Construction machinery hydraulic plunger pump noise analysis

When a construction machinery used in the hydraulic plunger pump in the maintenance operation of excessive noise, this is the pump will be damaged symptoms.

Hydraulic plunger pump (hereinafter referred to as the pump) noise has the following seven cases.

1. Inherent noise of the pump

Pump original inherent noise is the pump manufacturing technology has not yet reached the "robustness" requirements. For the working mode of the pump, every rotation of the pump spindle, each plunger in the pump for a cycle of oil suction to oil pressure. With the plunger in the complete suction pressure oil flow in the process, when the plunger hole on cylinder body cavity from the oil absorption window on the valve plate is full after the rotating transition to a row of oil from the oil, plunger hole cavity full of low pressure oil to the valve plate in front of the window on the high pressure oil oil discharge moment (see figure a, Japanese kawasaki K3V pump valve disk, for example), window of the high pressure oil discharge of oil from a ` secondary booster beforehand hole and triangle throttle slot into the plunger cylinder body hole cavity to increase oil pressure cavity, forming traffic flow backward. As the column sierra and backward flow of pressurization, plunger cylinder body hole cavity pressure rises to the oil pressure and oil discharge cavity after balance, plunger under the push of inclined plate, piston movement downward pressure oil flow into the cylinder with window, plunger oil discharge due to the effect of impedance of the fluid resistance, oil discharge system pressure of shock resistance, plunger cylinder body hole cavity pressure overshoot. When drainage after completion of plunger plunger cylinder body hole cavity after the discharge of oil window, enter the flow table cover area, plunger cylinder body hole cavity also listed part without emptying the overshoot of the dead volume pressure oil, due to the valve plate cover area theta 1 point of view, plunger and a continued compression stroke, the plunger cylinder body hole cavity die pressure oil volume of listed more overshoot. When the cylinder block plunger hole chamber is rotated to the oil suction window, a pressure release process is completed to enable the oil pressure in the cylinder block plunger hole chamber to be released to balance with the low pressure oil in the oil suction window. The instantaneous release of the overshoot dead volume high pressure oil in the cylinder body plunger hole cavity causes a liquid explosion. The continuous pressure transient liquid explosion in the nine-plunger hole cavity is a stable high-pitch sound, and each pump has a high or low liquid fall sound. Hydraulic pump manufacturers all over the world adopt various forms of noise reduction units in the pressure transition area of the distribution plate. The traditional methods, such as "triangle throttle groove", "discharge hole" and "inclined groove", have not solved the fluid noise caused by oil fluctuation of pump output pressure satisfactorily. For the high pressure pump with large displacement and sudden change of pressure used in construction machinery, the liquid explosion noise generated by overshooting oil pressure relief in dead volume area is particularly strong.

2. Cavitation noise

Hydraulic oil containing bubble, bubble oil drawn into cylinder with a hole, the piston in the cylinder hole hydraulic pressure oil into the cylinder valve discharge of oil below the window, under the effect of high pressure, the oil will pop the bubbles burst, almost the same size of the bubbles is high concentrated again after sudden demise, creates a strong detonation gas, generated when the bubble burst another high pitch noise, sends out a shrill scream. This strident noise is varying with the pump pressure value. When the pump output pressure reaches the highest, this noise decibel is also higher, when the pump pressure drops, this noise also with the decline.

The noise the pump makes when it takes in small amounts of air sounds like a rattle, a bit like bearing damage. When the pressure of the pump rises to a high pressure, it makes a very strange noise of pounding and bursting.

3. Mechanical noise

Pump mechanical noise is the main part of the main pump shaft and engine over the damage. The pump bearing.

If the pump spindle is different from the output shaft of the engine or the core is dead, the elastic coupling damage and loose bolt on the coupling block will produce noise.

If it is the sound of bearing damage will be issued a continuous breakdown sound. As the speed of the pump increases, the noise increases. Bearing damage, pump will appear shaking.

Pump mechanical noise is audible to the human ear, the best way is at low speed pump operation, industrial stethoscope or through the screwdriver in various parts of the pump listening,

Sudden noise

Pump but a sudden noise, it is necessary to immediately stop the pump operation, this is the pump parts have been damaged.

The plunger of the inclined shaft pump is broken or the plunger slipper of the inclined disk pump falls off, and the return disk is broken. The noise of this phenomenon is accompanied by the pump every turn and ring a continuous loud impact noise. It's like someone set off firecrackers inside the pump. At the same time accompanied by the pump P - mouth pressure hose pulsation phenomenon.

But when there is a sudden noise, the most important thing is not to let the hydraulic system pressure rise, because the pump shell parts of the broken metal slag block will accompany the pressure oil into the system. Pump sudden noise is terrible, it is not just the damage of the pump, broken pieces of metal slag but into the hydraulic system, is not clear, the hydraulic system caused lifelong damage.

5. Noise generated after pump maintenance

After maintenance, the pump will make more noise after installation and use than before the pump is not repaired. Reasons for this are as follows:

The rubber hose at the suction end of the pump starts to harden. When installing the pump, the rubber hose at the oil-suction side of the pump is oscillated greatly, leading to loose air leakage at the connection point between the rubber hose and the hard tube.

