Common abnormal phenomena in hydraulic system of construction machinery

The pressure loss

Because liquids are viscous and have friction when flowing in pipelines, they must lose some energy in the process. This part of energy loss is mainly manifested as pressure loss.

There are two kinds of pressure loss: the loss along the way and the loss in the place. Along loss is the pressure loss due to friction when the liquid flows through a distance in a straight pipe with constant diameter. Local loss is the pressure loss caused by sudden change of section shape of pipeline, change of flow direction or other forms of flow resistance. The total pressure loss is equal to the sum of the loss along the way and the local loss. Due to the inevitable existence of pressure loss, the rated pressure of the pump should be slightly greater than the limit working pressure required by the system. Generally, the system can be required to work the limit working pressure times a coefficient of 1.3~1.5 to estimate.

Flow loss

In the hydraulic system, each pressed element has a relative movement of the surface, such as the inner surface of the hydraulic cylinder and the outer surface of the piston, because there is a relative movement, so there is a certain gap between them. If one side of the gap is high pressure oil and the other side is low pressure oil, the high pressure oil will flow to the low pressure area through the gap and cause leakage. At the same time, because the hydraulic element seal is not perfect, part of the oil will leak to the outside. The actual flow loss due to this leakage is what we call a flow loss.

Flow loss affects motion speed, and leakage is difficult to avoid, so the rated flow of the pump in the hydraulic system is slightly greater than the limit flow required when the system works. It is also usually possible to estimate the limit flow required for the system to work by multiplying a factor of 1.1 to 1.3.

Hydraulic impact

Reason: the actuator element reversing and the valve closed so that the flow of liquid due to inertia and some hydraulic components of the reaction action is not sensitive enough to produce instantaneous pressure peak, said hydraulic impact. Its peak can exceed the working pressure several times.

Harm: cause vibration, produce noise; Make relay, sequence valve and other pressure components produce wrong action, and even cause some components, sealing device and pipeline damage.

Measures: find out the cause of the impact and avoid the sharp change of flow velocity. Delay the time of velocity change, estimate the pressure peak, and take corresponding measures. If the flow valve and solenoid valve used together, can effectively prevent hydraulic impact.

cavitation

Phenomenon: if the air permeates into the hydraulic system, the bubble in the liquid moves to the area of high pressure with the liquid flow, the bubble will burst quickly under the action of high pressure, resulting in local hydraulic impact, resulting in noise and vibration. In addition, due to the bubble destroyed the continuity of fluid flow, reducing the tubing capacity, resulting in flow and pressure fluctuations, hydraulic components bear impact load, affecting their service life.

Reason: Hydraulic oil always contains a certain amount of water, usually dissolved in the oil, but also in the form of bubbles mixed in the oil. When the pressure is lower than the air separation pressure, the air dissolved in the oil is separated and bubbles are formed. When the pressure drops below the saturated vapor pressure of the oil, the oil boils and bubbles form in large Numbers. These bubbles mix with the oil to form discontinuities, a phenomenon known as cavitation.

Position: lower than atmospheric pressure in the oil suction port and oil suction pipe, easy to produce air cavitation; Cavitation will also occur when oil fluid flows through narrow crevices such as throttles and pressure drops due to the increase of velocity.

Harm: the bubble moves with the oil to the high pressure area and breaks rapidly under the action of high pressure, resulting in a sudden decrease in volume and high speed flow of high-pressure oil around to replenish, causing local instant impact, sharp rise in pressure and temperature, and strong noise and vibration.

Measures: To correctly design the structural parameters of the hydraulic pump and the suction pipe line of the pump, to avoid the narrow and sharp bend of the oil channel as far as possible, to prevent the generation of low pressure area; Reasonable selection of machine materials, increase mechanical strength, improve surface quality, improve corrosion resistance.

Cavitation phenomenon

Reason: Cavitation occurs with cavitation, and the oxygen in the bubbles generated in the cavitation also corrodes the surface of the metal element. We call this corrosion caused by cavitation erosion.

Location: Cavitation can occur in oil pumps, pipelines and other places with throttling devices, especially in oil pumps. This phenomenon is very common. Cavitation is one of the causes of various faults in hydraulic system, especially in high speed and high pressure hydraulic equipment. Hazards and measures are the same as cavitation phenomenon.

Want to know more relevant information, you can leave a message on line or directly dial the mechanical and electrical hydraulic system manufacturer hotline consultation!