1.1 Water ring vacuum pump system introduction and process flow diagram
Water ring vacuum pump is a common equipment of vacuum pump system. The water ring vacuum pump used in a device provides a certain vacuum (absolute pressure: 66 ~ 77 kPa) for the production process. The schematic diagram of the process is shown in Figure 1: The pump traps the air trap The air medium is sucked out to form a vacuum for use in the production process; the exhaust gas is discharged to the gas-liquid separator. The pump model: 2BE1253-0, speed: 740 rpm, power: 75 kW; medium: water, air, small amount of material.
1.2 Principle of water ring vacuum pump
The working principle of the water ring vacuum pump system is shown in Figure 2. The impeller 1 is eccentrically mounted in the pump body, and many impellers are mounted on the impeller. Before starting the water ring pump, a certain amount of water is injected into the pump. When the impeller reaches a certain speed, the water in the pump is stirred by the blades, and it is thrown to the surrounding shell wall under the action of centrifugal force to form a water ring with a certain thickness. The upper inner surface of the water ring is in contact with the impeller hub 2. When the impeller rotates clockwise, during the first half of the rotation, the inner surface of the water ring gradually disengages from the hub, and the cavity formed between adjacent blades gradually increases. Large, the pumped gas passes through the pump intake pipe, and is continuously sucked into the cavity through the crescent-shaped suction hole; during the second half of the rotation, the inner surface of the water ring gradually approaches the hub, and the cavity between two adjacent blades gradually decreases. The gas is compressed. When the pressure is increased to be higher than the external pressure, the gas is discharged, so that the gas is continuously pumped away to form a certain vacuum.
2 Application Technology Analysis
2.1 Failure phenomenon caused by excessive or insufficient working fluid
A continuous supply of make-up water is essential when the pump is running. The main effect of make-up water on the water ring pump is: the compression heat generated by the compressed gas is discharged; the loss of the make-up water ring with the gas flowing out of the exhaust hole; cooling the mechanical seal and other parts. During work, too much or too little working fluid will have a bad effect on the pump's work.
(1) The degree of vacuum decreases. Insufficient water supply directly affects the formation of the liquid ring in the pump body. A closed cavity cannot be created between the two blades of the impeller, and there is no change in the size of the cavity to form a vacuum.
(2) Pump body vibration or shaft power increase. If the inner diameter of the water ring becomes larger due to insufficient water supply, the tip of the blade will collide with the inner wall of the water ring to generate vibration; if the inner diameter of the water ring becomes smaller (due to excessive water supply), the disturbance and resistance loss of the impeller will increase, causing vibration, and at the same time Increasing the power consumption of the pump leads to an increase in shaft power;
In order to maintain an appropriate amount of water, valves and water meters must be installed on the water inlet pipeline. When insufficient or excessive water is found, the water should be replenished in a timely manner. Table 1 shows the relationship between different suction pressures and the amount of water supplemented.
2.2 Fractured valve
The water ring vacuum pump system is equipped with a valve disc next to each of the two exhaust port distributors, which is used to eliminate the over-compression or under-compression that may occur during the vacuum pump operation, and to avoid the increase of the power consumption and the decrease of the efficiency of the pump. The valve plate can move in the axial small distance between the distributor and the baffle.
When the pressure of the compressed gas in the pump is less than the pressure at the pump outlet, the valve disc moves toward the impeller and is closely attached to the distributor, preventing the air at the pump outlet from entering the small cavity to ensure that the gas continues to be compressed. When the pressure is greater than the pump outlet pressure, the gas punches through the exhaust port to open the valve disc, so that the upper part of the valve disc swings at an angle so that the gas can be smoothly discharged. In this way, the lower part of the valve disc is often closely attached to the distributor, and the upper part is swung at an angle, which is twisted into an "S" shape. Long-term distortion causes the stress concentration in the middle of the valve disc, which causes fatigue damage and breaks from the middle. After the valve disc is broken, it has the following effects:
(1) The bearing heats up. When a valve disc breaks, the pressure on both sides of the impeller will be unbalanced, and the rotor will generate axial force, which will increase the load on the ball bearing. Long-term operation will cause the bearing temperature to rise. When both valve discs are broken, the locations of the fractures are not exactly the same, and the pressure on both sides of the impeller is also slightly unbalanced. The axial force will be reduced compared to when a valve disc is broken, and the bearing temperature will decrease, but still Higher.
(2) The shaft power increases, the valve disc cannot achieve proper coverage of the distributor in the correct state, and some of the exhausted gas will flow back into the working cavity, and it will be repeatedly compressed and discharged, causing energy loss and increasing the motor load. .
(3) The degree of vacuum drops. When both sides of the valve disc are broken, the vacuum of the vacuum pump system will drop sharply. After the valve disc is broken, it must be replaced in time. If one valve disc is not replaced in time, the service life of the other valve disc will be greatly shortened, and it will also break in a short period of time.
2.3 Pump body vibration or abnormal noise
The normal vibration of the water ring vacuum pump system is caused by the water ring vortex. When the pump body vibrates too much, if the foundation and the base are not vibrating, the vibration caused by the loose anchor bolts can be ruled out. The main reason is the pump body itself. .
