What is the cause of the noise generated by the  Hydraulic Pumps  at work? China Hydraulic Pumps Manufacturers, Suppliers & Zhejiang Yongling Hydraulic Machine Co , Ltd Analysis:

1. Noise of hydraulic pump

(1) The suction phenomenon is one of the main causes of excessive noise in hydraulic pumps. When air is mixed into the oil, it is easy to form cavitation in its high pressure area and propagate in the form of pressure waves, causing the oil to oscillate and cause cavitation noise in the system.

The main reasons are:

1. The oil filter of the hydraulic pump, the oil inlet pipe is blocked or the oil viscosity is too high, it can cause the vacuum degree at the oil inlet of the pump to be too high, so that the air infiltrates.

2. The oil seal on the shaft end of the hydraulic pump or pilot pump is damaged, or the oil pipe is not well sealed, causing air to enter.

3. The oil level in the fuel tank is too low, so that the hydraulic pump inlet pipe is directly evacuated.

When high noise occurs in the work of the hydraulic pump, the above parts should be inspected first, and problems should be solved in time.

(2) Excessive wear of the internal components of the hydraulic pump, such as the wear and tear of the hydraulic pump's cylinder and distribution plate, the rotor and the blade fittings, will cause serious leakage in the hydraulic pump. When the hydraulic pump outputs high pressure and small flow of oil, Generates flow pulsation, causing higher noise. At this time, the deflection angle of the variable mechanism of the pilot system can be appropriately increased to improve the effect of internal leakage on the output flow of the pump.

The piston of the hydraulic pump to control the flow will also be subject to local wear and tear, which will cause the piston to pulsate during the movement, which will cause the output flow and pressure of the hydraulic pump to fluctuate, which will cause greater vibration and noise at the pump outlet. At this time, the components with severe wear and tear can be subjected to brush plating research or replacement.

(3) The hydraulic pump flow plate is also one of the important components that is prone to noise. Due to surface wear or sludge deposits at the opening of the unloading tank during use, the distribution plate will shorten the unloading tank and change the unloading position, resulting in oil traps, which will cause higher noise. In the normal repair process, the distribution plate repaired by flat grinding will also have the effect of shortening the unloading groove. At this time, if it is not properly lengthened in time, it will also generate a large noise. During the assembly process, the large unloading groove of the distribution plate must be installed in the high-pressure chamber of the pump, and its sharp angle must be opposite to the rotation direction of the cylinder, otherwise it will bring greater noise to the system.

2. Noise from relief valve

The relief valve is prone to high frequency noise, which is mainly caused by the unstable performance of the pilot valve, that is, the noise caused by air vibration caused by the high frequency oscillation of the pressure in the front cavity of the pilot valve.

The main reasons are:

(1) Air is mixed in the oil, and cavitation is formed in the front cavity of the pilot valve, which causes high-frequency noise. In this case, exhaust air in time and prevent outside air from re-entering.

(2) The needle valve is frequently worn due to frequent opening during use, which makes the cone surface of the needle valve and the valve seat unable to closely contact with each other, resulting in unstable pilot flow, pressure fluctuations and noise, which should be repaired or replaced in time.

(3) The pilot valve's pressure regulating function is unstable due to fatigue deformation of the spring, which causes large pressure fluctuations and causes noise. At this time, the spring should be replaced.


Causes and elimination measures of vibration and noise of hydraulic system

1. 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 the mechanical system The vibration and noise of the mechanical system are mainly caused by the mechanical transmission system that drives the hydraulic pump, mainly in the following aspects.

1) Unbalance of slewing bodies In practical applications, most motors work through couplings to drive hydraulic pumps. It is very difficult to achieve complete dynamic balance of these slewing bodies. If the imbalance force is too large, it will rotate. When a large bending vibration of the shaft is generated, noise is generated.

2) Improper installation Hydraulic systems often cause vibration and noise due to installation problems. Poor support of the system's pipes and defects in the foundation or the misalignment of the hydraulic pump with the motor shaft and loose couplings will cause greater vibration and noise.

2.Hydraulic pumps (hydraulic motors) are usually the most important hydraulic components that generate vibration and noise in the entire hydraulic system. The reasons for the vibration and noise of hydraulic pumps are due to mechanical vibration on the one hand and fluid pressure flow on the other. Caused by accumulation changes.

