Analysis of Common Faults and Solutions for Rexroth Relief Valves
During the use of the Rexroth relief valve, common issues include noise, vibration, radial jamming of the valve core, and pressure regulation failures. These problems can significantly affect system performance and operational reliability. (1) Noise and Vibration: The primary sources of noise and vibration in hydraulic systems are often pumps and valves, particularly relief valves and directional control valves. The noise from relief valves typically includes flow-induced sounds and mechanical noises. Flow-induced sounds are primarily caused by oil vibration, cavitation, and hydraulic shocks. Mechanical noise stems from the impact and friction between components within the valve. One significant cause of noise is uneven pressure distribution. For example, in Rexroth pilot-operated relief valves, the pilot valve section is highly prone to vibration. When operating under high-pressure conditions, the axial opening of the pilot valve is minimal, around 0.003 to 0.006 cm, resulting in a small flow area and extremely high velocity, up to 200 m/s. This high-speed flow often leads to uneven pressure distribution, causing an imbalance in the radial forces on the conical valve, which triggers vibrations. Additionally, manufacturing defects such as ovality in the conical valve or its seat, contamination in the pilot valve port, or deformation of the pressure-regulating spring can exacerbate the vibration. As a result, the pilot valve is often identified as the source of the problem. The presence of elastic components like springs and moving masses creates conditions conducive to oscillations. The front chamber of the pilot valve acts as a resonant cavity, amplifying the vibration of the poppet valve and leading to overall valve resonance and noise. When noise occurs, it is frequently accompanied by severe pressure fluctuations. Cavitation noise arises when air enters the hydraulic fluid or when the oil pressure drops below atmospheric levels. This results in the formation of bubbles in the low-pressure zones. When these bubbles move to high-pressure areas, they collapse, causing rapid changes in volume and generating noise. This instantaneous process also induces localized hydraulic shocks and vibrations. In pilot-operated relief valves, the flow rates and pressures differ significantly between the pilot valve and the main valve port, making cavitation more likely and contributing to noise and vibration. Hydraulic shock noise occurs when the Rexroth pilot-operated relief valve is unloaded. This happens due to the sudden drop in circuit pressure, creating pressure shock waves. Higher system pressures and larger working conditions amplify the intensity of the impact noise. The brief relief time of the relief valve causes hydraulic shock, and the sudden change in oil flow rate generates pressure wave impacts. Although individual pressure waves produce minimal noise, they can resonate with mechanical components in the system, intensifying vibrations and noise. Consequently, when hydraulic shock noise occurs, it is usually accompanied by noticeable system vibrations. Mechanical noise originates from impacts and friction between components, often due to machining errors. Pilot-operated relief valves may emit high-frequency self-excited vibration sounds, known as mechanical vibrations. These sounds depend on factors like return line configuration, flow rate, pressure, oil temperature (viscosity), and others. Smaller pipe diameters, lower flow rates, higher pressures, and lower oil viscosities tend to increase the likelihood of self-excited vibration. To mitigate noise and vibration, vibration-damping elements can be added to the pilot valve section. These elements, such as damping sleeves, are fixed in the resonant cavity (the front chamber of the pilot valve) and prevent free movement. Damping holes on the sleeve increase resistance, reducing vibration. Adding components to the resonant cavity decreases its volume and increases the oil's stiffness, reducing resonance potential. Anti-vibration pads, which cooperate with the resonant cavity, have throttle grooves on both sides, creating a damping effect when oil flows through them. These pads disturb the original resonance frequency and reduce the possibility of resonance by altering the flow conditions. Gas-suppressing plugs with air storage holes and throttling edges trap air in the hole, which compresses and absorbs vibrations when pressed, acting as a micro-vibrator. The compressed air fills the oil when compressed and discharges it hydraulically when expanded, introducing additional flow changes that help reduce noise and vibration. Improper assembly or use of the relief valve, such as misalignment of concentric sections or excessive wear of the conical valve, can also lead to vibration and noise. In such cases, careful inspection or replacement of parts is necessary. (2) Radial Jamming of the Valve Core: Radial jamming occurs due to machining inaccuracies, causing the main valve core to become stuck, preventing the valve from opening or closing properly under pressure. Contamination is another common cause of radial jamming. (3) Pressure Regulation Failure: Rexroth relief valves may experience pressure regulation failures. Two typical scenarios involve the pilot-type relief valve: either the pressure does not reach the set value when adjusting the pressure regulator, or the pressure does not decrease after adjustment, instead rising continuously. Besides radial jamming, other causes include blockage of the main valve body damper, which prevents oil pressure from reaching the upper chamber of the main valve and the front chamber of the pilot valve, rendering the pilot valve ineffective in regulating the main valve pressure. If the pressure-regulating spring is deformed or improperly selected, or if the spring has insufficient compression travel, excessive internal leakage, or severe wear of the pilot valve spool, the pressure will not reach the rated value. Another issue is blockage of the damper, which prevents oil pressure from reaching the conical valve, disabling the pilot valve’s ability to regulate the main valve pressure. When the damper is blocked, the conical valve cannot open under any pressure, halting oil flow and keeping the pressures in the upper and lower chambers of the main valve equal. Since the annular pressure area at the top of the main valve core is larger than at the bottom, the valve remains closed, preventing overflow. As the load increases, the main valve pressure rises accordingly. If the actuator stops working, the system pressure will rise uncontrollably. Additional checks should be conducted for external control port blockages and proper installation of the conical valve. (4) Other Faults: External leakage may occur due to damaged O-rings, combination seals, or loose mounting screws and pipe joints during assembly or use. Excessive wear of the conical valve or poor sealing surfaces can lead to excessive internal leakage, affecting normal operation. Electromagnetic relief valves may experience issues such as failure of the先导valve, failure of the main valve, and impact noise during unloading. Adjusting or adding a buffer can help reduce or eliminate this noise. Alternatively, a backpressure valve can be added to the main valve overflow, typically adjusted to around 5 kgf/cm² (0.5 MPa). In conclusion, understanding the root causes of these common faults is crucial for effective maintenance and optimization of Rexroth relief valves, ensuring smooth system operations and minimizing downtime.60V Battery Pack ,Battery Pack With Outlet,Back Up Battery Pack,Ev Battery Pack
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