Common faults of gear oil pumps and troubleshooting methods

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Title: Common Faults of Gear Oil Pumps and Their Solutions Original problem description: Methods for maintaining gear oil pumps； Analysis of the causes of leakage in gear oil pumps. Additional note: A gear pump is a type of pump that transports liquids by utilizing the changes in volume of the working space that occur as two or more gears enclosed within a housing mesh with each other. Haiyou’s summary: A gear oil pump is an essential component that raises the low-pressure oil in the tank to high-pressure oil suitable for performing work, through the mutual rolling engagement of a pair of involute gears with identical parameters and structure. It is a power unit that converts the mechanical energy of the engine into hydraulic energy. Methods for maintaining gear oil pumps: First, gear oil pumps should be lubricated regularly. Electric barrel pumps operate at high speeds, and the lubricant tends to evaporate quickly; therefore, it is essential to keep the lubrication at the bearings clean and to replace the lubricant as needed. Second, gear oil pumps should be regularly inspected and maintained; electric drum pumps also need to be checked regularly. For Roots oil pumps, it is necessary to examine the power cable: whether the internal wiring plugs and switches are in good condition, whether the insulation resistance is normal, whether the brush holders are loose, whether the contact between the commutator and brushes is satisfactory, whether there are any improper connections in the armature windings and stator windings, and whether the bearings and moving parts are damaged, among other things. 　　Third, keep each part properly, and replace any damaged parts. When disassembling the gear oil pump, it is necessary to take care of every component; special attention should be paid to the flame-proof surfaces of the flame-proof components to ensure they are not damaged or scratched. This includes insulating gaskets and sleeves – if any of these are damaged, they must be replaced with new identical parts. Substitutes with lower performance than the original materials or parts that do not meet the specified specifications must not be used. During assembly, all parts should be placed back in their original positions, without any omissions. 　 Fourth, pay attention to the insulation resistance of gear oil pumps. For electric liquid suction pumps in the single-unit dust collector series that are not used for long periods of time or are operated in humid conditions, it is necessary to measure the insulation resistance of their windings using a 500-volt megohmmeter before use. If the insulation resistance between the windings and the motor casing is less than 7 megohms, measures must be taken to address the windings. 　　Fifth, take care to store electric oil pumps in a dry, clean environment free from corrosive gases. Common causes of failure in gear oil pumps: 1. Wear of internal components of the oil pump. Wear of these internal components can lead to internal leakage. Among them, the large leakage area between the floating bushing and the gear end face is the main cause of internal leakage. This portion of the leakage accounts for about 50% to 70% of the total internal leakage. In a gear pump with internal wear and leakage, its volumetric efficiency decreases, resulting in the pump’s output power being **lower than its input power**. All of its losses are converted into heat energy, which can cause the oil pump to overheat. If the bonding plane is compressed, wear will occur due to the slight movement of the floating bushing during operation, resulting in slow lifting or inability to lift the agricultural tool; such a floating bushing must be replaced or repaired. 2. Wear of the oil pump housing is mainly due to wear in the holes of the floating bushings (the normal clearance between the gear shaft and the bushing is 0.09–0.175 mm, with a maximum of 0.20 mm). The gears operate under the influence of pressurized oil; the tips of the gears are close to the oil pump housing, causing wear on the low-pressure chamber of the pump body. Another type of wear is the circumferential wear on the working surface inside the housing; this wear is mainly caused by impure oil, so it is necessary to use oil free from impurities. 