(1) The rubber pad of the coupling is damaged: The rubber cushion is easy to wear and even be ground into powder and thrown out, which causes the two pairs of wheel pairs of the coupling to directly rub and aggravate the rotor vibration. Use good quality cushions at work and check for wear regularly.
(2) Operation under extreme vacuum: The cavitation phenomenon generated in the pump will cause the pump body to vibrate and noise, and will cause severe damage to the parts inside the pump. Inflating the air inlet of the pump can effectively prevent the cavitation damage caused by the pump running under the extreme vacuum.
(3) If the bearing is damaged or the bearings on both sides are misaligned, check it in time, replace the bearing or adjust the bearing.
2.4 Bearing overheating
The bearing should have good working conditions. Its operating temperature should not exceed the ambient temperature of 35 to 40 ° C, but the maximum temperature (regardless of the ambient temperature) must not exceed 75 ° C. The main causes of bearing heating are as follows:
(1) Shaft end seal failure: When the shaft end seal is damaged, air will be sucked into the pump, affecting the suction and exhaust performance of the pump. If the one-sided seal fails, the pressure on both sides of the impeller will be unbalanced, the rotor will generate axial force, and the ball bearing will be heated due to the increased load.
(2) Excessive pre-tension of the bearing: The adjustment of the pre-tension should not be overdone, otherwise the bearing clearance will be reduced or no clearance, and it will easily cause the bearing to heat up.
(3) Improper lubrication: Too much or too little grease added, mismatched grease types, long-term deterioration of grease use, and grease contamination can cause bearing heating.
2.5 Reduced inspiratory capacity or vacuum
There are two main reasons for this phenomenon: the pump itself is malfunctioning or gas is leaking due to poor sealing of the piping system. Figure 3 is the performance curve of the suction rate and suction pressure.
(1) Vacuum leakage: There are two main aspects: leaks in the piping system and leaks in the mechanical seal: the leaks in the piping system are not good and gas is leaked. You can find out the leaks and eliminate the leaks by conducting pressure tests on the pipeline ; Mechanical seal leaks, when the shaft end seal is damaged, air will be sucked into the pump through the gap between the mechanical seal and the shaft sleeve, affecting the suction performance of the pump, resulting in a decrease in vacuum;
(2) Water ring heating: Excessively high water temperature will cause water to vaporize and evaporate, and negative pressure conditions will further exacerbate the occurrence of vaporization and evaporation, causing excessive water vapor in the pump body. In this way, the pump draws too much water vapor when inhaling, and rarely inhales the air, resulting in a low vacuum of the vacuum pump system. Measures to prevent the water temperature from becoming too high: reduce the temperature of the water supply; keep the water inlet and outlet channels unobstructed; adjust from the process to reduce the temperature of the host material as much as possible to reduce the suction temperature of the vacuum pump
(3) Bearing skew: This phenomenon causes the impeller to be tilted into the pump body, resulting in uneven axial clearance. When the impeller rotates, a part of it will inevitably rub against the side cover, scratch the side cover and the end face of the impeller, and increase the axial clearance. When the compression chamber gas passes through the enlarged gap, it leaks into the suction chamber in large quantities, which reduces the vacuum degree or the exhaust pressure. At this time, the bearing must be removed for repair, and then installed correctly.
The pump: pumping speed 35 m 3 / min, speed 740 r / min, under specific conditions of use, suction pressure (absolute pressure): about 54 kPa, vacuum (absolute pressure): about 47.3 kPa, which meets 66 ~ 77 kPa usage requirement.
Note: The performance shown in Figures 3 and 4 is based on the conditions of intake air temperature of 20 ℃, inlet water temperature of 15 ℃, and exhaust pressure of 101.3 kPa. The gas being sucked in is saturated steam; the performance tolerance is ± 10%.
2.6 shaft power increase
There are several main reasons for the increase in shaft power (the value displayed by the ammeter is too large). Figure 4 shows the performance curve of shaft power and suction pressure.
(1) The gap between the impeller and the distribution plate is too small, and it is easy to rub after being heated; increase the thickness of the spacer between the distribution plate and the impeller, and adjust to a suitable gap to effectively prevent friction; ; Check in time, replace the bearing or adjust the bearing.
(3) Fouling in the pump: After the fouling of the distribution plate, the area of the suction and exhaust ports of the pump changes, and the local loss of the airway increases due to deviations from the design conditions; after the pump casing fouls and rusts, the resistance of the water ring along the path As the coefficient increases, the loss increases. The superposition of various losses increases the working load of the motor. Fouling of components requires regular inspection and timely cleaning: scales and impurities deposited in the exhaust channel; after each stop or pickling, drain water, acid and dirt in the channel.
In order to maintain the normal operation of the water ring vacuum pump system, it should be frequently observed whether the vacuum degree, exhaust pressure and shaft power are normal and stable, and the amount of water and water and the sound of the pump running are normal. , Can find problems in time, take corresponding treatment and repair measures to ensure its stable operation; at the same time, strengthen the maintenance and repair work after the pump is shut down, so that the pump is in a good standby state; various faults of the water ring vacuum pump system are interconnected Yes, each failure phenomenon involves many factors. In the specific treatment, specific measures must be taken according to the daily use of the equipment and the specific status of the failure.
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