After repairing, the verticality error of the joint face between shell and cover is 0.05 mm. When there are grooves and pits on the water seal joint surface in the pump shell, reamer reamer pin is used to smooth it. Overwear can be repaired by inserting flanged sleeves. If the screw thread on the pump shell is damaged, the screw thread can be tapped out after enlarging the hole diameter or after welding repair.

Check whether the pump shaft is bent, whether the journal wear exceeds the limit value, and whether the end threads are damaged. When the bending of the pump shaft is greater than 0.05 mm, the bending value should be corrected by cold pressure. The bending value is about 5 times that of the radial circular jumping value, and it should stay for 2 minutes. After correction, the radial circular jumping value should be less than 0.10 mm. If the pump journal wears out of circle, it should be repaired by polishing and chromium plating or iron plating. The fit clearance between pump shaft and bearing inner ring is generally 10.02+0.04 mm. When the clearance is larger than 0.03 mm, the journal can be repaired by electroplating.

When the bearing is loose, if the axial clearance is greater than 0.30 mm and the radial clearance is greater than 0.15 mm, a new bearing should be replaced. Bearing seat holes are often worn by sub-human and extruded bearings. When the wear of bearing seat holes exceeds 0.03 mm, it can be repaired by insertion method. The fit between bearing and bearing holes is generally 10.02+0.04 mm.

Check the wear and damage degree of water seal rings, bakelite pads, springs and other parts. If there is damage or damage, it should be replaced. Water seal assemblies should be replaced during overhaul of pumps. Check the matching of pulley hub and pump shaft. The hole of the pump shaft is worn out too much and can be repaired by inlay. Check the wear condition of the key groove of the pump shaft and the belt wheel. After welding and repairing, the key groove can be milled by milling machine or re-opened on the milling machine at the position of 90 180 angle separated from the old key groove. If fan clutch is installed, oil leakage shall be checked. Clutch assembly should be replaced if leakage occurs.

The bearing of the pump and the bearing hole of the pump shell are generally 10.02 mm and 10.020.04 mm for overhaul. Pump shaft with impeller bearing hole, without fixed stud (nut), is generally 10.04-10.01 mm; with fixed nut, is generally 10.02+0.05 mm. When the impeller of the pump is assembled, it should generally be 0.10.5 mm higher than the pump shaft. When the pump is assembled, there should be a gap of 0.75100mm between the impeller and the pump cover. The gap between the outer edge of the impeller and the inner cavity of the chestnut shell is generally about 1mm. Pump shaft and fan pulley hub, without fixed bolts (nuts), is generally 10.04-10.01 mm; with fastening bolts (nuts), is generally 10.02+0.06mm. The bolts and nuts should be tightened according to the prescribed moment, and the locking should be reliable. The drain hole under the pump body should be unblocked. After the pump is boxed, the pump shaft shall be filled with a specified brand of grease. Pumps are tested on test bench. When the pump shaft runs at a speed of 1000 r/min, the displacement per minute should not be lower than the prescribed value. There should be no metal friction and water leakage in the test of 10min. In the engine test: during the test, no thermostat is installed, the water return pipe of the water tank is removed, and the engine is started, so that the speed of the engine reaches about 2000 r/min, and the water is discharged into the measuring cylinder to check whether the drainage basically meets the requirements. If the difference of drainage is too large, the cause should be checked and eliminated. If there is no flow tester, the pump shell inlet can be blocked, and then water is added to the pump. When rotating the pump shaft, there should be no water leakage from the drain hole.