In modern construction machinery, basically can not be separated from the hydraulic working device, even if the main working device does not use hydraulic equipment, usually also need the hydraulic system to achieve some auxiliary work, so it is closely related to our life and work.
When it comes to the hydraulic system, it must mention the main pump, the birth of the pump is very early, the ancient equipment used to lift water is the earliest pump, such as China’s water wheel, Egypt’s chain pump.
Hydraulic transmission is widely used in various fields, known as “industrial muscle”, and in hydraulic transmission hydraulic pump is a power component, is the “source” of its power, especially into the era of mechanization, everywhere has its figure, the importance is self-evident.
A complete hydraulic system consists of five parts, namely power components, executive components, control components, auxiliary components and hydraulic oil.
The role of the actuator (hydraulic cylinder and hydraulic motor) is to convert the pressure energy of the liquid into mechanical energy, and drive the machine to make linear reciprocating movement or rotary movement.
Control elements (various hydraulic valves) control and regulate the pressure, flow and direction of liquids in the hydraulic system.
Auxiliary components include oil tank, oil filter, sealing ring, pressure gauge, etc. Hydraulic oil is the medium of energy transfer in the hydraulic system, mineral oil, synthetic hydraulic oil and so on.
The function of the hydraulic pump is to convert the mechanical energy of the power machine (such as electric motors and internal combustion engines, etc.) into the pressure energy of the liquid. The output flow can be adjusted according to the needs of the variable pump, the flow can not be adjusted called quantitative pump. Although the structure of different types of hydraulic pumps is very different, there are many common points in installation, use and maintenance, which may lead to failure if the operation is not standardized.
[Commonly used hydraulic pump types]
1, according to whether the flow can be adjusted can be divided into: variable pump and quantitative pump. The output flow can be adjusted according to the needs of the variable pump, the flow can not be adjusted called quantitative pump.
2, according to the pump structure commonly used in the hydraulic system is divided into: gear pump, vane pump and plunger pump 3 kinds.
【 Working principle of hydraulic pump 】
1. Gear pump
Gear pump has the characteristics of small size, simple structure, strong anti-pollution, cheap price, large leakage, large noise, large flow pulsation, and displacement can not be adjusted.
Gear pump is composed of two gears meshing with each other, when the motor or engine drives one of the gears, the other gear meshing with it will rotate at the same time.
The pair of gears rotate with each other, the gear teeth gradually break off on one side of the meshing teeth, and the volume of the sealing cavity increases, forming a local vacuum. The hydraulic oil in the oil tank is sucked in to fill the increasing volume under the action of atmospheric pressure. The sucked hydraulic oil fills the tooth groove, and with the tooth groove rotating, the oil is brought to the pressure oil chamber on the other side of the meshing zone. The two gear meshing lines separate the oil suction chamber and the oil pressure chamber, so that there is no hydraulic oil leakage between the oil suction area and the oil pressure area, and the gear constantly rotates to complete the oil suction and oil pressure process.
2, blade pump
Vane pump has the characteristics of uniform flow, smooth operation, low noise, high working pressure and volumetric efficiency, and complex structure.
Vane pump is formed by the rotor and the blade to form an eccentric structure, with the rotor in the drive shaft rotation, the lower end of the blade due to the role of spring or hydraulic oil, always maintain enough pressure, so that the blade tip can be close to the inner wall of the pump, in the rotation process, any two adjacent blades and the pump body enclosed into a closed space, closed space gradually becomes larger, The hydraulic oil is sucked into the inside, and when the volume of the confined space changes from large to small, the hydraulic oil inside is pressed out from the hydraulic zone.
3, plunger pump
The plunger pump has high volume efficiency, small leakage, can work under high pressure, mostly used in high-power hydraulic systems, but the structure is complex, the material and processing accuracy requirements are high, the price is expensive, and the cleanliness of the oil is required.
