Archive for February, 2017

Noise Analysis of Hydraulic Piston Pump

When an engineering machine used in the hydraulic piston pump in operation to issue excessive noise, this is the pump will be damaged symptoms.
Hydraulic piston pump (hereinafter referred to as pump) have the following seven kinds of noise.
⒈ inherent noise pump
The original noise pump is the pump manufacturing technology to the present has not yet reached the “robustness” requirements. On the pump work, the pump spindle every rotation of a week, each pump plunger for a oil to the oil pressure of the cycle. Plunger in the completion of the distribution process of the suction oil, when the cylinder piston hole on the plate from the oil-absorbing plate on the window filled with oil cnc drill after the rotation to the oil discharge area transition, filled with low-pressure oil plunger cavity (See Figure 1, the Kawasaki K3V pump plate with the Japanese plate as an example), high-pressure oil within the oil discharge window from a `secondary pre-booster hole And the triangular throttling groove into the cylinder plunger cavity to increase the chamber oil pressure, the formation of flow intrusion impact (see Figure 2 left). As the plunger pulls out and increases the flow rate of the plunger, the pressure in the cylinder plunger cavity rises to balance the oil pressure in the oil discharge chamber. After the plunger presses the plunger, the plunger starts to move downward Pressure oil into the cylinder with the flow of the window, the plunger discharge oil resistance due to the role of liquid resistance, oil discharge by the system pressure of the anti-impact resistance, cylinder piston cavity pressure overshoot. When the plunger to complete the discharge, the cylinder plunger hole after the spin out of the oil discharge window, into the plate with the flow of the cover area, the cylinder piston cavity is still not part of the emptying of the overshoot pressure Dead volume pressure oil, because the angle of the plate on the angle θ1 obscured area, the plunger still has a compression stroke, so that the cylinder piston cavity of the remaining volume of dead volume pressure oil Steel Beam Drilling Machine more overshoot. When the cylinder plunger bore rotates to the suction window, a pressure relief process (see Figure 2 right) is performed to force the oil pressure in the cylinder piston bore to equalize with the low pressure oil in the suction window. Cylinder piston plunger cavity of the overshoot of the dead volume of high-pressure oil instantaneous pressure release caused by a liquid explosion, this nine plunger cavity of the continuous pressure transient burst is a stable high-pitched sound, each pump There is a high or low liquid waterfall sound. Hydraulic pump manufacturers around the world are in the distribution plate pressure transition area to take various forms of noise reduction unit. From the traditional “triangular throttle slot” to “leak hole” “oblique trench” and other methods, but are still not satisfactorily solve the pump output pressure fluctuations caused by fluid noise. For construction machinery used in the large displacement pressure of the high-pressure pump, dead volume area over-regulation of oil discharge pressure generated when the liquid explosion noise is particularly strong.

