What are the causes of noise in Niigata plunger pumps and what are the solutions?

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We know that all types of piston pumps generate some level of noise; the difference lies in the intensity of that noise. If the noise is too loud, it will cause noise pollution and interfere with the staff. Today, taking the Nippon Precision plunger pump as an example, we will discuss the reasons for noise generation in such pumps and the available solutions. When the NACHI-Fujikoshi hydraulic piston pumps used in construction machinery produce excessive noise during operation, it is a sign that the pump is about to fail. There are 8 situations in which the NACHI Fugaku hydraulic plunger pump (hereinafter referred to as the pump) generates noise. 1. Inherent noise: The presence of inherent noise in NACHI and Fujioka hydraulic piston pumps indicates that the pump manufacturing technology is not yet at the required level. In terms of the pump’s operation mode, with each rotation of the pump’s main shaft, each plunger in the pump completes one cycle from suction to compression of fluid. During the process of distributing oil for suction and compression, when the excess high-pressure oil in the plunger cavity of the cylinder body is suddenly released, a fluid explosion occurs. These continuous pressure fluctuations in the plunger cavity that result in fluid explosions produce a steady high-pitched sound; every pump generates such a sound, with the intensity of this sound varying from one pump to another. Hydraulic pump manufacturers around the world employ various types of noise reduction units in the pressure transition area of the distribution plate. From the traditional “triangular throttle groove type” to methods such as the “unloading hole type” and “inclined groove type”, none of these have successfully resolved the fluid noise caused by fluctuations in the pressure oil output by the pump. For high-displacement high-pressure pumps with sudden pressure changes used in construction machinery, the fluid explosion noise generated when the dead volume area causes pressure relief is even more intense. 2. Cavitation noise: When bubbles are present in the hydraulic oil, the oil containing these bubbles is drawn into the cylinder bore. The plunger presses the oil within the cylinder bore toward the oil discharge ports on the cylinder block’s distribution plate. Under high pressure, these bubbles burst suddenly; bubbles of nearly identical size, after being concentrated by the high-pressure oil, also burst abruptly, resulting in intense shock waves. Another type of ultrasonic noise produced when bubbles burst emits a sharp, piercing whistling sound. This sharp, harsh noise varies with the pressure fluctuations of the pump. This noise is also at its highest when the pump’s output pressure reaches its maximum ； When the pump pressure drops, this noise fades away. The noise produced when the pump draws in a small amount of air sounds like a \"clicking\" sound, somewhat similar to the sound of damaged bearings. When the pump’s pressure rises to high levels, a very strange noise of pounding and bursting is produced. 3. Main sources of mechanical noise in a mechanically noisy pump: the coupling between the pump’s main shaft and the engine ； At the bearing. Mechanical noise can occur if the pump’s main shaft is not aligned with the engine’s output shaft or if there is binding, if the elastic coupling is damaged, or if the bolts are loose. Damaged bearings will produce a continuous humming sound; the higher the pump’s speed, the louder the noise, and the pump will also start to vibrate. The mechanical noise of the pump is audible to the human ear; when the pump is running at low speed, it can also be heard at various parts of the pump using an industrial stethoscope or a screwdriver. 4. Sudden noise refers to the noise that occurs when the plunger of an inclined-axis pump breaks, or when the plunger shoe of an inclined-disc pump detaches or the return plate cracks. It is a continuous, loud knocking noise that occurs once per rotation of the pump, similar to the sound of firecrackers. Once sudden noise is detected from the pump, it must be stopped immediately to prevent the fault from worsening. The most important thing is to prevent the pressure in the hydraulic system from rising, as metal debris resulting from the fragmentation of parts inside the pump casing can enter the system along with the pressurized oil. This debris cannot be completely removed, and it will cause permanent damage to the hydraulic system. 5. The noise level of the pump after maintenance is higher than before repair. The reasons for this are: (1) If the suction hose of the pump hardens and is subjected to significant movement during installation, the connection between the hose and the hard pipe may become loose, resulting in air leakage. (2) If the assembly method is incorrect, and the holes in the front and rear (or left and right) cylinder blocks of the twin pump are symmetrical, resonant noise will occur. (3) Noise can also be generated if the clearance of the replaced bearing is excessive. Pump bearings require a high precision grade (bearings with high load capacity); ordinary bearings cannot be used. (4) The quality of the replaced parts is problematic; the fit accuracy level of these parts is low, which can result in resonance noise at operating frequencies. (5) The offset of the arc surfaces of the friction pair between the cylinder block and the valve plate can cause excessive noise due to oil leakage between the friction pairs. (6) The offset between the new distribution plate of the inclined-shaft pump and the variable sliding arc on the rear cover of the old pump causes planar leakage in the high-pressure area between the high-pressure port on the back of the distribution plate and the pump’s rear cover, resulting in aerodynamic noise. The same noise can also occur in the area where the back of the new distribution plate of the swash plate pump presses against the rear cover of the old pump. 6. Reasons for noise after oil change: The air contained in the newly installed oil has not been fully expelled; when the pump draws in bubbles, under the high pressure at the pump outlet, these bubbles are suddenly compressed and burst, resulting in a pneumatic explosion sound ； The newly replaced hydraulic oil is of poor quality and has been stored for a long time; the defoamers in the oil have oxidized, or various chemical additives present in the oil have caused adverse reactions, resulting in its inability to remove air from the oil. 7. Gradual noise increase (1) Over time, the noise level of NACHI Fujiyama hydraulic piston pumps increases from low to high. The reason is that the distribution surface of the distributor plate wears out against that of the cylinder block. A hydrostatic oil film maintains equilibrium between the curved surface of the distributor plate and the cylinder block’s distribution surface; however, if metal particles are present in this oil film, abrasive wear occurs. Over time, this abrasive wear creates wear areas of a certain width on the curved surface of the distributor plate, causing changes in the curvature of the inner and outer edges of the distribution openings. As a result, leakage increases in severity, and the throttling noise produced also becomes louder. (2) The suction rubber hose of the NACHI Fujikoshi hydraulic plunger pump ages, allowing air to be drawn in at the connection between the hose and the hard pipe. The air leakage increases from none to slight to excessive, and the \"cavitation\" noise caused by the pump drawing in air grows louder as operating time increases. It is a mistake to think that if there is no oil leakage in the pipeline on the pump’s suction side, then no air will get in. When the flow velocity in the pipeline at the pump’s suction port exceeds the specified limits (the international standard calls for a steady-flow condition with an oil flow rate of 0.5 m/s and an absolute pressure of not less than 0.08 MPa; in practice, the oil flow rate at the pump’s suction port can reach up to 2 m/s, resulting in a turbulent flow state), the absolute pressure on that side of the pump will be lower than atmospheric pressure and thus negative. In such a situation, there is not enough pressure to force the liquid flow into the rotating components of the pump, which leads to a siphoning effect – a condition that can be fatal to the pump. 8. Cavitation noise: When operating, if the absolute pressure of the liquid in certain areas of the flow path of a NACHI-Fujikoshi hydraulic piston pump – such as at the pump outlet – drops to the vaporization pressure at that temperature, the liquid will vaporize and large amounts of vapor will form bubbles. When this liquid containing many bubbles passes through the high-pressure area outside the valve ports in the cylinder block, the high-pressure liquid causes the bubbles to shrink rapidly until they burst suddenly, generating high temperatures. According to available data, when bubbles are compressed from zero pressure to 20.7 MPa, the temperature can rise to 1149°C. High temperatures cause the oil to burn, producing resinous substances that accelerate the oxidation and deterioration of the oil.