3. Wear of the oil seal, aging of the rubber seal, and deterioration of the rubber oil seal in the unloading plate cause it to lose its elasticity; as a result, it can no longer provide a sealing barrier between the high-pressure oil chamber and the low-pressure oil chamber. This allows the oil pressure in the high-pressure chamber to leak into the low-pressure chamber, a phenomenon known as \"internal leakage\". It reduces the operating pressure and flow rate of the oil pump. In the case of a skeleton-type oil seal, if it is damaged or becomes ineffective over time, air will be drawn into the oil pump through the gaps between the oil seal and the spindle journal, or from the junction between the oil inlet flange and the oil pump housing. This air then enters the oil tank via the return pipe, where it causes numerous bubbles to form. 4. Insufficient oil supply from the oil pump or no oil pressure. Symptoms: The working device lifts slowly, shakes while lifting, or fails to lift at all ； Bubbles in the fuel tank or fuel lines ； The hydraulic system makes a \"hiss, hiss\" sound during lifting ； Cause of failure: (1) Low oil level in the hydraulic oil tank ； (2) Hydraulic oil was not used according to the season ； (3) The oil inlet pipe is severely blocked by debris ； (4) The oil seal of the oil pump’s driving gear is damaged, allowing air to enter the hydraulic system ； (5) The \"O\"-ring seals at the inlet and outlet connections of the oil pump, or those on the elbow fittings, are damaged; the fastening bolts of the elbow fittings or the nuts on the inlet and outlet pipes are not tightened properly, allowing air to enter the hydraulic system ； (6) Internal leakage in the oil pump, aged seal ring ； (7) Wear or scarring on the end face of the oil pump or on the end faces of the shaft sleeves of the driving and driven gears; the unevenness of the end faces of these two shaft sleeves is out of tolerance ； (8) Internal leakage caused by incorrect assembly of internal components of the oil pump ； (9) Installing a “right-handed” oil pump in a “left-handed” setup, resulting in damage to the skeleton oil seal ； (10) The hydraulic oil is too dirty. Exclusion method: (1) Add or replace the oil with a grade that meets the requirements according to the season, up to the specified oil level. Remove any foreign objects from the oil pipe, and tighten the bolts or nuts at the joints ； (2) Replace the aged or damaged frame oil seal or “O”-ring seal ； (3) Replace the worn gear oil pump or oil pump shaft sleeve; if the wear is minor, grind the end face flat on a flat surface. (4) The unloading plate and seal ring must be installed in the oil inlet chamber so that the two shaft sleeves can remain balanced. The unloading plate seal ring should have a pre-pressure of 0.5 mm ； , (5) The elasticity of the guide wire should be sufficient to twist both the upper and lower shaft sleeves by a slight angle in the direction of rotation of the driven gear, so that the machined surfaces of the shaft sleeves of the driving and driven gears fit tightly together ； (6) The unloading groove on the shaft sleeve must be located on the low-pressure side in order to eliminate the harmful dead volume that is generated during gear meshing ； 7) Before pressing in the self-tightening oil seal, apply a layer of lubricant to its surface. Also, make sure that the oil-repellent edge faces the front cover; it must not be installed backwards ； . (8) A “right-handed” pump cannot be installed on a “left-handed” machine, otherwise it will damage the frame oil seal ； (9) Before installing the pump cover, a small amount of engine oil must be poured into the pump casing, and the meshing gears must be turned by hand ； (10) Before tightening the bolts after installing the oil pump cover, check the gap between the pump cover and the pump body to ensure it is within the range of 0.3–0.6 mm. If the gap is too small, replace the sealing ring and pressure relief components. After the hydraulic oil pump is installed, it should rotate smoothly without any sticking. I. Causes of leakage in the mechanical seals of gear pumps and gear oil pumps:
a. Leakage due to the precipitation of solid materials, solidification of the medium, and adhesion.
b. Corrosion, electrochemical corrosion.
c. Excessively high rotational speed or pressure.
d. Excessive vibration, cavitation, surging, and abnormal bearings.
e. Dry friction, negative pressure, cavitation at the seal area, suction, and evacuation. 　　f Thermal shock, rapid cooling/heating
g Excessive temperature difference
h Pressure testing exceeding limits, too high pressure, back pressure

