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During the operation of the pressure reducing valve, it was found that the oil inside the pressure regulating chamber of the pressure reducing valve was extravasated at the joint between the connecting sleeve and the valve body; during the process of disassembling the pressure reducing valve, the connection of the connecting sleeve was found. The solidified fastening glue on the thread forms a concave-convex surface, and the O-ring has been deformed to form a leakage passage, which seriously affects the sealing between the connecting sleeve and the valve body.
1. Analysis of the sealing problem After analysis with the relevant experts, it is found that the seal between the connecting sleeve of the pressure reducing valve and the valve body mainly relies on the O-ring between the connecting sleeve and the inner wall of the valve for circumferential sealing. Once the seal is effective, its external leakage is inevitable. After checking and analyzing the disassembly of the leaking part, it is considered that the seal between the connecting sleeve and the valve body has the following problems.
(1) The sealing surface of the valve body is not sealed. Since the connecting sleeve of the pressure reducing valve and the valve body mainly rely on the thread connection; in order to prevent the thread from loosening, when the pressure reducing valve is assembled, the fastening glue is applied on the external thread of the connecting sleeve, and the fastening glue overflows to the O-ring. On the ring sealing surface, the fastening rubber forms a rough surface on the sealing surface after solidification, forming a leakage passage, which makes the O-ring inner and outer seals not tight, leaving a hidden danger for oil leakage.
(2) The O-ring compression is low, causing the O-ring seal to fail. At present, the specification of the O-ring between the connecting sleeve and the valve body is φ31.47mm×φ1.78mm, the depth of the sealing groove is 1.6mm, and the compression ratio of the O-ring is 10.1%, which is much lower than the normal theoretical static sealing compression ratio. 15% to 30%, the sealing surface cannot be effectively sealed, resulting in seal failure.
(3) Defects in the form of the seal itself. The seal between the pressure reducing valve connecting sleeve and the valve body is completely sealed in the circumferential direction by the circumferential compression of the O-ring. Although the sealing form is widely used, the assembly operation is strict. In the assembly, the O-ring and the circumferential sealing surface are required to be in a vertical state. Otherwise, the O-ring is easily deformed into an elliptical shape in the circumferential direction, which causes the O-ring and the sealing surface to be ineffective contact, and the Zui final seal fails. After inspection of the O-ring, it was found that the outer circumference of the O-ring was scratched to form an oil extravasation passage.
(4) The friction between the O-ring and the sealing surface is too large. Since the O-ring rotates along with the sealing surface during the installation process, since the hardness of the O-ring is relatively small with respect to the sealing surface, scratches are easily generated, thereby causing leakage.
The above four problems in the seal between the connecting sleeve and the valve body are important factors affecting the oil leakage between the connecting sleeve of the pressure reducing valve and the valve body, and therefore the measures for solving the problem should also surround these four problems.
2. Measures to solve the sealing problem In response to the above analysis of the oil leakage of the pressure reducing valve, measures to solve the problem are proposed from four aspects.
(1) Improve the quality of the sealing surface. Remove the fastening rubber on the sealing sleeve and the sealing surface of the valve body, check the surface roughness, review the sealing surface size, and improve the sealing effect of the O-ring and sealing surface.
(2) Guarantee the compression of the O-ring. The size of the O-ring between the connecting sleeve and the valve body is changed from φ31.47 mm×φ1.78 mm to φ31 mm×φ2 mm, so that the compression amount of the O-ring is increased from 10.1% to 20%, thereby improving the O-ring. The area of ​​the sealing surface.
(3) Increase the face seal. Although the above measures are taken to improve the quality of the sealing surface and increase the compression of the O-ring, the leakage of the oil can be prevented to a certain extent; however, the hidden trouble of the O-ring leakage cannot be fundamentally solved; therefore, in the above measures On the basis of this, the end face seal is further increased in the axial direction of the connecting sleeve and the valve body, the depth of the mounting groove is 1.5 mm, the specification of the O-ring is φ24.5 mm×φ2 mmmm, and the compression amount is 25%. The advantage of the end face seal is that the O-ring is in full contact with the sealing surface, which improves the sealing effect.
(4) Reduce the friction between the O-ring and the sealing surface. When assembling the connecting sleeve and the valve body, apply a clean lubricating oil to the O-ring and sealing surface to reduce the frictional resistance and prevent the O-ring from being scratched.
3. Sealing effect after transformation (1) The quality of the sealing surface of the connecting sleeve and the valve body is improved to ensure the sealing quality of the O-ring.
(2) The amount of compression of the O-ring is improved, and the sealing effect is further improved.
(3) Increasing the face seal, fundamentally solves the problem of leakage of the pressure reducing valve.
(4) The friction between the O-ring and the sealing surface during assembly is reduced, and the occurrence of scratches is avoided.
Failure Analysis of Static Seal of Pressure Reducing Valve
As an important component in the hydraulic system, the function of the pressure reducing valve is to make the outlet pressure lower than the inlet pressure and keep the outlet pressure stable, independent of the inlet pressure and flow rate; once the leakage occurs, it not only affects the normal production, but also causes the hydraulic pressure. The loss of oil, polluting the environment; in the marine hydraulic system, the pressure reducing valve as the main control element, the importance of its sealing is self-evident.