Created on:2022-04-06 09:11

Fault analysis and troubleshooting of filter

Fault analysis and troubleshooting of filter

The faults caused by the filter include the faults caused by the poor filtering effect to the hydraulic system, such as the faults caused by the poor filtering and the dirt entering the system.

1. The filter element is damaged and deformed

This fault phenomenon is manifested in the deformation, bending, depression, flattening and breaking of the filter element. The causes are as follows.

(1) The filter element is seriously blocked by pollutants during operation and has not been cleaned in time. The pressure difference between the inflow and outflow of the filter element increases, resulting in insufficient strength of the filter element and deformation and damage of the filter element.

(2) The filter is improperly selected and exceeds its allowable maximum working pressure. For example, as for paper filter, the rated pressure of zu-100x202 is 6.3MPa, while the rated pressure of zu-h100x202 can reach 32Mpa. If the former is used in the hydraulic system with a pressure of 20MPa, the filter element must be broken down and damaged.

(3) In the hydraulic system equipped with high-pressure accumulator, the oil in the accumulator is backfilled and the filter is damaged due to some fault.

Troubleshooting: check and clean the filter regularly in time; The filter shall be selected correctly, and the strength and pressure resistance shall be consistent with the type and model of the filter used; Take corresponding countermeasures for various special reasons.

2. Filter desoldering

This fault is for the metal mesh filter. When the ambient temperature is high or the local oil temperature at the filter is too high, which exceeds or approaches the melting point temperature of solder, plus the original welding is not firm and the impact of oil, it will cause desoldering. For example, the mesh filter at the inlet of the high-pressure piston pump has repeatedly found that the metal mesh is separated from the skeleton, and the local oil temperature at the inlet of the piston pump is as high as 100 ℃. At this time, the solder of the metal mesh can be changed from tin lead solder (melting point 183 ℃) to silver solder or silver cadmium solder, and their melting point is greatly improved (235 ~ 300 ℃).

3. Filter particle dropping

Most of them occur in metal powder sintered filters. After the falling particles enter the system, the orifice is blocked and the stuffy core is stuck. The reason is the poor quality of sintered powder filter element. Therefore, the sintered filter that passes the inspection shall be selected.

4. The filter is blocked

Generally, during the working process of the filter, the surface of the filter element will gradually contain scale, causing blockage is a normal phenomenon. The blockage mentioned here refers to the serious blockage that leads to the failure of the hydraulic system. After the filter is blocked, it will at least cause poor oil absorption of the pump, noise generated by the pump, failure of the system to absorb enough oil, resulting in pressure failure, a large number of bubbles in the oil and possible breakdown of the filter element due to pressure increase due to blockage. After the filter is blocked, it shall be cleaned in time. The cleaning methods are as follows.

(1) Wash with solvent. Common solvents include ethylene trichloride, paint thinner, toluene, gasoline, carbon tetrachloride, etc. these solvents are easy to catch fire and have certain toxicity. Full attention should be paid to cleaning. Alkaline solutions such as caustic soda and caustic potassium can also be used for degreasing cleaning, interfacial active agent degreasing cleaning and electrolytic degreasing cleaning. Although the latter has strong cleaning ability, it is corrosive to the filter element and must be used with caution. After washing, the solvent must be removed as soon as possible by water washing.

(2) Clean by mechanical and physical methods.

1) Clean with a brush. A soft brush shall be used to remove the dirt of the filter element. An excellent steel wire brush will damage the mesh type and wire gap type filter elements and brush off the sintered particles of the sintered filter element. This method is not applicable to paper filter, which is generally combined with solvent cleaning, as shown in Figure 28.

2) Ultrasonic cleaning. The dirt on the filter element can be removed by the action of ultrasonic wave in the cleaning solution, but the filter element is a porous material and has the property of absorbing ultrasonic wave, which may affect the cleaning effect.

3) Heating volatilization method. The crud on some filters can be removed by heating, but it should be noted that carbon ash and solid attachments cannot remain in the filter element during heating.

4) Compressed air blowing. Use compressed air to blow out the scale on the opposite side of the filter deposit layer, and the effect of pulsating air flow is better.

5) Clean with water pressure. The method is the same as above, and the effect is better if the two methods are used alternately.

(3) Acid treatment. When this method is adopted, the filter element shall be sintered metal with the same metal. For copper metals (bronze), remove the dirt on the surface with brilliant dipping solution (h2s04 43.5%, HNO3 37.2%, HCI 0.2%, and the rest is water) at room temperature; Or use the solution made of 20% h2s04 and 30% HNO3 water, remove the dirt and put it in the solution made of cr3o · h2s04 and water to form a corrosion-resistant film.

For stainless steel metals, remove the dirt on the surface with the solution prepared by adding 25% HNO3 and 1% HCI water, then immerse in concentrated HNO3 to remove the free iron, and form a corrosion-resistant film on the surface at the same time.

(4)       Cleaning steps and replacement of various filter elements.

1) Paper filter element. Replace the filter element with a new one according to the filter impedance indicated by the pressure gauge or blockage indicator. Generally, it is not cleaned.

2) Mesh and wire gap filter elements. The cleaning steps are solvent degreasing → brush cleaning → water pressure cleaning → air pressure blowing → drying → assembly.

3) Sintered metal filter element. It can be cleaned with a brush first, and then degreased with solvent (or heated volatilization method, below 400 ℃) → water pressure and air pressure purging (reverse pressure 0.4 ~ 0.5MPa) → acid treatment → water pressure and air pressure purging → air pressure purging and dehydration → thousand drying.

The disassembled and cleaned filter shall be assembled in a clean environment according to the disassembly sequence. If the filter element needs to be replaced, it shall be replaced according to the specifications, including the same appearance and material, the same filtering accuracy and pressure resistance, etc. The seals used in the filter shall be replaced according to the material specifications, and attention shall be paid to the assembly quality, otherwise there will be leakage, loss of oil absorption and drainage, air absorption and other faults.

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