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Common sense of vacuum
1, the definition of vacuum Vacuum system refers to the lower than the atmospheric pressure of rare books gas state 2, the degree of vacuum in the vacuum under the thin gas level, usually with "high vacuum" and "low vacuum" to represent. High degree of vacuum means that the degree of vacuum "good", low degree of vacuum means the degree of vacuum "bad." 3, the vacuum unit is usually Torr unit, in recent years the international access to Pa (Pa) as a unit. 1Torr = 1 / 760Atmospheric pressure = 1 mmHg 4, care and the conversion of 1 Pa = 133.322 Pa or 1 Pa = 7.5 × 10-3 Torr 5, the average free path for the rule of motionless thermal particles of gas, followed by two The average distance traveled by a collision is indicated by the symbol "λ". 6, the flow rate per unit time through the gas cross-section of any amount, the symbol "Q" that the unit is Pa · L / s or Torr · L / s. 7, Flow Chart Indicates the ability of a vacuum line to pass gas. The unit is liters per second (L / s). At steady state, the duct conductance is equal to the duct flow divided by the pressure difference across the duct. The symbol is marked as "U". U = Q / (P2-P1) 8, pressure or pressure gas molecules acting on the container wall unit force, with "P" said. 9, the standard atmospheric pressure pressure per square centimeter of 101,325 daints, symbol: (Atm). 10, the ultimate vacuum After the full vacuum pump evacuated, stable at a certain degree of vacuum, the vacuum is called the ultimate vacuum. Usually vacuum container after 12 hours refining, and then after 12 hours of vacuum, the last hour measured every 10 minutes, whichever is the average of 10 times the ultimate vacuum value. 11, pumping rate at a certain pressure and temperature, the unit of time taken from the pump inlet gas pumping speed, referred to as the pumping speed. Namely Sp = Q / (P-P0) 12, the thermocouple vacuum gauge thermocouple potential and the temperature of the heating element, the element temperature and the heat transfer of gas related to the principle of measuring the degree of vacuum gauges. 13, ionization vacuum gauge (also received hot cathode ionization gauge) by the cylindrical collector, grid and located in the center of the grid filament composition, tubular collector pole outside the grid. The hot cathode emits electrons to ionize the gas molecules, the ions are collected at the collector, and the gas gauge measures the gas pressure based on the size of the collected ions. 14, the composite vacuum gauge by the thermocouple gauge and hot cathode ionization gauge, measuring range from the atmosphere ~ 10-5Pa. 15, cold cathode ionization at both ends of the anode tube has a pair of cathode plate, the role of an external magnetic field, the anode tube to form Penning discharge generated ions, according to the size of the cathode plate collected ion flow to determine the gas pressure gauge. 16, the resistance of the vacuum gauge using the resistance of the heating element and the temperature, the temperature of the element with the principle of gas conduction through the bridge circuit to measure the degree of vacuum gauge. 17, McLaren vacuum gauge (compression vacuum gauge) The gas to be tested with mercury (or oil) compressed to a very small volume, and then compare open tube and closed tube liquid column difference, the use of Boyle's law directly calculate the gas An absolute vacuum gauge. 18, B-A This is a cathode and collector inversion of the hot cathode ionization gauge. The collector is a filament placed in the center of the grid, with the filament placed outside the grid, thus reducing soft X-ray effects and extending the lower limit of measurement for ultra-high vacuum. 19, water ring vacuum pump impeller rotor rotation and produce water ring. As the rotor eccentric rotation and the water ring and the blade between the cyclical changes occurred during the mechanical vacuum pump suction. 20, the reciprocating vacuum pump piston reciprocating motion and the mechanical vacuum pump. 21, oil seal Mechanical vacuum pump oil to keep the seal of the mechanical vacuum pump, can be divided into fixed-chip, rotary chip, slide valve type, trochoidal line type. 22, Roots vacuum pump with a pair of synchronous high-speed rotation of the shoe-shaped rotor mechanical vacuum pump, the pump can not be a separate suction, front-level need to be equipped with oil seals, water rings and other can be directly to the atmosphere of the vacuum pump. 23, Turbomolecular vacuum pump has a high-speed rotation of the impeller, when the gas molecules and high-speed rotation of the turbine blades were driven to the outlet before being removed by the foreline pump. 24, the oil diffusion diffusion pump vacuum pump nozzle jet high-speed steam flow. In the molecular flow conditions, the gas molecules continue to spread to the steam flow, and the steam to the pump outlet by the compression stage by stage before the exclusion of the pump. 25, low-temperature vacuum pump 20K below the surface of the condensing gas adsorption vacuum pump. 26, cold trap (water-cooled baffle) placed between the vacuum vessel and the pump, for adsorption of gas or oil vapor capture device. 27, the gas valve seal Mechanical vacuum pump to open a small hole in the compression chamber, and fitted with regulating valve, when the valve is opened and adjust the amount of air into the rotor to a certain position, the air through this hole into the compression chamber to reduce compression Ratio, so that most of the steam does not cause condensation and the gas is mixed with the exclusion of the role of the pump valve is called the gas valve. 28, vacuum freeze-drying Vacuum freeze-drying, also known as sublimation drying. The principle is to freeze the material so that the water it contains becomes ice and the ice sublimes under vacuum to achieve the purpose of drying. 29, vacuum evaporation In a vacuum environment, the material is heated and plated onto the substrate known as vacuum evaporation, or vacuum coating. 30, vacuum drying Vacuum characteristics of the lower boiling point to dry items method. 31, the common name of the vacuum system (1) the main pump: In the vacuum system, to obtain the required degree of vacuum to meet the specific requirements of the vacuum pump, such as vacuum coating machine oil diffusion pump is the main pump. (2) Foreline Pumps: A vacuum pump used to maintain the pressure at the foreline of a vacuum pump below its critical foreline pressure. Such as the Roots pump configuration before the rotary or slide valve pump is the foreline pump. (3) Roughing Pump: A vacuum pump that starts pumping at atmospheric pressure and pumps the system pressure to another vacuum pump. Such as vacuum coating machine in the valve pump, is the crude oil pump. (4) to maintain the pump: In a vacuum system, when the gas is small, can not effectively use the foreline pump. To this end configure a smaller auxiliary pump to maintain the main pump work, this pump is called to maintain the pump. If diffusion pump outlet with a small rotary vane pump, is to maintain the pump.