Addtime： 2020-07-17 Browse times： 2020
Vacuum pump is a kind of device to maintain vacuum by pumping air from the container under the action of electromagnetic force. Vacuum pump is usually widely used in low temperature equipment, papermaking machinery, vacuum equipment, petroleum, mining, foundation treatment and other fields. Different vacuum pumps have different working principles and uses. Today I would like to share with you the working principle and maintenance tips of several common vacuum pumps.
1、 Water ring vacuum pump
The eccentric rotor with fixed blades in the pump throws water to the stator wall, forming a liquid ring concentric with the stator. The liquid ring and the rotor blade together constitute a variable volume rotary variable volume vacuum pump. The rotating vane is divided into single-stage and double-stage. The principle is that the eccentric rotor is used to form in the pump cavity, and the gas is discharged from the pump through the change of the volume generated by rotation. The main reason is that during the suction process, the volume of the suction chamber increases and the vacuum degree decreases, so the gas in the container is sucked into the pump cavity. During the exhaust process, the volume becomes smaller and the pressure increases, and finally the gas is discharged from the pump through the oil seal.
2、 Roots vacuum pump
In the pump cavity of roots pump, there are two "8" shaped rotors installed vertically on a pair of parallel shafts, and a pair of gear belts with transmission ratio of 1 act in the opposite synchronous rotation motion. There is a certain gap between the rotors and the inner wall of the pump shell, which can realize high speed operation. Because roots pump is a kind of vacuum pump without internal compression, the compression ratio is usually very low, so the high and medium vacuum pumps need the front stage pump. The limit vacuum of roots pump depends not only on the structure and manufacturing accuracy of the pump itself, but also on the limit vacuum of the previous stage pump.
In order to improve the limit vacuum degree of the pump, roots pump can be used in series. The working principle of roots pump is similar to roots blower. Due to the continuous rotation of the rotor, the extracted gas is drawn into the space V0 between the rotor and the pump shell from the air inlet, and then discharged through the exhaust port. Because the V0 space is completely closed after suction, there is no compression and expansion in the pump chamber. However, when the top of the rotor turns around the edge of the exhaust port and the V0 space is connected with the exhaust side, a part of the gas will recoil into the space V0 due to the high gas pressure on the exhaust side, which makes the gas pressure suddenly increase. When the rotor continues to rotate, the gas is discharged from the pump.
3、 Rotary vane vacuum pump
Rotary vane vacuum pump is a kind of mechanical vacuum pump with oil seal. Its working pressure range is 101325 ~ 1.33 × 10-2 (PA), which belongs to low vacuum pump. It can be used alone, and can also be used as the front stage pump of other high vacuum pumps or ultra-high vacuum pumps. The rotary vane pump can pump out the dry gas in the sealed container, and a certain amount of condensable gas can also be pumped out if there is a gas stabilizer. However, it is not suitable for the removal of gases with high oxygen content, corrosive to metal, chemical reaction to pump oil and dust particles. Rotary vane pump is one of the most basic vacuum equipment in vacuum technology. Rotary vane pump is mostly small and medium-sized pump.
Rotary vane pump has single-stage and two-stage. The so-called two-stage, is in the structure of two single-stage pumps in series. Generally, it is made of two stages to obtain higher vacuum. The relationship between the pumping speed and the inlet pressure of the vane pump is specified as follows: when the inlet pressure is 1333pa, 1.33pa and 1.33 × 10-1 (PA), the pumping speed value shall not be lower than 95%, 50% and 20% of the nominal pumping speed of the pump respectively. Rotary vane pump is mainly composed of pump body, rotor, rotating blade, end cover, spring, etc. A rotor is eccentrically installed in the cavity of the vane pump. The outer circle of the rotor is tangent to the surface of the pump cavity (there is a small gap between them). Two rotors with springs are installed in the rotor groove. When rotating, centrifugal force and spring tension keep the top of the vane in contact with the inner wall of the pump chamber, and the rotating rotor drives the vane to slide along the inner wall of the pump chamber.