The plunger pump has a drive shaft, connected with the cylinder, the plunger evenly distributed in the cylinder along the circumference, one end of the plunger is pressed on the fixed swash plate, the other end is equipped with a compression spring between the bottom surface of the pump body, the swash plate relative to the axis of the pump body has an inclination, the piston will always be pressed on the tilting plate. ▼
When the plunger pump works, under the action of the CAM on the camshaft of the injection pump and the plunger spring, the plunger is forced to make up and down reciprocating motion, so as to complete the oil pumping task. The oil pumping process can be divided into two stages: the oil inlet process and the oil return process. The piston on one side of the cylinder block and the sealing volume around the cylinder block gradually increase into the oil absorption area, and the other side gradually decreases into the oil pressure area due to the sealing volume around the cylinder block.
4, gas booster pump
Gas booster
The pneumatic booster pump is mainly driven by low pressure gas at large area piston end to produce high pressure fluid at small area piston end. It can be used to compress air and other gases, and the output pressure can be stepless adjusted by driving pressure.
A variety of gas drives: compressed air, liquefied nitrogen and pipeline nitrogen, water vapor.
【 Hydraulic pump connection precautions 】
1, hydraulic pump can be installed with support or flange, pump and prime mover should use a common base support, flange and foundation should have enough rigidity. Special attention: Piston pumps with a flow rate greater than (or equal to)160L/min should not be installed on the tank.
2, hydraulic pump and prime mover output shaft should be connected by elastic coupling, it is strictly prohibited to install pulley or gear drive hydraulic pump on the hydraulic pump shaft, if you must use pulley or gear and pump connection, you should add a pair of support to install pulley or gear, the support and pump shaft coaxial error should not be greater than Φ0.05mm.
3, the suction pipe should be as short, straight, large and thick as possible, and the suction pipe should generally be set with a crude filter whose nominal flow is not less than 2 times the pump flow (filtration accuracy is generally 80 ~ 180μm). The drain pipe of the hydraulic pump should be directly connected to the tank, and the back pressure of the oil return should not be greater than 0.05MPa. The suction pipe and return pipe of the oil pump should be less than 200mm at the lowest oil level of the oil tank. In particular, the oil filter is not allowed to be installed on the suction pipe of the plunger pump, and the diameter of the stop valve on the suction pipe should be one step larger than the diameter of the oil suction pipe.
4. The inlet and outlet of the hydraulic pump should be firmly installed, and the sealing device should be reliable, otherwise it will cause air inhalation or oil leakage, affecting the performance of the hydraulic pump.
5, the self-priming height of the hydraulic pump does not exceed 500mm(or the inlet vacuum does not exceed 0.03MPa), if the oil supply pump is used, the oil supply pressure shall not exceed 0.5MPa, when the oil supply pressure exceeds 0.5MPa, the pressure sealing ring should be used. For the plunger pump, the self-priming method should be used as far as possible.
6. Before installing the hydraulic pump, check whether the depth of the installation hole is greater than the shaft extension length of the pump to prevent the phenomenon of the top shaft and avoid burning the pump.
【 Hydraulic pump use precautions 】
1, the hydraulic pump should be started several times, after the oil flow direction and sound are normal, run at low pressure for 5 ~ 10min, and then put into normal operation. Before starting the plunger pump, the pump must be filled with clean working oil through the oil drain on the shell.
2, the viscosity of the oil is affected by the temperature and changes, the oil temperature rises and the viscosity decreases, so the oil temperature is required to remain below 60℃, in order to make the hydraulic pump work stably at different working temperatures, the selected oil should have oil temperature characteristics that the viscosity is less affected by temperature changes, as well as better chemical stability, anti-foam performance.
3, the oil must be clean, not mixed with mechanical impurities and corrosive substances, the hydraulic system without filter device on the suction pipe, must be refueled to the tank by the oil filter truck (filtration accuracy is less than 25μm).
4, the highest pressure and the highest speed of the hydraulic pump, refers to the peak value allowed in the short time in use, should avoid long-term use, otherwise it will affect the life of the hydraulic pump.
5, the normal working oil temperature of the hydraulic pump is 15 ~ 65 ° C, the maximum temperature on the pump shell is generally 10 ~ 20 ° C higher than the oil temperature at the pump entrance in the tank, when the oil temperature in the tank reaches 65 ° C, the maximum temperature on the pump shell does not exceed 75 ~ 85 ° C.