2) the second is the improper assembling method; the two cylinders of the double pump are symmetrical; the resonance noise occurs;

3) the bearings are of special type and high precision, and shall not be used with ordinary bearings.

1. Parts that are replaced have quality problems. The accuracy of the fit between parts is low.

Is a pair of friction pair arc surface offset between cylinder and valve plate, causing excessive oil leakage noise between friction pairs.

㈥ is inclined shaft of pump flow plate of new and old pump on the back cover variable sliding arc bias, cause valve plate of high pressure between the inlet and pump back cover on the back surface leakage in high pressure area, gas loss in the noise. The backside of the new distributor plate of the swash plate pump and the pressure area of the back cover of the old pump will also appear the same failure and noise.

6. Noise occurs in the pump after replacing the hydraulic oil

This noise is the new change of the oil in the air is not fully escape, when pump pharynx into the bubble, is under the action of high pressure of the pump outlet, the bubbles will be caused by a ruptured pressure gas organ sound suddenly, another reason is that the poor quality of the new change of the hydraulic oil, for a long time, the oil of antifoaming additive oxidizing or oil in the adverse effects produced by a variety of chemical additives are incompatible, not eliminate the oil in the air.

Any brand of mineral hydraulic oil contains about 10 percent air. This air is present in oil hydraulics in two ways, one in the form of bubbles, the other in the form of molecules dissolved in liquid, which cannot be seen. The increase in liquid volume is not noticeable.

7. Gradual noise

In the long - term use, the noise level of the pump increases from small to large. Valve is the valve plate and cylinder surface wear, valve plate with cambered surface and cylinder flow static pressure oil film is balance, static pressure in the oil film of oil containing metal particles can produce erosion wear, long-term washout wear will flow on the plate surface, produce certain width of the wear area, inner ring and outer ring with flow window curve change occurs surface xuan, from micro leakage to large leakage, the process of throttling noise can be from small to strong.

The "cavitation" noise caused by the suction of the pump is increased by small noise along with the extension of the working time.

Some people think that the oil pump suction side pipe does not leak, there will be no air infiltration, this is a mistake. From the principle of fluid mechanics and atmospheric pressure, when the pump does not work, the pressure difference between the pump suction port side and the atmosphere is zero, the liquid flow in the pump suction port pipeline is in a state of equilibrium, no oil leakage. When the "variable pump" is in operation, the fluid flow rate in the suction pipe of the pump is in a state of fast and slow. When the pump's "variable characteristic" determines that the pump's swing Angle changes from zero to the maximum Angle, the time difference between the change of the oil in the pump suction pipe from the static state to the rapid flow state, the liquid flow (liquid resistance) cannot meet the demand of the pump, and a very large siphon phenomenon (that is, the folk said suck force) is generated. Pump suction mouth when sucking phenomenon, also can from the rubber tube and hard tube interface sucked into the air and cavitation phenomenon.

When the flow velocity in the pump suction port pipe exceeds the limit, (the international standard is steady flow 0.5m/s, the absolute pressure is not less than 0.8m /s [1], and the actual flow velocity at the pump suction port can reach up to 2.m/s turbulent state,). The suction side of the pump will be negative below the atmospheric pressure, so there will be no enough pressure to accelerate the liquid flow into the pump rotary assembly, it will produce siphon phenomenon, as long as the pump siphon phenomenon, the life of the pump is to life.

8. Harm of cavitation noise

Pump in operation, if the flow of local area (export) is the pressure of the pump for some reason, the absolute pressure pumping liquid down to the temperature of liquid pressure, liquid at the begin to boil, to produce a large amount of steam, bubble formation, when contains a lot of bubbles in the liquid flowing through the cylinder block with high lateral flow window, air causing bubbles around the high pressure fluid has narrowed sharply, the bubbles burst crushed, this process can produce high temperature. According to the calculation, when the bubble from zero pressure is compressed to 3000 psi (207 bar), the temperature can rise up to 1149 ℃. [2] high temperature is the main reason for oil burning to form resinous substances and rapid oxidation degradation and deterioration of oil.

Condensed during the bubble burst at the same time, the liquid particle filling holes at high speeds, in this moment have a strong impact, and with the impact of the high frequency on metal surface, impact stress of tons per square inch, this hole burst of energy release will "bite" metal surface, like a home as a hammer and chisel carved stone carving. When this hydraulic impact occurs on the metal side wall of the valve plate, the bubble will burst when it hits the cylinder wall. At this time, the pressure is extremely instantaneous, and the local hydraulic impact has the effect of denudation on the metal surface. Gradually form pitting on the surface of metal parts. In severe cases, small pieces of metal surface will fall off and pits will appear (see figure 3 and figure 4). This phenomenon is called cavitation. Pump life will be shortened if cavitation is present for a long time.

Cavitation fault judgment method:

When the pump is under high pressure, it is used to grip the high-pressure rubber tube surface of the pump, and recognize whether the fluid in the tube vibrates when flowing.

2) when the pump is under high pressure, listen to the noise of explosion of the pump casing at the pump suction port;

3) separate the hydraulic oil tank cover, the excavator with big and small arms straight, and lift the bucket up quickly from the ground, and observe whether the oil bubbles come out.

Any kind of noise is harmful to the pump. Pump as long as there is excessive noise, it is necessary to maintain the pump, do not wait until the pump completely failed before maintenance, then may be too much loss.