The crescent shaped space surrounded by the rotor, pump chamber and two end covers is divided into three parts a, B and C by two rotating blades. When the rotor rotates in the direction of arrow, the volume of space a connected with the suction port is gradually increased and is in the process of suction. The volume of space C connected with the exhaust port is gradually reduced and is in the process of exhaust. The volume of space B in the middle is also gradually decreasing and is in the process of compression. As the volume of space a is gradually increasing (that is, expansion), the gas pressure is reduced, and the external gas pressure at the pump inlet is greater than that in space a, so the gas is inhaled. When space a is isolated from the suction port, i.e. to the position of space B, the gas begins to be compressed, the volume gradually reduces, and finally communicates with the exhaust port. When the compressed gas exceeds the exhaust pressure, the exhaust valve is pushed open by the compressed gas, and the gas is discharged into the atmosphere through the oil layer in the oil tank. By the continuous operation of the pump, the purpose of continuous pumping is achieved. If the discharged gas is transferred to another stage (low vacuum stage) through the airway, it is pumped out by the low vacuum stage, and then compressed by the low vacuum stage and discharged into the atmosphere, which is a two-stage pump. In this case, the total compression ratio is borne by two stages, thus increasing the limit vacuum degree.
How much do you know about the maintenance of vacuum pump? Now I will reveal some maintenance tips for you.
1. Check the oil level frequently. If it does not meet the requirements, it must be adjusted to meet the requirements. When the vacuum pump is running, the oil level to the center of the oil mark shall prevail.
2. The oil change period shall be considered according to the actual service conditions and whether it can meet the performance requirements, etc., and is determined by the user at his discretion. General new vacuum pump, when pumping clean and dry gas, it is recommended to change oil once every 100 hours. After the black metal powder is not seen in the oil, the oil change period can be appropriately extended in the future.
3. Check the oil quality regularly and replace the new oil in time in case of oil deterioration to ensure the normal operation of vacuum pump.
4. Vacuum pump in the first month of operation, after 100 hours of oil change, after every 500 hours, change oil once.
5. In general, the vacuum pump should be overhauled after 2000 hours of operation. Check the aging degree of rubber seal, check whether the exhaust valve plate is cracked, and clean the dirt deposited on the valve plate and exhaust valve seat. Clean the whole vacuum pump cavity parts, such as rotor, rotor, spring, etc. It is usually cleaned with gasoline and dried. After cleaning rubber parts, dry them with dry cloth. When cleaning and assembling, handle with care to avoid bumping.
6. Add the bearing lubricating oil into the bearing body, observe that the oil level should be at the center line of the oil mark, and the lubricating oil should be replaced or supplemented in time.
7. Check the vacuum pump pipeline and joint for looseness. Turn the vacuum pump by hand to see if it is flexible.
8. After the re assembly, it should be put into trial operation. Generally, it is necessary to run for 2 hours without load and change the oil twice. Because there will be a certain amount of volatile matter left in the vacuum pump during cleaning, it can be put into normal operation after the operation is normal.
9. Start the motor. After the vacuum pump runs normally, open the outlet pressure gauge and the inlet vacuum pump. Gradually open the gate valve and check the load of the motor after it shows the appropriate pressure.
10. The flow and head of the vacuum pump should be controlled within the range indicated on the label as far as possible, so as to ensure that the vacuum pump operates at the highest efficiency point, so as to obtain the maximum energy-saving effect.
11. To stop using the vacuum pump, first close the gate valve, pressure gauge, and then stop the motor.
12. During the operation of vacuum pump, the bearing temperature should not exceed 350C and the maximum temperature should not exceed 800C.
13. Vacuum pump in the first month of operation, after 100 hours of oil change, after every 500 hours, change oil once.
14. The packing gland should be adjusted regularly to ensure that the leakage in the packing chamber is normal. Regularly check the wear of the shaft sleeve, and replace it in time if the wear is large.
15. If the vacuum pump is out of service for a long time, all the pumps should be disassembled, the water should be wiped dry, the rotating parts and joints should be coated with grease, and properly kept. When vacuum pump is used in cold winter season, after shutdown, it is necessary to screw off the drain plug at the lower part of the pump body to drain the medium completely to prevent frost cracking.
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