[Precautions after replacing the hydraulic pump]
1, always pay attention to the discovery of abnormal phenomena
Abnormal sound, vibration or abnormal signals of the monitoring system must have its cause. When an abnormal phenomenon is found, it is necessary to immediately find the back-and-forth map, find the cause of the anomaly, and evaluate whether it is necessary to stop processing.
2. Do not add the load immediately after the hydraulic pump starts
The hydraulic pump must be implemented for a period of time without load idling (about 10 minutes to 30 minutes) after starting, especially when the temperature is very low, it is more necessary to warm the process, so that the hydraulic circuit circulation is normal and then add the load, and confirm the operation status.
3, observe the oil temperature change
Pay attention to check the maximum and minimum oil temperature changes and the relationship between the oil temperature and the external environment temperature, and determine whether the capacity of the cooler and the capacity of the oil storage tank are compatible with the surrounding conditions and the use conditions to ensure that the troubleshooting of the cooling system is tracable.
4, pay attention to the noise of the hydraulic pump
The new hydraulic pump has less initial wear, is susceptible to the impact of bubbles and dust, poor lubrication at high temperatures or overload conditions, etc., will cause adverse consequences, so that the hydraulic pump sends out abnormal effects.
5, pay attention to check the display value of the meter class
Observe the pressure gauge display value of the hydraulic circuit at any time, and the vibration stability of the pressure switch signal light to find out whether the hydraulic circuit is normal as soon as possible.
6, pay attention to the adjustment of each valve
Fully understand the use of pressure control valves, flow control valves and direction control valves, and pay special attention to the adjustment range and limit, otherwise the adjustment error will not only damage the machinery, but also pose a threat to safety.
7. Check the status of the filter
The filter in the loop should be taken out and cleaned regularly, and the state of the filter and the adsorbent dirt should be checked, the quality, amount and size should be analyzed, the loop situation should be known, and the source of pollution should be clear.
8. Check the change of hydraulic oil regularly
Check and analyze the deterioration, discoloration and pollution degree of hydraulic oil every 1 to 2 months to ensure the normal operation of hydraulic transmission media.
9, pay attention to the leakage of the piping part
Whether the piping of the hydraulic device is good can be seen after running for a period of time, check whether there is oil leakage and whether the piping is loose.
10, the new machine should pay attention to the operation of the three months
During the operation of the new machine, the operation condition should be checked, such as the maintenance of the parts, whether the screws are loose, whether the oil temperature is abnormal, whether the hydraulic oil is soon deteriorated, and whether the conditions of use are in line with the regulations.
11. Cause of mechanical loss
1. When the hydraulic pump works, there is mechanical friction between the relative moving parts, such as between the bearing and the shaft, between the shaft and the seal, and between the blade and the pump body wall, resulting in friction resistance loss. This loss is related to the output pressure of the hydraulic pump, and the higher the output pressure, the greater the friction resistance loss.
2. When the oil flows in the pump, the viscous resistance due to the viscosity of the liquid will also cause mechanical loss. This loss is related to the viscosity of the oil and the speed of the pump, the more viscous the oil and the higher the speed of the pump, the greater the mechanical loss.
Due to the above reasons, the actual input power of the pump is greater than the theoretically required power. The ratio of the theoretical input power to the actual input power of the hydraulic pump is called the mechanical efficiency, which indicates the degree of power loss. The ratio of the output power to the input power of the hydraulic pump is called the total efficiency of the hydraulic pump.
12. Causes of volume loss
1. Although the suction chamber and the discharge chamber of the positive displacement hydraulic pump are separated in the pump, there is always a certain gap in the relative movement, so the oil in the high pressure area of the pump must leak into the low pressure area through the gap. The lower the viscosity of hydraulic oil and the higher the pressure, the greater the leakage.
2. Hydraulic pump in the oil suction process, due to the oil suction resistance is too large, the oil is too sticky or the pump shaft speed is too high, will cause the suction phenomenon of the pump, so that the working volume of the seal can not be filled with oil, that is to say, the working chamber of the hydraulic pump is not fully utilized.
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