Water ring vacuum pump with air eject
1. The structure and working principle of water ring vacuum.
The pump body and its two sides of the front distribution gas disk, the rear gas plate to form a cavity. The impeller is placed in the cavity, and its axis is parallel to the pump body axis and has certain eccentricity. Suction and vent holes are opened on the front and rear distribution disks.
A certain amount of working water is injected into the pump before starting the pump, and the water quantity is controlled by the automatic discharge valve. Due to the lower part of impeller blades in the water, when the impeller rotates, the blade will drive the water movement, the effect of the centrifugal force to form a water tight stick the rotation of the shell wall water ring, the axis of the water ring basic coaxial line, with the pump body and inner surface and wheel hub surface and water ring on both sides of the cover face formed between a crescent-shaped work space, the space can be separated by blade into a chamber, the chamber volume with the impeller rotating constantly change.
The impeller turns clockwise, and in the first half, the volume of the working small cavity is formed from small to large. Thus, the external gas enters the working chamber through the suction chamber of the air inlet and the rear pump cover. In the second half, the small cavity volume of the working chamber is smaller, the gas is compressed, the pressure is increased, and the exhaust outlet of the gas distribution plate is discharged.
2. Damage situation and solution of vacuum pump impeller.
By vacuum pump for overhauling, detailed observations of vacuum pump damage: a piece of falling leaves, leaf appear rupture, reinforcement ring and blade joints have a fracture phenomenon, pump body damage, distribution board has scratches, states that this is typical of the vacuum pump running the damage caused by blade fatigue fracture.
2. Analysis of causes of cavitation erosion in vacuum pump impeller.
Vacuum pump cavitation is a physical phenomenon, when under certain temperature and vacuum, the cavitation will occur, due to the unit the rigor of uncertainty, the general design selection and vacuum pump selection will have a larger margin, so when the unit less rigor also can meet the design requirements. But when the unit has a good precision, vacuum pump and has a certain margin, in this way, the condenser vacuum is higher, although it's good for power generation efficiency of the unit, but inevitably face the influence of cavitation vacuum pump. The increase of the working water temperature reduces the performance of the pumping equipment and has a negative effect on the condenser vacuum.
Single stage vacuum pump is more compressed than large, especially sensitive to working water temperature. When the working water temperature rises, the impeller is damaged by cavitation. Preventing cavitation damage to vacuum pump is a key technology. The reasons for the damage of the vacuum pump impeller are analyzed in the following aspects:
(1) vacuum pump selection is too large, resulting in cavitation of vacuum pump, which can not meet the work needs.
(2) the working environment and working conditions change, and the actual working conditions are not in accordance with the design conditions, so that the vacuum pump can produce cavitation. The condenser air tightness is good, the vacuum degree of the system is high. Thus, the vacuum pump operates in the limit state, and the cavitation phenomenon occurs.
(3) the heat exchange effect of the heat exchanger has great influence on the performance of the pump. The cooling water temperature is high, the heat exchange effect of the heat exchanger is poor, and the temperature of the cooling liquid causes the cavitation of the pump.
(4) the design of vacuum pump is not reasonable, the effective cavitation residual is insufficient, and the vacuum pump produces cavitation.
2. Solution of vane cavitation in vacuum pump.
From the above analysis on the cause of the vacuum pump impeller cavitation occurred, if you want to be fundamentally solved vacuum pump cavitation problem, one is to reduce the cooling water temperature, but the cost is very big, 2 it is to reduce the degree of vacuum, also is to let the condenser back pressure rise, this way is less feasible, it will seriously affect the loading capacity of generating unit and the unit of economy, the ideal way is in the original water temperature under the condition of invariable, condenser vacuum cavitation, can completely solve the best way is to vacuum pump equipped with air injector, so that we can change the extraction of vacuum pump performance, And condenser vacuum can still guarantee before modification level or higher, so the water ring - spray vacuum pump unit can effectively avoid the generation of cavitation, because when the condenser vacuum in 3 ~ 5 kpa, the first level of water ring - spray vacuum pump unit (spray) suction pressure is 3 ~ 5 kpa, but as a secondary vacuum pump suction pressure at about 12 kpa, in this way, the same working temperature, no possible cavitation phenomenon, completely solve the causes of cavitation, and when the rigor of unit is better, Water ring - a jet pump can achieve a higher vacuum than a single vacuum pump.
