Use, repair, and assembly of hydraulic pumps

1.What should I pay attention to when using gear pumps?
① The oil suction height of gear pumps should generally not exceed 500mm.
② The gear pump should be directly connected to the motor through a flexible coupling. Generally, it should not be rigidly connected or connected to the power source through gear pairs and belt mechanisms to avoid unilateral force, causing bending, unilateral wear, and failure of the pump shaft oil seal.
③ The limit speed of the gear pump should be limited and cannot be too high or too low. If it is too high, the oil cannot fill the entire gap between the teeth in time, which can cause cavitation, vibration, and noise; If it is too low, it cannot create the necessary vacuum in the pump oil suction chamber, which can cause poor oil suction. At present, the driving speed of domestic gear pumps is between 300-4450r/min, as detailed in the gear pump user manual.
④ When selecting, gear pumps are mostly unidirectional pumps, divided into left pump and right pump. Pay attention when purchasing, otherwise when using in reverse, oil cannot be applied or the oil quantity is insufficient, and it often causes the pump shaft oil seal to flip and break. If you need a bidirectional rotary pump and a reverse pump, you need to place a special order.

⑤ General gear pumps use YA-N46 (GB 2512-1981) ordinary hydraulic oil, with a working oil   temperature controlled at 0-80 ℃   and a   filtration accuracy of 25 μ About m.
After using the gear pump for a long time, the relative sliding surfaces of the gears will experience wear and scratches. The wear of the end face will lead to an increase in axial clearance and internal leakage; The wear of the tooth tip circle can lead to an increase in radial clearance; Tooth wear can cause increased noise and pressure oscillation. When the wear and tear are not severe, they can be slightly ground (ground) and polished before use. If the wear and tear are severe, they need to be repaired or replaced according to the situation.

2.How to repair gears and gear shafts?
The wear part of the gear pump shaft (gear shaft) is mainly at the journal that comes into contact with the needle bearing or shaft sleeve. If there is slight wear, it can be polished and repaired. If the wear is severe, it is necessary to use chrome plating process or remachine a new shaft. When remachined, the coaxiality of the two journals is 0.02-0.03mm. The coaxiality of the gear installed on or connected to the shaft is 0.01mm.
① Tooth shape repair
Use a fine sandcloth or oilstone to remove the burrs on the raised or ground polygonal parts, and then install the gear coaxially on the bearing hole of the pump cover for grinding. Use the red lead coating method to verify the grinding effect. Properly change the orientation of the meshing surface and continue to use it after cleaning. However, for severely worn parts that can be observed with the naked eye, gears should be remade and replaced.

② End face repair
For slight wear, both gears can be sanded on a 0 # abrasive cloth at the same time, and then polished on a metallographic abrasive paper. When the wear and tear are severe, the two gears can be simultaneously ground on a flat grinder to remove a small amount, and then ground or polished with metallographic sandpaper. At this point, the pump body should also be ground to the same size to ensure the original assembly clearance (0.02-0.03mm). The thickness difference between the two gears should be within 0.005mm, and the perpendicularity between the gear end face and the hole or the runout of the gear axis should be controlled within 0.005mm.
③ Addendum circle
External gear pumps, due to the presence of radial imbalance, generally experience wear after use for a period of time. After the tooth tip circle is worn, the radial clearance increases. For low-pressure gear pumps, internal leakage will not increase much. However, for medium and high pressure gear pumps, which may have an impact on volumetric efficiency, electroplating the outer circle (brush plating the tooth top circle) or replacing the gear should be considered.
④ The gear accuracy of the medium and low pressure gear pump is 7-8 levels, while the gear accuracy of the medium and high pressure gear pump is slightly higher by 0.5-1 levels. The coaxiality tolerance between the gear inner hole and the tooth top circle (for the gear shaft, the tooth top circle and the journal outer circle) is<0.02mm, the non parallelism of the two end surfaces is<0.007mm, and the surface roughness is.

⑤ Gear shaft
If the surface of the gear shaft connected to the shaft is peeled off or burnt or discolored, a new gear shaft should be replaced; If the surface is gray white and only the fit gap increases, the position of the meshing teeth can be adjusted appropriately and a new bearing can be replaced; If the surface of the gear outer circle is roughened due to cleaning, and there are iron chips stuck on the top of the teeth, the adhesive can be removed with an oil stone sand strip, and the joint surface of the pump inner hole can be sanded. If the radial clearance does not exceed the tolerance, it can be continued to use. If the radial clearance is too large, the pump inner hole can be plated with copper alloy according to the situation to reduce the radial clearance.

3.How to repair the pump body, front and rear covers, shaft sleeves, and side plates?
The wear of the pump body mainly occurs on the inner cavity surface (the surface in contact with the tooth tip circle - G6 surface), and it mostly occurs on the oil suction side. If the pump body is symmetrical, the pump body can be flipped 180 ° for installation and reuse. If it is an asymmetric type, it is necessary to use the electroplating bronze alloy process or brush plating method to repair the worn parts of the pump body cavity holes.
The main parts for repairing the front and rear covers and shaft sleeves are the end faces that come into contact with the gears. When the wear is not severe, the end face can be repaired by grinding on a flat plate. When the wear and tear are severe, the grooves can be removed on a surface grinder first, and then slightly ground. However, it is necessary to deepen and widen the relevant dimensions of the unloading groove appropriately.
After the side plates are worn, they can be placed on a grinding plate or glass plate, and ground flat with 1200 # diamond sand. The surface roughness should be lower than Ra0.8, and the thickness difference should not exceed 0.005mm within the entire circle range.

4.How to assemble a gear pump?
When assembling a repaired gear pump, the following precautions must be taken:
① Remove burrs from all parts. The sharp edges of the gears should be blunted with natural oilstone, but they should not be rounded. The parts that have been flat ground should be demagnetized. All parts must be carefully cleaned with kerosene before being put into assembly.
② Measure and ensure the axial clearance during assembly: the axial clearance of the gear pump δ= Pump body thickness L0- gear width L1, generally ensuring δ Measure the relevant dimensions and accuracy of other parts between 0.02-0.03mm.
③ When assembling gear pumps, some gear pumps have positioning pin holes. For gear pumps without positioning holes, during assembly, tighten the screws diagonally while rotating the pump shaft. If there is no difference in weight, tighten several installation screws thoroughly. For gear pumps with positioning holes (such as CB-B type), pin holes are mainly used in the machining process of parts, so there is no positioning reference during assembly. Finally, two pin holes are drilled and reamed to drive in the positioning pin.

④ For parts that are easily reversed, be careful not to install them in the wrong direction. Especially to confirm whether it is a forward or reverse pump.
⑤ Oppose using a paper pad between the pump body and pump cover to solve the problem of external leakage. A layer of paper should be at least 0.06-0.1mm thick, which will seriously affect the axial clearance and increase internal leakage. In severe cases, the gear pump cannot be oiled.
⑥ If conditions permit, the gear pump can be bench tested according to JB/T 7041-1993 and other standards before being installed into the main engine.