Hydraulic valve failure analysis and maintenance

With the prolonged use of the hydraulic valve, failure or failure is inevitable. The failure or failure of the hydraulic valve is mainly caused by excessive clearance caused by factors such as wear and cavitation, leakage of the hydraulic valve, and malfunction or clamping of the hydraulic valve spool caused by deposition of hydraulic oil contaminants. When the hydraulic valve fails or fails, most companies use the replacement of new components to restore the hydraulic system function, and the failed hydraulic valve becomes a waste product. In fact, most of these hydraulic valves are still in good condition and can be restored after partial maintenance. Studying the meaning of hydraulic valve repair is not only to save the cost of component purchase. When the failed hydraulic valve has no spare parts or the order takes a long time, and the equipment may be shut down for a long time, the maintenance can temporarily maintain the economic benefits of the operation of the equipment and the entire production line. It is quite impressive. In the practice of hydraulic valve maintenance, the commonly used repair processes include hydraulic valve cleaning, component combination matching, repair size, etc., which are described below.

1 hydraulic valve cleaning

Disassembly cleaning is a process of maintenance of hydraulic valves. For hydraulic valve failure caused by oil contamination due to hydraulic oil contamination or particulate impurities in hydraulic oil, it is generally possible to remove the fault and restore the function of the hydraulic valve.

Common cleaning processes include:

(1) Disassembly. Although the parts of the hydraulic valve are mostly bolted, the hydraulic valve design is non-disassembled. If there is no special equipment or professional technology, forcible disassembly may cause damage to the hydraulic valve. Therefore, it is necessary to grasp the structure of the hydraulic valve and the connection method between the parts before disassembly, and record the positional relationship between the parts when disassembling.

(2) Check and clean up. Check the dirt deposits of parts such as valve body and valve core, and remove the concentrated dirt with cotton yarn, brush and non-metal scraper without damaging the working surface.

(3) Rough washing. The valve body, the valve core and other parts are placed on the tray of the cleaning box, heated and immersed, and the compressed air is passed into the bottom of the cleaning tank, and the residual dirt is washed away by the agitation action of the air bubbles, and the ultrasonic cleaning can be used conditionally.

(4) Fine washing. Use a high-pressure cleaning solution to clean the solution, and then dry it with hot air. Conditional companies can use existing cleaning agents, and organic cleaning agents such as diesel and gasoline can also be used in individual applications.

(5) Assembly. According to the hydraulic valve assembly diagram or the assembly of parts recorded during disassembly, be careful when assembling, do not touch the parts. The original sealing material is easily damaged during disassembly and should be replaced during assembly.

Pay attention to the following issues when cleaning:

(1) For long deposition time, stick a firm dirt, and do not scratch the mating surface when cleaning.

(2) Pay attention to safety when heating. Some inorganic cleaning solutions are toxic. Heating and volatilizing can cause human poisoning and should be used with caution; organic cleaning liquids are flammable and should be fireproof.

(3) When selecting the cleaning solution, pay attention to its corrosiveness and avoid corrosion of the valve body.

(4) After cleaning, the parts should be preserved to avoid rust or re-contamination.

(5) The assembled hydraulic valve can be put into use after passing the test.

2 parts combination matching maintenance method

In the manufacturing process of hydraulic valve, in order to improve the assembly precision, the matching method is adopted. That is, for a batch of processed parts, such as the valve body and the valve core, according to the actual size, the matching gap Zui is selected as an appropriate pair to ensure good. Spool sliding and sealing performance. That is to say, the same type of hydraulic valve, the valve core and the valve body have different dimensions. For the enterprise, when a certain number of failed hydraulic valves are large, all the valves can be disassembled and cleaned, and the parts are inspected and tested. According to the test results, the parts are classified and re-assembled according to the following methods.

After inspection, if the valve core and valve body are evenly worn, and the working surface is not seriously scratched or partially severely worn, select the valve core with proper clearance and reassemble the valve body according to the relevant manual; if the valve core and valve body are not worn, Uniform or scratched work surface. If the hydraulic valve function cannot be restored by the above method, select a pair of valve cores and valve bodies that meet the interference requirement of the machining allowance (the valve body with small hole size and large outer diameter) Spool), reaming or grinding the valve body hole, grinding the valve core to achieve reasonable shape accuracy and precision assembly. The shape accuracy and matching clearance of common hydraulic valve hole are shown in Table 1.

3 Recovery size maintenance method

The use of the parts selection method to repair the hydraulic valve is simple, but has its limitations, and the repair size method is suitable for a wider range of applications. The simple and feasible repair size method mainly includes two types of replacement parts method and repair method.

The replacement part method is to disassemble the valve core that has lost the matching precision, measure and draw the part drawing; check the degree of wear or damage of the valve body guiding hole or the valve seat, and determine the repair processing amount according to this, and then perform finishing (fine reaming) Or grinding) repair. For a valve seat with a certain taper, a specific machining tool is to be made. After machining to the appropriate accuracy, measure the actual size and then machine the new spool according to this size. This maintenance method has high maintenance precision, wide adaptability, and can fully restore the original accuracy, and is suitable for enterprises with certain processing capabilities.

There are many kinds of repair and repair processes, and the common process method suitable for hydraulic valve repair is brush plating or electric coating. The reasonable repair thickness of electro-coating is less than 012mm, which basically meets the maintenance requirements of uniform wear hydraulic valve, and still needs subsequent processing after repair. The commonly used electrocoating process is chemical composite electrocoating. The chemical composite electrocoating is developed on the basis of mature electroplating process. It has the advantages of simple equipment, convenient operation, low cost, easy reaction control, etc. The process can be in the valve. A composite coating with various components is deposited on the surface of the core or valve hole. The coating is firmly bonded to the parent metal and has high mechanical strength, excellent thermal conductivity, low coefficient of thermal expansion, low coefficient of friction and strong self. Repair ability. The formulation and process conditions of typical chemical composite plating solutions are shown in Table 2.

4 Summary

The carefully repaired hydraulic valve not only restores its original function, but its life, work performance and reliability can be close to the original level. The use of new technology and new materials in maintenance can also prolong its life and improve work performance. Due to the different maintenance techniques and equipment levels of different companies, the quality of maintenance will vary greatly. For companies with inadequate maintenance equipment and technology, even if the hydraulic system is restored to its original state after maintenance, monitoring should be strengthened and spare parts should be actively purchased to cope with unexpected failures.