Hydraulic noise analysis:
1. Hydraulic pump or motor noise
(1) Absorption is one of the major causes of excessive noise in hydraulic pumps. When the oil is mixed with air, cavitation is easily formed in the high pressure area and propagates in the form of pressure waves, causing the oil to oscillate and cause the system to generate cavitation noise.
The main reasons are:
1. If the oil filter or inlet pipe of the hydraulic pump is clogged or the viscosity of the oil is too high, the degree of vacuum at the pump inlet may be too high to allow air to infiltrate.
2. Damage to the oil seal on the shaft end of the hydraulic pump or pilot pump, or poor seal of the oil inlet pipe, causing air to enter.
3. The oil level of the fuel tank is too low, so that the hydraulic pump inlet pipe is directly evacuated.
When there is a high noise in the work of the hydraulic pump, the above-mentioned parts should be checked first, and the problems found should be handled in time.
(2) Excessive wear of the internal components of the hydraulic pump, such as wear and strain on the cylinder block of the hydraulic pump and the valve plate, rotor and blade fittings, causes serious leakage in the hydraulic pump. When the hydraulic pump outputs high pressure and low flow oil, Generate traffic pulsation and cause higher noise. At this time, the declination of the pilot system variable mechanism can be appropriately increased to improve the influence of internal leakage on the pump output flow.
Hydraulic pump control flow of the piston will also be due to local wear and tear, so that the piston pulsates during the movement, resulting in fluctuations in the output flow and pressure of the hydraulic pump, resulting in greater vibration and noise at the pump outlet. At this point, components that are worn or severely damaged may be brush plated or replaced.
(3) The hydraulic pump distribution plate is also one of the important components that easily cause noise. The use of flow disk in use due to surface wear or sludge deposition in the opening of the unloading tank, will make the unloading tank shorter and change the unloading position, resulting in trapped oil phenomenon, and then cause higher noise. In the normal repair process, the unloading groove may also be shortened due to the flat disc worn by the flat grinding. At this time, if it is not properly slender in time, it will also generate a large amount of noise. During the assembly process, the large unloading tank of the valve plate must be installed in the high pressure chamber of the pump, and the direction of its sharp corners must be opposite to the rotation direction of the cylinder. Otherwise, it will also bring more noise to the system.
2. Overflow valve noise
The relief valve is easy to produce high-frequency noise, which is mainly caused by the unstable performance of the pilot valve, that is, noise caused by air vibration caused by high-frequency oscillation of the pilot valve's front chamber pressure.
The main reasons are:
(1) Air is mixed in the oil and cavitation occurs in the pilot valve cavity to cause high-frequency noise. At this point, air should be drained in a timely manner and re-entry of outside air should be prevented.
(2) In the course of use, the needle valve is excessively worn due to frequent opening, so that the conical surface of the needle valve and the valve seat cannot be closely contacted. This leads to instability of the pilot flow and pressure fluctuation and noise, which should be promptly repaired or replaced.
(3) The pilot valve is unstable due to the fatigue deformation of the spring, causing large pressure fluctuations and noise, and the spring should be replaced.
3. Hydraulic cylinder noise
(1) There is air mixed in the oil or the air in the hydraulic cylinder is not fully drained, causing cavitation under the effect of high pressure and causing large noise. At this point, air must be drained in a timely manner.
(2) The cylinder head oil seal is too tight or the piston rod is bent. In the course of the movement, noise may also be generated due to the force. In this case, the oil seal or rod must be replaced in time.
4. Pipeline noise
Excessive bends in the tubing or loose clamps can also produce vibration and noise. Therefore, in the piping layout should be avoided as far as possible to avoid bending, the loose clips must be tightened in time.
Second, the hydraulic system vibration and noise causes and eliminate measures
1. The sources of vibration and noise cause many sources of vibration and noise in the hydraulic system, including mechanical systems, hydraulic pumps, hydraulic valves and pipelines. Vibration and Noise of Mechanical Systems The vibration and noise of mechanical systems are mainly caused by the mechanical drive system that drives the hydraulic pumps. The main aspects are as follows.
1) Unbalance of the rotating body In practical applications, most of the motors are driven by the coupling to drive the hydraulic pump. It is very difficult for these rotating bodies to achieve full dynamic balance. If the unbalanced forces are too great, they will rotate. Larger bending vibration of the shaft generates noise.
2) Improper installation Hydraulic systems often cause vibration and noise due to problems with installation. If the system piping is poorly supported and the foundation is defective or the hydraulic pump is not concentric with the motor shaft and the coupling is loose, these can cause significant vibration and noise.
2. The hydraulic pump (hydraulic motor) is usually the most important hydraulic element that generates vibration and noise in the entire hydraulic system. The reason why the hydraulic pump generates vibration and noise is due to the mechanical vibration on the one hand and the liquid pressure flow on the other hand. Accumulation caused by changes.
