No. 6007, zhenpu road, xiepu town, zhenhai district, Ningbo
1. Pressure loss
Due to the viscosity of liquid and the inevitable friction when it flows in the pipeline, some energy must be lost in the process of liquid flow.This part of energy loss is mainly manifested as pressure loss.
There are two kinds of pressure loss: the along loss and the local loss.The loss along the path is the pressure loss due to friction when the liquid flows over a distance in a straight pipe with the same 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 path and the local loss.Due to the inevitable existence of pressure loss, so the rated pressure of the pump is slightly greater than the maximum working pressure required by the system, the maximum working pressure required by the system can be generally multiplied by a factor of 1.3~1.5 to estimate.
2. Flow loss
Static balance valve in the hydraulic system, the pressure components have a relative movement of the surface, such as the cylinder internal surface and piston external surface, because there is 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 through the gap to the low pressure area and cause leakage.At the same time, due to the hydraulic component seal is not perfect, some of the oil will leak to the outside.This leakage results in a decrease in actual flow, which is what we call flow loss.
Flow loss affects the speed of movement, and leakage is difficult to absolutely avoid, so the rated flow of the pump in the hydraulic system is slightly greater than the maximum flow required when the system is working.It can also be estimated by multiplying the maximum flow required for the system to work by a factor of 1.1~1.3.
3. Hydraulic impact
Reason: the movement of fluid due to inertia and some hydraulic components reaction action is not sensitive enough to produce instantaneous pressure peak, called hydraulic impact.The peak can exceed several times the working pressure.
Harm: cause vibration and noise;Make the relay, sequence valve and other pressure components have the wrong action, even cause some components, sealing device and pipeline damage.
Measure: find out the impact reason to avoid the rapid change of liquid flow velocity.Delay the time of velocity change, estimate the peak pressure, and take corresponding measures.If the flow reversing valve and electromagnetic reversing valve used together, can effectively prevent hydraulic impact.
Phenomenon: if the hydraulic system infiltration of air, the bubble in the liquid with the fluid flow movement to the area of higher pressure, the bubble under the action of higher pressure will quickly burst, resulting in local hydraulic impact, resulting in noise and vibration.In addition, the dynamic balance valve because of the bubble destroyed the continuity of liquid flow, reducing the oil flow capacity of the tubing, resulting in flow and pressure fluctuations, so that the hydraulic components bear impact load, affecting their service life.
Reason: hydraulic oil always contains a certain amount of air, which is usually dissolved in the oil or mixed with the oil in the form of bubbles.When the pressure is lower than the air separation pressure, the air dissolved in the oil separates and forms bubbles.When the pressure falls below the saturated vapor pressure of the oil, the oil boils and bubbles form.These bubbles intermingle with the oil and form a discontinuous state, which is called cavitation.
Location: lower than atmospheric pressure in oil suction port and oil suction pipe, easy to produce cavitation;When the oil flows through the narrow gap such as the throttle, the pressure will drop due to the increase of the speed, and cavitation will also occur.
Harm: the bubble moves with the oil to the high pressure area and cracks rapidly under the action of high pressure, resulting in a sudden decrease in volume, high speed flow of surrounding high pressure oil to replenish, causing local instant impact, a 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, try to avoid the narrow and sharp bend of the oil channel, to prevent the formation of low pressure area;Reasonable selection of parts materials, increase mechanical strength, improve surface quality, improve corrosion resistance.
Reason: cavitation is accompanied by cavitation. The oxygen in the air bubbles produced in cavitation will also corrode the surface of the metal components. We call this corrosion caused by cavitation phenomenon cavitation.
Location: cavitation can occur in oil pumps, pipelines, and other places with throttling devices, especially in oil pumps.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.
Advantages of hydraulic system: electric power unit
1. Small size and light weight;
2. High rigidity, high accuracy and fast response;
3, large driving force, suitable for heavy load direct drive;
4. Wide speed regulation range and various speed control methods;
5. Self-lubrication, self-cooling and long life;
6, easy to achieve security protection.
Disadvantages of hydraulic system:
1. Poor resistance to working fluid pollution;
2. Sensitive to temperature changes;
3. Potential leakage;
4. Difficult manufacturing and high cost;
5, not suitable for long-distance transmission and requires hydraulic energy.
Address：No. 6007, zhenpu road, xiepu town, zhenhai district, Ningbo