3. The principle of the atmospheric jet pump.
As a mature product, water ring jet pump has been widely used in various industries, and it is also widely used as a vacuum equipment for the extraction of condenser. The complete set of injector equipped with water ring vacuum pump is designed for the performance of the vacuum pump, which can achieve the optimum efficiency. Compared to a single vacuum pump, the condenser vacuum may be higher. Air ejector is also known as atmospheric injection vacuum pump, which can be used as medium in atmospheric atmosphere directly.
Air ejector function is the use of atmospheric pressure differential pressure relative to the vacuum pump, air jet, in the injector lower than the vacuum pump for suction pressure, thereby eliminating the limit of the vacuum pump pressure, prevent vacuum pump cavitation, protect the vacuum pump. When the compressed air enters the minimum section of the throat of the laval nozzle, the pressure reaches the critical value PK, where the air velocity reaches the speed of sound VK. In the expansion section of the laval nozzle, the speed gradually rises and the pressure continues to drop. When the nozzle exit is reached, the speed is supersonic and the pressure is P/0. After the compressed air flows out of the nozzle, it continues to expand to P//0. The pressure of the compressed air is the same as the pressure of the pumped gas, which is P/0=P//0. The pressure difference of the pumped gas from P1 to P//1 makes the pumped gas significantly accelerate. Compressed air and gas is pumped two strands in mixed indoor airflow mutual blending of momentum and energy exchange, the compressed air by pressure can change the kinetic energy to be smoke gas, thus reduce speed where V0 gradually compressed air is pumped gas velocity V1 increased gradually, gradually close to the speed. Finally, somewhere in the diffuser throat department both speed to achieve consistently V / 3, and produce a shock wave, the mixing air velocity drops, from before the shock wave of supersonic fell to subsonic V3, after the shock wave pressure rise at the same time to P3.
In practical application, the air injection pump is used as a water ring for the front stage pump of the water ring pump, to improve the limit pressure of the water ring pump and expand its working range. Since the water ring pump is limited by the water temperature, the exhaust gas rate of the water ring is greatly reduced and the cavitation is easily generated inside the water ring pump, which is very beneficial to the air injection pump. Cavitation is a physical phenomenon, when the high vacuum to a certain value, the water inside the vacuum pump can produce bubbles burst phenomenon, do not break when appear this kind of phenomenon will cause a vacuum pump noise increased, appear this kind of circumstance is not the quality problem of the pump, as long as it is water as working liquid in the vacuum pump will appear this kind of situation; However, the cavitation phenomenon is an abnormal condition for the vacuum pump, which often affects the service life of the vacuum pump. The best way to avoid running in this situation is to pump the vacuum pump with an atmospheric jet pump. After add the atmospheric jet pump, when the generator set runs during the winter, the whole vacuum pump suction performance is increased, so the condenser vacuum pump can be guaranteed in the current level or higher, but its internal vacuum around 12 kpa vacuum pump ontology so that it effectively avoid the generation of cavitation.
When starting the water ring pump, the pressure difference between the nozzle inlet and the exhaust outlet is formed, and the air is put into the pump. Half of the pressure difference of air pressure, air medium by the accelerated for nozzle contraction, can achieve sound speed to the throat, to expand further speed up to the supersonic, toward the diffuser, high-speed jet formation, and inhaling indoor pressure is lower than by pumping the pressure inside the container, so will be inhaling indoor smoke gas. Due to the mixing of the two air currents in the inhalation chamber, the loss caused by the momentum exchange slows down the airflow velocity, and then falls below the sound speed when entering the throat of the diffuser. The diffuser expansion period, further reduce the speed, pressure rising, the last is atmospheric jet pump exhaust pressure, the water ring pump suction pressure, by water ring pump the gas suction, and then discharge pump, the suction, exhaust process is completed.