1) Cycle change of pressure and flow of hydraulic pump
Hydraulic pump gears, vanes and chokes are used in the process of sucking and pressing oil, so that the corresponding work produces periodic flow and pressure in the process, so that the corresponding working chamber generates periodic flow and pressure changes, thereby causing the pump The flow and pressure pulsations cause the components of the hydraulic pump to vibrate, and the vibration of the components causes the air that is in contact with it to generate a vibration that changes in density, and the sound pressure waves that generate the noise propagate out.
2) Cavitation phenomenon of hydraulic pump
When the hydraulic pump is working, if the resistance of the hydraulic oil suction pipe is too large, the hydraulic oil will not be able to fill the suction chamber of the pump too late, causing a partial vacuum in the suction chamber and forming a negative pressure. If this pressure just reaches the air separation pressure of the oil At that time, the original air dissolved in the oil will be precipitated in large quantities to form bubbles in a free state. With the rotation of the pump, the oily liquid with bubbles will be transferred to the high pressure area, and the bubbles will be reduced due to high pressure. Cracked and disappeared, forming a high local high-frequency pressure shock
3) Mechanical Vibration in Hydraulic Pumps
The hydraulic pump is composed of many parts. Due to manufacturing errors of the parts, improper assembly may cause vibration and noise of the hydraulic system. 3. Vibration of hydraulic valves and noise generated by noise hydraulic valves. Due to valve types, conditions of use, etc. The specific circumstances vary. According to the reasons for its occurrence can be roughly divided into two major categories of mechanical sound and fluid sound.
1) Mechanical sound
Most of the hydraulic valves are composed of spools, valve bodies, control parts, fasteners, and seals. He uses the external force to make the spools move. The spool moves to the corresponding position to change the fluid flow. Work requirements. During this process, the mechanical contact of the movable parts in the valve generates noise.
2) Fluid sound
As the hydraulic valve performs throttling, reversing, and overflowing, it causes various changes in the flow, direction, and back pressure of the fluid in the valve body, resulting in vibration of the wall surfaces of the valve member and the pipe, thereby generating noise. According to the causes of pressure vibration, it can be divided into cavitation sound, flow sound, hydraulic shock sound and shock sound. Pipeline vibration and noise are mainly caused by the interaction of hydraulic components such as pumps and valves on the pipeline. Studies have shown that when the length of the pipeline is exactly equal to an integer multiple of half the wavelength of the vibration pressure, the pipeline will generate strong high-frequency noise.
In addition, the external source may also cause resonance in the pipeline; when the pipeline suddenly changes in cross-sectional area (rapid expansion and contraction or sharp turn), it will cause changes in the liquid flow, easy to produce turbulence and emit noise.
Preventing air from being mixed with oil The hydraulic system often has less noise for a certain period of time since the start of operation. After a certain period of time, the noise increases. If the hydraulic oil in the tank is observed at this time, the hydraulic oil may turn yellow, which is mainly due to the oil. The microbubbles are mixed in, so they change color. For this situation, measures are mainly taken from two aspects. One is to fundamentally solve the problem and prevent air from entering. The second is to eliminate the air mixed into the oil body as soon as possible.
The specific method is:
1 Pump suction pipe joints must be tightly sealed to prevent inhalation of air.
2 Reasonably design the fuel tank. Preventing cavitation in hydraulic valves The generation of cavitation in hydraulic valves is mainly done to minimize the suction resistance of the pump. Commonly used measures include the use of larger diameter suction tubes, large-capacity suction filters, and the need to avoid clogging of the oil filter; the pump's suction height should be as small as possible.
Preventing turbulent flow and swirling in the pipeline When designing the hydraulic system piping, the piping section should be avoided as much as possible from suddenly expanding or shrinking; if the curved pipe is used, the radius of curvature should be more than five times the diameter of the pipe. These measures can be taken. Effectively prevent the generation of turbulence and swirling in the pipeline.
Use an accumulator or muffler to absorb pressure pulsations in the pipeline
Pressure pulsation in the pipeline is the main cause of vibration and noise in the system. The accumulator is installed in the hydraulic circuit, which can effectively absorb the vibration, and installing the absorber in the vicinity of the vibration part can also effectively reduce the system vibration.
Avoid system resonance
Frequent vibration sources (such as hydraulic pumps, hydraulic motors, motors, etc.) in the hydraulic system may cause resonance in the bottom plate, pipes, etc., or cause resonance in the components such as pumps and valves. For this phenomenon, the inherent vibration frequency of the pipe can be changed by changing the length of the pipe, and the change of the installation position of some valves can be eliminated.
Vibration isolation
For the main vibration source (pump, motor) in the hydraulic system, rubber pads or springs are often used to isolate it from the bottom plate (or fuel tank). The method of isolating the vibration source on the bottom plate and the entire system can also be used. These can receive good vibration and noise reduction effects.
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