1) Periodic change of hydraulic pump pressure and flow

The gears, blades, and plugs of the hydraulic pump are in the process of absorbing and pressing oil, so that the corresponding work generates periodic flow and pressure, and the corresponding working chamber produces periodic changes in flow and pressure, which in turn causes the pump The flow and pressure pulsations of the pump cause the components of the hydraulic pump to vibrate, and the vibrations of the components cause the air in contact with them to produce dense and variable vibrations, which in turn generates noise and pressure waves to propagate.

2) Cavitation in hydraulic pumps

When the hydraulic pump is working, if the resistance of the hydraulic oil suction pipe is too large, at this time, the hydraulic oil has no time to fill the suction chamber of the pump, causing a partial vacuum in the suction chamber and forming a negative pressure. If this pressure just reaches the oil's air separation pressure At this time, the air dissolved in the oil will be precipitated in large quantities to form free air bubbles. With the rotation of the pump, this oil liquid with air bubbles will enter the high-pressure area, and the air bubbles will shrink due to the high pressure. Rupture and disappear, forming a high local high-frequency pressure shock

3) Mechanical vibration in the hydraulic pump

The hydraulic pump is composed of many parts. Due to the manufacturing errors of the parts, improper assembly may cause vibration and noise of the hydraulic system.

 3. Vibration and noise of the hydraulic valve The noise generated by the hydraulic valve varies depending on the specific conditions such as the type of valve and the use conditions. According to the cause of its occurrence, it can be roughly divided into two categories: mechanical sound and fluid sound.

1) Mechanical sound

Most of the hydraulic valves are composed of valve core, valve body, control parts, fasteners, seals and other parts. He uses external force to move the valve core, and the valve core moves to the corresponding position to change the fluid flow. Work requirements. During this process, the mechanical contact of moving parts inside the valve generates noise.

2) Fluid sound

As the hydraulic valve performs throttling, reversing, and overflowing, the flow, direction, and back pressure of the liquid flow in the valve body are variously changed, which causes the valve and the wall surface of the pipe to vibrate, thereby generating noise. According to the cause of pressure vibration, it can be divided into cavitation sound, flow sound, hydraulic shock sound and vibration sound. Vibration and noise of the pipeline This is mainly caused by the interaction of the vibration of pumps, valves and other hydraulic components 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, external seismic sources may also cause pipeline resonance; when the cross-sectional area of ​​the pipeline changes suddenly (expanding or shrinking sharply or turning sharply), the liquid flow in it will change, and turbulence will easily occur and noise will be generated.

Preventing oil from mixing into the air The hydraulic system tends to have low noise during a certain period of operation. After a certain period of time, the noise increases. If you observe the hydraulic oil in the fuel tank at this time, you can find that the hydraulic oil turns yellow. This is mainly due to the oil Tiny air bubbles are mixed in, so the color changes. There are two main measures taken to deal with this situation. The first is to fundamentally solve the problem and prevent air from entering. The second is to remove the air mixed into the oil body as soon as possible.

The specific method is:

1 The suction pipe joint of the pump must be tightly sealed to prevent air intake;

2 Reasonably design the fuel tank. To prevent the cavitation of the hydraulic valve, the cavitation of the hydraulic valve is mainly used to reduce the suction resistance of the pump as much as possible. Common measures include using a large diameter suction pipe and a large-capacity suction filter, while avoiding clogging of the filter; the suction height of the pump should be as small as possible.

Prevent the occurrence of turbulence and swirl in the pipeline. When designing the pipeline of the hydraulic system, try to avoid sudden expansion or contraction of the pipeline section; if a curved pipe is used, its radius of curvature should be more than five times the diameter of the pipeline. These measures can be used. Effectively prevent turbulence and swirl in the pipeline.

Use accumulators or mufflers 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 in the hydraulic circuit can effectively absorb the vibration, and the damper near the place where the vibration occurs can also effectively reduce the system vibration.

Avoid system resonance

In the hydraulic system, vibration sources (such as hydraulic pumps, hydraulic motors, motors, etc.) often cause resonance in the bottom plate, pipelines, and other parts; or resonance of components such as pumps, valves, and other channels causes large noise. For this phenomenon, the natural vibration frequency of the pipeline can be changed by changing the length of the pipeline, and some valve installation positions can be changed to eliminate it.

Isolate vibration

For the main vibration source (pump, motor) in the hydraulic system, measures such as installing rubber pads or springs are often used to isolate it from the bottom plate (or fuel tank). Alternatively, the vibration source can be installed on the bottom plate to isolate it from the entire system. These can receive good vibration and noise reduction effects.

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