Caused phenomena:
Abnormal leakage

Improvement measures:
Install filtering devices for media containing particles.
For cases where the medium itself cannot be used as a flushing fluid, external flushing methods should be employed.
Check the performance of the pump and seals, and improve the method of use.
Enhance flushing and rapid cooling to improve the operating environment of the seals.

Original post links:
Analysis of leakage causes in gear oil pumps: http://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1004957
Methods for maintaining gear oil pumps: http://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1016495
How to troubleshoot gear oil pump failures: http://bbs.hcbbs.com/forum.php?mod=viewthread&tid=785486
Parts for gear oil pumps and troubleshooting: http://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1012580
Fault analysis and troubleshooting methods for gear oil pumps: http://bbs.hcbbs.com/forum.php?mod=viewthread&tid=131458

Summary: Comprehensive analysis of gear oil pump failures:
I. Severe leakage in the mechanical seal of the gear oil pump:
1. Insufficient spring pressure
1. Readjust the spring compression or replace the spring.
2. Corrosion, wear, or scratches on the end faces of the rotating or stationary ring
2. Repair or replace the damaged rotating or stationary ring.
3. Loose fixing screws, causing the spring to lose its function
3. Tighten the screws or readjust the spring.
4. The sealing ring of the rotating ring is misaligned or corroded/deformed
4. Reinstall or replace the sealing ring for the rotating ring.
5. The stationary ring is misaligned
5. Reinstall the stationary ring.
6. Insufficient precision and surface finish of the shaft sleeve, affecting the axial movement of the rotating ring
6. Replace with a shaft sleeve that meets the required precision standards.
7. Impurities, foreign objects, or medium crystals affecting the axial movement of the rotating ring or interfering between the end faces of the rotating and stationary rings
7. Remove impurities, foreign objects, and crystals; thoroughly clean the sealing elements.

II. Insufficient head of the gear oil pump:
1. Severe corrosion of the impeller of the gear oil pump
1. Replace the impeller with a new one.
2. The performance of the gear oil pump does not meet the design requirements
2. Replace it with a gear oil pump that meets the design requirements.
3. Insufficient rotation speed
3. Check the current and restore the proper rotation speed.
4. Excessive gap between the semi-open impeller and the pump cover
4. Reduce the gap between the impeller and the pump cover.

III. Insufficient flow rate of the gear oil pump:
1. The check valve is too small
1. Replace it with a suitable check valve for the gear oil pump.
2. The suction pipe is not submerged deep enough, allowing air to enter the gear oil pump
2. Increase the depth of submersion of the suction pipe.
3. The suction pipeline is too thin or blocked by debris
3. Replace it with a suitable pipeline and remove any debris.
4. The impeller of the gear oil pump is severely worn or corroded
4. Replace it with a new impeller.
5. The sealing rings of the gear oil pump are severely worn or corroded
5. Replace them with new ones.
6. Excessive gap between the semi-open impeller and the pump cover
6. Reduce the gap between the impeller and the pump cover.
7. The rotation speed of the gear oil pump has decreased too much
7. Check the current and restore the proper rotation speed.

IV. Overheating of the bearings of the gear oil pump:
1. No lubricant (grease) available or insufficient amount
1. Add lubricant (grease) to the required level.
2. The gear oil pump and the motor shaft are not aligned
2. Adjust them so that the axes of the gear oil pump and the motor are aligned.
3. The bearings of the gear oil pump are damaged
3. Replace them with new, healthy bearings.

