Rexroth Relief Valve - Common Faults and Solutions for Relief Valves

1. Causes of noise and vibration failure of relief valves

The components that are prone to noise in hydraulic devices are generally considered to be pumps and valves, and the valves are mainly relief valves and electromagnetic reversing valves. There are many factors that contribute to noise. There are two types of noise in the relief valve: velocity sound and mechanical sound. The noise in the flow velocity sound is mainly caused by oil vibration, cavitation, and hydraulic shock. The mechanical sound is mainly caused by the impact and friction of the parts in the valve.

(1) Noise caused by uneven pressure

The pilot part of the pilot operated relief valve is a vibration-prone part. In the case of overflow under high pressure, the axial port of the pilot valve is very small, only 0.003-0.006 cm. The overflow area is very small, and the flow rate is very high, up to 200 m/s, which is easy to cause uneven pressure distribution, so that the radial force of the poppet valve is unbalanced and vibrates.

In addition, the ovality of the poppet valve and the poppet seat during processing, the adhesion of dirt to the pilot valve port and the deformation of the pressure regulating spring will also cause the vibration of the poppet valve.

Therefore, the pilot valve is generally considered to be the source of noise. Due to the existence of elastic elements (springs) and moving masses (poppet valves), which constitute a condition for generating oscillation, and the front cavity of the pilot valve plays the role of a resonance cavity, so the poppet valve is easy to cause the resonance of the whole valve and emit noise after vibration, and the noise is generally accompanied by violent pressure beating.

(2) Noise generated by holes

When the air is sucked into the oil for various reasons, or when the oil pressure is lower than the atmospheric pressure, part of the air dissolved in the oil will precipitate to form bubbles, which are larger in the low pressure area, and when they flow with the oil to the high pressure area, they are compressed, and the volume suddenly becomes smaller or the bubbles disappear; On the contrary, if the volume is small in the high-pressure area, and when it flows to the low-pressure area, the volume suddenly increases, and the volume of bubbles in the oil changes rapidly.

Sudden changes in the volume of bubbles produce noise, and because this process occurs instantaneously, it will cause local hydraulic shocks and vibrations. The pilot valve port and the main valve port of the pilot type relief valve have large changes in oil flow rate and pressure, and it is easy to appear cavitation, resulting in noise and vibration.

(3) Noise generated by hydraulic shock

When the pilot operated relief valve is discharged, the pressure rush noise will occur due to the sudden drop in pressure in the hydraulic circuit. The more high-pressure and large-capacity working conditions, the greater the impact noise, which is caused by the hydraulic impact caused by the short unloading time of the relief valve.

The pressure wave is a small shock wave, which produces very little noise by itself, but if it resonates with any mechanical part with the oil into the system, it may increase the vibration and enhance the noise. Therefore, when hydraulic impact noise occurs, it is generally accompanied by system vibration.

(4) Mechanical noise

The mechanical noise emitted by pilot-operated relief valves is generally caused by the impact of parts and the friction of parts due to machining errors, etc. In the noise emitted by the pilot-operated relief valve, there is sometimes a mechanical high-frequency vibration sound, which is generally called self-excited vibration sound. This is the sound that occurs when the main valve and pilot valve are vibrated at high frequency.

Measures to reduce or eliminate noise and vibration

Its incidence is related to factors such as the configuration of the return pipeline, flow rate, pressure, oil temperature (viscosity), etc. Under normal circumstances, the incidence of self-excited vibration is high due to the small diameter of the pipeline, the small flow rate, the high pressure, and the low viscosity of the oil. Measures to reduce or eliminate the noise and vibration of the pilot operated relief valve are generally to add a vibration damping element to the pilot valve part.

The vibration cancelling sleeve is generally fixed in the front cavity of the pilot valve, that is, in the resonance cavity, and cannot move freely. Various damping holes are provided on the vibration cancelling sleeve to increase the damping to eliminate the vibration. In addition, the volume of the resonance chamber is reduced due to the addition of parts to the resonance chamber, and the stiffness of the oil increases under negative pressure, reducing the possibility of resonance by the principle that components with high stiffness are not prone to resonance.

The vibration canceling pad is generally coordinated with the activity of the resonance cavity and can move freely. There is a throttle groove on the front and back of the vibration canceling pad, which can produce a damping effect when the oil flows, so as to change the original flow situation. Due to the addition of vibration cancelling pads, a vibrating element was added, which disturbed the original resonant frequency. The resonance chamber adds vibration cancelling pads, which also reduce the volume and increase the stiffness of the oil when pressurized to reduce the likelihood of resonance.

The anti-vibration screw plug is provided with an air storage hole and a throttle edge, and because there is air left in the gas storage hole, the air is compressed when it is pressurized, and the compressed air has a vibration-absorbing effect, which is equivalent to a miniature vibration absorber. When the air in the small hole is compressed, the oil is filled, and when it expands, the oil is hydraulically discharged, so that an additional flow is added to change the original flow situation. As a result, noise and vibration can also be reduced or eliminated.

In addition, if the relief valve itself is not properly assembled or used, it will also cause vibration and noise. For example, the three-section concentric relief valve is not properly matched during assembly, the flow rate is too large or too small when used, and the abnormal wear and tear of the poppet valve. In this case, adjustments should be carefully checked, or parts should be replaced.

Rexroth Relief Valve - Common Faults and Solutions for Relief Valves

Rexroth Relief Valve - Common Faults and Solutions for Relief Valves

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