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Cause Analysis and Elimination of Common Faults of Overflow Valve
(A) of the noise and vibration Hydraulic equipment prone to noise components generally considered to be pumps and valves, the valve again with relief valve and solenoid valve-based. The noise generated by many factors. The noise of the relief valve has two kinds of velocity sound and mechanical sound. Velocity of sound mainly by the oil vibration, cavitation and hydraulic shock and other causes of noise. Mechanical noise is mainly caused by the impact of the valve parts and friction and other causes of noise. (1) Noise caused by uneven pressure The pilot valve part of the pilot-operated relief valve is an easily vibrated part as shown in Fig.3. In the case of overflow under high pressure, the pilot valve axial opening is small, only 0.003 to 0.006 cm. Flow area is very small, high velocity, up to 200 m / s, easily lead to uneven pressure distribution, the unbalanced radial force cone valve vibration. In addition cone valve and cone valve seat generated during processing ovality, valve port dirt stuck and pressure regulating spring deformation, etc., can also cause cone valve vibration. Therefore, it is generally believed that the pilot valve is the noise generating vibration source. Due to the presence of the elastic element (spring) and the mass of the movement (cone valve), an oscillating condition is created and the pilot valve cavity acts as a resonant cavity, so that the cone valve vibrates easily causing the entire valve Resonance and make noise, when the noise occurs more often accompanied by intense pressure beating. (2) Cavitation noise When air is drawn into the fluid for various reasons or when the fluid pressure is lower than the atmospheric pressure, part of the air dissolved in the fluid is precipitated to form bubbles that are trapped in the low-pressure zone When the volume is large, when the oil flows to the high pressure zone, it is compressed, the volume suddenly becomes smaller or the bubble disappears. On the contrary, if the volume is small when in the high pressure zone, when the flow goes to the low pressure zone, the volume suddenly increases , The bubble of oil in this rapidly changing phenomenon. Sudden changes in the bubble volume will produce noise, but also because this process occurs in an instant, will cause local hydraulic shock and vibration. Pilot-type relief valve pilot valve port and the main valve port, fluid flow and pressure changes greatly, it is prone to hole phenomenon, resulting in noise and vibration. (3) Noise generated by hydraulic impact When the pilot-operated relief valve is unloaded, pressure shock noise may occur due to a sudden drop in pressure in the hydraulic circuit. The more high-pressure high-capacity working conditions, the greater the impact noise, which is due to the relief valve relief time is very short and the resulting hydraulic shock at the time of unloading, due to drastic changes in oil flow rate, causing sudden pressure changes, resulting in Pressure wave impact. The pressure wave is a small shock wave and produces very little noise itself, but as the oil reaches the system, vibrations and noise can be amplified if it resonates with any mechanical part. So in the event of hydraulic impact noise, usually accompanied by system vibration. (4) mechanical noise Pilot-type relief valve issued by the mechanical noise, usually from the impact of parts and due to processing errors arising from friction parts. In the pilot relief valve noise, sometimes there is a mechanical vibration of high-frequency vibration, commonly known as self-excited vibration sound. This is the main valve and pilot valve sound due to high-frequency vibration. Its incidence and return pipe configuration, flow, pressure, oil temperature (viscosity) and other factors. Under normal circumstances, the pipe diameter is small, less flow, high pressure, low viscosity oil, self-excited vibration on the high rate. To reduce or eliminate the pilot-type relief valve noise and vibration measures, usually in the pilot part of the anti-vibration components added. Anti-vibration sleeve generally fixed in the pilot valve cavity, the resonator, can not be free. In the damping sleeve are equipped with a variety of damping holes to increase the damping to eliminate vibration. In addition, due to the addition of components in the resonator, the volume of the resonator is reduced, and the stiffness of the fluid under negative pressure is increased. According to the principle that the stiff components are not easily resonated, the possibility of resonance can be reduced. Resonance pad generally with the resonant cavity activity coordination, freedom of movement. Vibration pad front and back have a throttling tank, oil flow can produce damping effect, in order to change the original flow. Due to the addition of anti-vibration pad, an additional vibration element, upset the original resonant frequency. Resonator increases the damping pad, also reduces the volume, increasing the stiffness of the oil pressure to reduce the possibility of resonance. In the anti-vibration plug is provided with gas storage holes and throttling edge, due to retain the air holes in the air, compressed air compression, compressed air has a vibration-absorbing effect, the equivalent of a miniature vibration absorber. Small holes in the air compression, filling the oil, expansion, the oil pressure, thus adding an additional flow, in order to change the original flow. It can also reduce or eliminate noise and vibration. In addition, if the overflow valve assembly or use of their right to improper use, but also cause vibration, resulting in noise. Such as the three concentric relief valve, the assembly of three concentric with the improper use of traffic flow is too large or too small, the cone valve is not normal wear and tear. In this case, you should carefully check the adjustment, or replacement parts. (B) the radial tightness of the spool due to the impact of processing accuracy, resulting in the main spool radial clamping, the main valve is not open on the pressure or the main valve is closed without pressure relief, and the other due to pollution caused by radial clamping. (C) pressure regulator failure relief valve in use sometimes appear pressure regulator failure. Pilot-type pressure relief valve failure relief there are two situations: one is to adjust the pressure hand wheel can not afford to build pressure, or the pressure does not reach the rated value; the other hand pressure adjustment does not decline, and even continue to step up pressure. Pressure regulator failure, in addition to the spool for a variety of reasons caused by radial clamping, there are some of the following reasons: First, the main valve body (2) blockage of the damper, hydraulic transmission less than the main valve and the pilot valve on the front Cavity, pilot valve on the main valve to lose the role of pressure regulation. Due to the oil pressure in the main valve cavity, the spring force is very small, so the main valve into a spring force is very small direct acting relief valve, the inlet valve cavity pressure is very low, the main valve to open overflow Flow, the system can not afford to build pressure. The reason that the pressure can not reach the rated value is the deformation or selection error of the pressure regulating spring, the insufficient compression stroke of the pressure regulating spring, the excessive internal leakage of the valve, or excessive wear of the pilot valve cone valve. The second is the damper (3) blockage, the hydraulic pressure less than the cone valve, the pilot valve on the main valve to lose the pressure regulation. After the damper (small hole) is clogged, the poppet valve will not open the overflow oil under any pressure, and there is always no flow of oil in the valve. The pressure in the upper and lower cavity of the main valve will always be equal. Since the upper annular pressure area of ​​the main valve plug is larger than The lower annular pressure area, so the main valve is always closed, will not overflow, the main valve pressure increases with the load increases. When the executing agency to stop working, the system pressure will rise indefinitely. In addition to these reasons, the need to check the external control port is blocked, the cone valve installed and so on. (D) other fault relief valve in the assembly or use, due to the O-ring, combination ring damage, or mounting screws, pipe joints loose, may cause undue external leakage. If the cone valve or the main valve core wear is too large, or poor contact sealing surface, it will cause excessive internal leakage, and even affect the normal work. Common failures of electromagnetic relief valve pilot solenoid valve malfunction, failure of the main valve pressure relief and unloading impact noise. The latter can be reduced or eliminated by adjusting the added buffer. If not with a buffer, you can add a back pressure valve in the main valve overflow port. (Pressure is generally adjusted to 5kgf / cm2 or so, that is, 0.5MPa).