Analysis And Countermeasures Of Several Noises Of Hydraulic Piston Pumps

1. Mechanical noise

The first part of the pump to declare mechanical noise is at the coupling bearing between the pump spindle and the engine. Mechanical noise will occur if the pump spindle is not concentric or the engine output shaft is not concentric or dead, the elastic coupling is damaged or the bolts are loose. Bearing damage will announce a series of "whoosh" sounds, the higher the speed of the pump, the louder the noise, and the pump will also show a shivering scene.

The mechanical noise of the pump can be heard by the human ear, and when the pump is running at low speeds, it can be heard in various parts of the pump with an industrial stethoscope or through screwdriver.

2. Cavitation noise

When the hydraulic oil is rich in bubbles, the oil with bubbles is sucked into the cylinder bore, and the plunger squeezes the oil into the oil discharge window of the cylinder distribution plate in the cylinder bore, and these bubbles will be squeezed and cracked under the effect of high pressure, and the bubbles of the same size are concentrated by the high-pressure oil and then suddenly collapse, which will constitute a weak gas explosion. Another type of ultra-high-pitched noise that occurs when a bubble bursts announces a high-pitched whistling sound. This sharp, high-pitched noise changes as the pressure of the pump fluctuates. This noise is also highest when the pump output pressure reaches its highest, and when the pump pressure is reduced, this noise is weakened.

The noise that occurs when the pump draws in a small amount of air sounds like a "click, click" sound, a bit like the sound of a damaged bearing. When the pressure of the pump rises to high pressure, there is a very obscure thumping noise.

3. Sudden noise

The sudden noise when the plunger of the inclined shaft pump cracks or the plunger slipper of the swash plate pump falls off or the return disc is broken, which is a series of loud collision noises that sound once every revolution of the pump, just like a firecracker.

Once the pump shows sudden noise, it is necessary to stop the pump immediately to prevent the problem from further expanding. The most important thing is not to let the pressure of the hydraulic system rise, because the metal slag block of the broken parts in the pump casing will follow the pressure oil into the system, which cannot be completely removed, and will cause lifelong damage to the hydraulic system.

4. Intrinsic noise

The inherent noise of the pump indicates that the pump production skills have not yet reached the request, and for the pump working mode, each plunger of the pump makes a cycle of suction to pressure oil every week that the pump spindle rotates. In the process of completing the distribution of suction and pressure oil in the plunger, the overshoot dead volume of high-pressure oil in the plunger orifice cavity of the cylinder block will constitute a liquid explosion when the pressure is released in an instant, and the pressure transient liquid explosion of the plunger orifice cavity is a stable high-cavity sound, and each pump has a high or low liquid waterfall sound. Hydraulic pump manufacturers all over the world are adopting various forms of noise reduction units in the pressure transition area of the distribution plate. From the traditional "triangular saving trough type" to "unloading hole type", "inclined ditch type" and other methods, but still do not satisfactorily solve the fluid noise caused by the fluctuation of the pump output pressure oil. Regarding the high-pressure pump with large displacement pressure abrupt change used in construction machinery, the liquid explosion noise that occurs when the overshoot oil is depressurized in the dead volume area is stronger.

5. Noise after oil change

Factor: The air in the new replacement fluid does not escape sufficiently, and when the pump sucks in the air bubbles, under the effect of high pressure at the pump outlet, these bubbles will be contracted and burst to form an air explosion. The newly replaced hydraulic oil has poor quality, long storage time, oxidation of defoamer in the oil or adverse reactions of a variety of chemical additives in the oil, which can no longer have the effect of eliminating the air in the oil.

6. Noise after patching

The noise of the piston pump after repair is greater than that before repair, and the factors are: (1) if the pump oil suction hose is hardened and the device is greatly shaken, the connection between the hose and the hard pipe will be loose and leaking; (2) if the installation method is improper, the front and rear or the left and right cylinder holes in the duplex pump are symmetrical, and the resonant noise will appear; (3) if the replacement bearing clearance is overrun, noise will also occur. (4) The quality of the replaced parts is questionable, and the matching accuracy grade of the parts is low, and the resonance noise of the operating frequency will occur; (5) The arc plane of the cylinder block and the distribution plate is offset by the conflicting pair, and the excessive noise of oil leakage between the conflicting pairs will occur; (6) The variable sliding arc offset on the new distribution plate of the inclined shaft pump and the back cover of the old pump will constitute the plane leakage in the high-pressure area between the high pressure port on the reverse side of the distribution plate and the back cover of the pump, and the gas loss noise will occur. The reverse side of the new distribution plate of the swash plate pump will also show the same noise as the compression area of the back cover of the old pump.

7. Cavitation noise

If the pump is in operation, if it flows through some parts of the area, such as the pump outlet liquid, when the definite pressure is reduced to the vaporization pressure at the temperature, the liquid will vaporize and form a bubble, when the liquid rich in many bubbles flows through the high-pressure area outside the distribution window of the cylinder block, the high-pressure liquid will make the bubbles decrease sharply until it breaks and the high temperature occurs. The high temperature incinerates the oil to form a resinous substance, which accelerates the oxidation and transformation of the oil.

When the bubble bursts and condenses, the liquid particles fill the cavities at a very high speed, and in an instant, they will impact the metal surface at a very high frequency, causing a large impact stress, which can "eat" the metal surface, just like carving a stone with a household hammer or chisel. When this hydraulic impact occurs on the metal side wall of the distribution plate, the bubble bursts when it hits the cylinder wall, and the instantaneous pressure is extremely great, which has an erosion effect on the metal surface, so that the appearance of the metal parts gradually constitutes a pit, and in serious cases, it will make the metal surface fall off and present a small pit, and if this cavitation scene exists for a long time, the damage is great.

The method of identifying cavitation defects is as follows:

(1) When the pump is under high pressure, grasp the high-pressure hose of the pump with your hand and sense whether there is vibration when the liquid in the pipeline moves. When the pump is under high pressure, listen to the pump casing at the suction port of the pump to see if there is a popping noise.

(2) Disassemble the fuel filler cover of the hydraulic tank, dig the motor arm and stick flattened, and the bucket rises quickly from the ground to observe whether there are many bubbles escaping from the oil in the tank.

(3) As long as the pump presents overrun noise, the pump should be repaired in time, if it is repaired after the pump fails, the loss is too great.

8. Progressive noise

(1) In the process of long-term use of the pump, the noise is from small to large. If the oil film is rich in metal particles, it will occur erosion and wear, and long-term erosion wear will constitute a certain width of wear area on the arc surface of the distribution plate, so that the inner ring and outer ring of the distribution window will change the arc curve, resulting in leakage from light to heavy, and the noise saving is also from small to large.

(2) The pump suction hose is aging, the air is sucked from the junction of the hose and the hard pipe, and the air will leak from zero to trace leakage and then to excessive leakage, and the "cavitation" noise formed by the pump after inhaling the air follows the extension of the working time from small to large.

If you think that if the pipe on the suction port side of the pump does not leak oil, there will be no air seepage, which is wrong.

When the flow rate in the suction pipe of the pump is exceeded, the pressure on the suction side of the pump will be lower than the atmospheric pressure and be negative, and the unsatisfied pressure at this moment will accelerate the flow into the rotating components of the pump, and the siphon scene will occur, which is fatal to the pump.