angle straightening machine

⒉ cavitation noise
When the hydraulic oil contains the air bubble, the oil with the bubble is sucked into the cylinder bore, the plunger presses the oil in the cylinder bore to press the oil discharge window in the cylinder flow distribution surface. Under the high pressure, the bubbles in these oil will Sudden collapse, the size of the bubble bevelling machine is almost the same concentration of high pressure and then sudden collapse, causing a strong gas explosion, bubble burst generated by another high-pitched noise, will issue a sharp ear-piercing Of the whistle. This sharp-hitting noise varies with the pressure of the pump. When the pump’s output pressure reaches its maximum, the higher the noise decibel, the lower the noise of the pump when the pump pressure drops.
When the pump inhales a small amount of air generated by the noise sounds like a rattling sound, a bit like bearing damage sound. When the pump pressure rises to high pressure, it produces a very strange blow to blow the noise.
⒊ mechanical noise
Pump the main parts of the mechanical noise ⑴ pump shaft and the engine took place at the damaged. ⑵ pump bearing Department.
If the pump shaft and the engine output shaft is not concentric or top dead, elastic connector damage and connector block loosening of the bolts will produce noise.
If it is bearing the sound of damage will be issued continuously buzzing sound. As the speed of the pump increases, so does the noise. Damage to the bearing, the pump will tremble.
Pump mechanical noise is the human ear can hear out, the best way is to run the pump at low speed, with industrial stethoscope or through the screwdriver in the pump parts of the clinic,
⒋ sudden noise
Once the pump has sudden noise, it must immediately stop the pump operation, this situation is the pump parts have been damaged.
Plunger pump plunger plunger piston plunger or broken off, the return disc disintegration. The noise of this phenomenon is a continuous loud noise with one revolution of the pump Hydraulic punching machines. Like someone in the pump body firecrackers. At the same time with the pump P port pressure hose pulsation phenomenon.
But the sudden emergence of noise, the most critical thing is not to allow the pressure of the hydraulic system increases, because the parts of the pump casing fragments of metal slag will be accompanied by pressure oil into the system. Pump sudden noise is terrible, it is not just the pump damage, broken metal slag block, but into the hydraulic system, can not be removed, the hydraulic system caused by the life-long harm.
⒌ pump maintenance after the noise
After the installation of the pump after the installation of the use of noise than the repair before the pump is even larger, the reasons for this happen:
(1) pump suction hose hardening, the installation of the pump, the suction side of the pump hose was substantially swing, so that hose and hard tube at the junction of loose air leakage occurs.
(2) Another is the improper assembly method, double-pump in front and rear (or left and right) two cylinder bore symmetry, there has been resonance noise.
(3) is the replacement of the bearing clearance excessive, the pump bearings are special models and high-precision level (large bearing capacity), can not use ordinary bearings.
(Iv) is the replacement of parts with quality problems, parts with the accuracy level is low, resulting in operating frequency resonance noise.
(V) is the cylinder and the distribution plate between the pair of friction pairs of arc surface bias, resulting in friction between the leakage of excessive oil noise.
(Vi) is a new valve plate with oblique axis pump and the old pump back cover variable sliding arc bias, resulting in distribution plate disc high pressure port and the back cover of the high pressure area plane leakage, air damage noise. The same fault and noise can be seen on the rear side of the new plate plate and the pressing area of ​​the old pump back cover.
⒍ replace the hydraulic oil pump noise
This noise is the new replacement of oil in the air is not fully escape, when the pump into the bubble of the bubble, the pump at the exit of the high-pressure effect, these bubbles will suddenly burst pressure caused by gas waterfall sound, the other The reason is the new replacement of poor quality hydraulic oil, storage for a long time, the defoaming additives in oil oxidation or oil in a variety of chemical additives are not compatible with the adverse reactions arising from the elimination of oil in the air effect.
Any brand of mineral hydraulic oil contains about 10% of the air. This air is in two ways exist in oil pressure, one is the existence of bubbles in the form of oil, the other is dissolved in the form of molecules in the liquid, is not visible. The volume increase of the liquid is not obvious.
7, the gradual noise
(I) the pump in the long-term use of the process, the noise from small to large. Is the distribution plate and the cylinder with the flow surface of the wear and tear, the flow plate with the cylinder and the cylinder surface is static pressure oil film balance, hydrostatic oil film containing metal particles such as when there will be erosion and erosion, long-term erosion and wear will A certain width worn area is formed on the arc surface of the flow distribution disc, and the curve curve of the inner and outer windows of the flow distribution window is changed, resulting in the process from microleakage to extra large leakage, and the throttle noise is also small to strong.
(2) the pump suction side of the hose aging, the air from the hose and the hard pipe connection was inhaled, air leakage from zero to micro-leakage and then to a process of over-leakage, pump inhaled air caused by “cavitation” This noise is small The noise increases with the extension of the working time.
Some people think that the pump suction port side of the pipeline does not leak, there will be no air infiltration, which is a wrong understanding. From the principles of fluid mechanics and atmospheric pressure, when the pump does not work when the pump suction side and the pressure difference between the atmosphere is zero, the pump suction pipe in the liquid flow is not in balance, no oil leakage. When the “variable pump” in the work, the pump suction pipe in the fluid flow rate is fast time and slow state. When the “variable characteristic” of the pump determines the pump’s swing angle changes instantaneously from zero degrees to the maximum angle, the flow (liquid resistance) in the pump suction pipe can not meet the requirement of the pump in the time difference from the quiescent state to the fast flow state Demand, then produce a very large siphon phenomenon (that is, the civil power). Pump suction mouth occurs when the phenomenon of force, it will be from the hose and the junction of the hard tube into the air and cavitation phenomenon.
When the flow rate in the pump suction port pipe exceeds the standard (the international standard for the steady flow state 0.5m / s, the absolute pressure of not less than 0.8bars [1], the reality of the pump side of the flow rate of up to 2. M / s turbulent flow state). The pump suction side will be below the atmospheric pressure is negative, then there will not be enough pressure to accelerate the flow into the pump rotating components, it will produce siphon phenomenon, the pump as long as the siphon phenomenon, that the life of the pump is to life.
8, cavitation noise hazards
In the operation of the pump, if the local area of ​​the flow-through portion (which is the pressure outlet of the pump) is, for some reason, the absolute pressure of the pumped liquid is reduced to the vaporization pressure of the liquid at that time, the liquid begins to vaporize there, A large amount of steam, the formation of bubbles, when a large number of bubbles of liquid flow through the cylinder outside the high-pressure area of ​​the flow window, the bubble around the high-pressure liquid bubble causes the bubble sharply reduced, these bubbles are suddenly broken pressure, this process will produce high temperature. According to the calculation, when the bubble is compressed from zero pressure to 3000Psi (207Bar), the temperature can be increased to 1149 ℃. [2] The high temperature causes the oil combustion, produces the resinous material, and causes the oil to oxidize quickly the degeneration main reason.
At the same time the bubble collapses, the liquid mass fills the hole at a very high velocity, producing a very strong impact at this instant and striking the metal surface with a high impact frequency drilling machine, the impact stress being several tons per square inch The release of energy from the breakage of a hole would “erode” the metal surface, just as the sculptor used a hammer and a chisel to carve a stone. When such a hydraulic shock occurs in the metal plate side wall, the bubble burst into the cylinder wall when the pressure instantaneous maximum, the resulting local hydraulic impact on the metal surface erosion effect. So that the surface of metal parts gradually formed pockmarks. Serious, it will make the metal surface of small pieces off, there small pits (see Figure 3 Figure 4), this phenomenon is called cavitation. If the long-term cavitation, pump life will be shortened.
Cavitation fault diagnosis method:
(I) When the pump is in a high pressure state, it is used to hold the pump high-pressure glue pipe surface, and sense whether the liquid in the pipeline is vibrating when flowing.
(2) When the pump is in a high-pressure state, in the pump suction port side of the pump shell to hear whether the flap of the explosion noise.
(3) open the hydraulic tank fuel tank cover, the size of the excavator arm stretched flat, the bucket from the ground quickly rise to observe whether the oil inside the tank a large number of bubbles escape.
9, concluding remarks
Any kind of noise, the pump is hazardous. As long as there is excessive noise pump, it is necessary to repair the pump, do not wait until after the failure of the pump completely repaired, then the loss may be too large.