V. Points to note when installing the packing seal of the gear oil pump:
(1) The outer circular runout of the shaft sleeve of the gear oil pump should not exceed 0.05 mm. 　　(2) After cutting the packing for the gear oil pump, the overlapping edges are set at 45 degrees, and before installation, the packing is pressed and shaped in a special mold according to the dimensions of the shaft. 　　(3) The packing for the gear oil pump is placed in the packing chamber, with each layer of packing overlapping at staggered positions. Before starting the machine, the packing gland must be loosened, and it should be tightened gradually after the machine begins to operate. 　　VI. Assembly of the gear oil pump: (1) Check whether the rubber O-rings of the gear oil pump are damaged or swollen; if so, they must be replaced. 　　(2) Keep the moving and stationary ring surfaces of the gear oil pump absolutely clean and apply a small amount of oil. 　　VII. Disassembly of the gear oil pump: (1) Unscrew the drain plug on the suspension frame to drain all the lubricating oil, then remove the motor. 　　(2) Loosen the connecting bolts between the gear oil pump body and the bearing housing, and separate the impeller, shaft seal, bearing housing from the gear oil pump body. 　　(3) Loosen the impeller nut and remove the impeller and the flat key. 　　(4) Remove the shaft seal assembly and the sealing portion; for mechanical seals, take out the stationary ring, and for packing seals, remove the packing cover to access the packing. 　　(5) Remove the rotating part of the mechanical seal and the shaft sleeve from the shaft; for a packing seal, only the shaft sleeve needs to be removed. 　　(6) Remove the bracket of the bearing housing and the coupling. 　　(7) Remove the bearing cover, water-shedding rubber ring, gear oil pump shaft, and bearings. 　　VIII. Installation sequence of the gear oil pump: (1) When the entire gear oil pump set arrives at the site, the motor has already been installed; it is not necessary to remove the gear oil pump and the motor when leveling the base. 　　(2) The base surface on which the gear oil pump is installed should be leveled. After the cement in the foundation has set, the gear oil pump is installed on this base, and a level is used to check its levelness. If it is not level, shims should be used to adjust it until it is level. Afterwards, concrete is poured into the grouting holes as well as the holes for the anchor bolts. 　　(3) After the cement has dried, check whether the base and foot bolts are loose; once they are in proper position, tighten the nuts of the foot bolts. Finally, check the levelness of the entire unit – if there is any unevenness, use shims to level it out. 　　IX. Preparation work for installing the gear oil pump: (1) Inspect the motor of the gear oil pump to ensure that it has not been damaged during transportation and handling. 　　(2) Inspect the tools and lifting machinery, as well as the foundation of the machines. 　　X. Overheating of the motor used in the gear oil pump:
1. The operating range (flow rate, head) exceeds the design requirements of the gear oil pump.
1. Select an appropriate motor according to the series specifications.
2. The density of the medium is higher than what the motor designed for the gear oil pump can handle.
2. Use a motor suitable for the gear oil pump.
3. Is the packing gland tightened too much, or are the springs of the mechanical seal set too tightly?
3. Adjust the compression of the gland or the springs of the mechanical seal.
4. The gear oil pump has poor assembly quality; there are friction points, or the motor and the pump shaft are not aligned.
4. Check the assembly quality and eliminate any assembly-related issues.

XI. Severe leakage due to the packing seal of the gear oil pump:
1. The packing in the gear oil pump is not tightened enough.
1. Tighten the packing gland to the appropriate degree.
2. The packing mechanism in the gear oil pump is not functioning properly.
2. Adjust the packing so that it is not aligned in the same direction.
3. The packing in the gear oil pump is of uneven size or is severely worn.
3. Replace the packing with one of the same type.
4. The quality of the packing is poor, resulting in poor sealing.
4. Replace it with packing that meets the required standards.
5. The shaft sleeve of the gear oil pump is severely worn.
5. Replace the shaft sleeve.

XII. Severe vibration in the gear oil pump:
1. The shafts of the motor and the pump are not aligned.
1. Align the axes of the pump and the motor.
2. The shaft of the gear oil pump is bent.
2. Remove it, straighten it, or replace it.
3. The impeller of the gear oil pump is unbalanced.
3. Adjust the balance of the impeller.

XIII. Possible faults in the gear oil pump and their solutions:
1. The gear oil pump does not have liquid filled inside it.
1. Refill the pump.
2. The suction pipe, discharge pipe, or internal flow channels of the pump are blocked.
2. Remove any obstructions.
3. Gas is not completely removed from the suction pipe or inside the pump.
3. Inspect the suction pipeline and remove all gas.
4. The suction height of the gear oil pump exceeds the allowed limit.
4. Reinstall the pump according to the allowable suction height.
5. The discharge pipe is too narrow, causing excessive pressure losses.
5. Use a discharge pipe that is suitable.
6. The pump is being used at a head higher than its designed capacity.
6. Select a different pump.
7. The gear oil pump is transporting hot or volatile fluids.
7. Reduce the suction height or install the pump in reverse orientation.
8. The rotation direction of the gear oil pump is incorrect.
8. Correct the rotation direction