Troubleshooting methods for common faults of gear pumps

At present, CB-B gear pump is widely used in dump trucks and construction machinery control mechanisms, and its common faults and troubleshooting methods are introduced as follows for reference.
1. Causes and elimination of vibration and noise
(1) Inhale air
(1) The pump body of CB-B gear pump and the end cover on both sides are hard seals in direct contact, if the flatness of the contact surface does not meet the specified requirements, the pump is easy to suck air during work; Similarly, the end cover of the pump is in direct contact with the gland and air is easy to invade; If the gland is a plastic product, due to its damage or deformation due to temperature changes, it will also make the seal not tight and enter the air. The method to eliminate this fault is: when the flatness of the pump body or pump cover does not meet the specified requirements, it can be ground back and forth with gold steel sand on the plate according to the "8" figure-shaped route, or it can be ground on a plane grinder so that its flatness does not exceed 5μm, and it is necessary to ensure the perpendicularity of its plane and the hole; Leaks at the pump cover and gland can be sealed with an adhesive such as epoxy resin.
(2) The pump shaft is generally sealed with a skeleton type oil seal. If the spring that clamps the lip falls off, or the oil is encapsulated backwards, or the lip is strained and aged, the rear end of the oil seal is often in a negative pressure state and air is inhaled, and the new oil seal can generally be replaced to solve it.
(3) The amount of oil in the oil tank is not enough, or the oil suction pipe mouth is not inserted below the oil surface, the pump will suck in air, and the oil should be replenished to the oil tank to the oil marking; If the oil return pipe mouth is exposed, sometimes the air will be backfilled into the system due to the instantaneous negative pressure in the system, so the oil return pipe mouth should generally be inserted below the oil surface.
(4) The installation position of the pump is too high from the oil surface, especially when the pump speed is reduced, because the necessary vacuum degree of the pump suction chamber cannot be guaranteed to cause insufficient oil absorption and suck air. At this time, the relative height of the pump and the oil level should be adjusted to meet the specified requirements.
(5) The oil suction filter is blocked by dirt or its capacity is too small, resulting in increased oil absorption resistance and air inhalation; In addition, the large diameter of the oil inlet and outlet may also bring in air. At this time, the oil filter can be cleaned, or a larger capacity oil filter with appropriate inlet and outlet diameter can be selected. This prevents not only air inhalation, but also noise.
(2) Mechanical reasons
(1) The connection between the pump and the coupling produces vibration and noise due to non-compliance with the requirements. The coupling should be adjusted according to the specified requirements.
(2) Noise caused by the wear and strain of gears and other components caused by dirt in the oil entering the pump. The oil should be replaced, the filtration should be strengthened, and the pump should be disassembled for cleaning; Gears with severe wear must be repaired or replaced.
(3) Serious damage or wear of the parts in the pump will produce vibration and noise: such as tooth shape error or circumferential error, poor contact between the two gears, high roughness of the tooth surface, abnormal length of the common normal, too small tooth backlash, and the contact area of the two meshing gears is not in the index circle position. At this point, the gear can be replaced or the gear can be sharpened. At the same time, the needle roller cage of the bearing is damaged, the long and short shaft journal and the needle roller wear can lead to poor bearing rotation and mechanical noise, at this time, it is necessary to disassemble and repair the gear pump and replace the needle roller bearing.
(4) The gear axial assembly clearance is too small; The sliding joint surface between the gear end face and the front and rear end cover cannot be carefully removed due to the burr of the gear before assembly, so that the joint surface is strained during operation, so that the internal leakage is large, resulting in a decrease in output flow; Dirt enters the pump and wedges into the gap between the gear end face and the front and rear end covers, which causes the high and low pressure chambers to connect due to the groove of radial strain, so that the output flow is reduced. The above situation should be repaired by the following measures respectively. Disassemble the gear pump and appropriately increase the axial clearance, that is, the end face of the grinding gear; Smooth the front and rear cover end faces and gear end faces with a surface grinder, and remove burrs (not chamfering) on the teeth; After surface grinding, the depth dimension of the unloading groove on the end face of the front and rear cover after surface grinding will change, and the width should be appropriately increased.