Vacuum pump structure features

First, the overall structure of the pump:

The layout of the pump body of the vacuum pump determines the overall structure of the pump. The horizontal structure of the inlet and outlet openings of the vertical structure makes it easier to assemble and connect the piping. However, the center of gravity of the pump is high, and its stability is poor at high speeds, so this type is mostly used for small pumps. The inlet of the horizontal pump is at the top and the exhaust port is at the bottom. Sometimes it is convenient to install and connect the vacuum system piping. The exhaust port can be taken out from the horizontal direction, that is, the inlet and exhaust directions are perpendicular to each other. At this time, the exhaust port can be opened in either left or right direction except for one end of the exhaust pipe, and the other end is blocked or connected to the bypass valve. This type of pump has a low center of gravity and good stability at high speeds. Generally large and medium-sized pumps use this structure. The two rotor shafts of the pump are mounted perpendicular to the horizontal plane. This kind of structural assembly clearance is easy to control, the rotor assembly is convenient, and the pump has a small footprint. However, the higher the center of gravity of the pump and the inconvenience of disassembling the gear, the lubrication mechanism is also relatively complicated.

Second, the pump drive mode:

The two rotors of the vacuum pump are relatively synchronously operated by a pair of high-precision gears. The drive shaft is coupled to the motor via a coupling. There are mainly two kinds of transmission structure layouts. One is that the motor and gear are placed on the same side of the rotor as shown in the figure. The driven rotor is directly driven by the motor end gear, so that the torsional deformation of the active rotor shaft is small, the gap between the two rotors is not changed due to large torsional deformation of the drive shaft, so that the gap between the rotors is running. Uniform in the process.

The biggest disadvantages of this transmission method are: a. There are three bearings on the drive shaft, which increases the difficulty of processing and assembly of the pump, and the disassembly and adjustment of the gears is inconvenient; b. The overall structure is uneven, and the center of gravity of the pump is biased toward the motor and gears. Side of the box.

The quality of a vacuum pump depends on its mechanical structure and the quality of the oil. It must be protected when using a vacuum pump. If the volatile organic solvent is distilled, the organic solvent will increase the vapor pressure by the oil absorption, which will reduce the evacuation efficiency. If it is an acid gas, it will corrode the oil pump. If it is water vapor, it will make the oil into milk. The turbid fluid evacuated the vacuum pump.

Therefore when using a vacuum pump, the following points must be observed:

1. An absorption device must be installed between the distillation system and the vacuum pump.

2. The vapor of the organic solvent in the system must be thoroughly pumped off before distillation.

3, if you can use the pump pumping, try to use a pump, such as distillation of volatile substances contained in the material, can be pumped down with a pump, then switch to the oil pump.

4. The decompression system must be kept air-tight, all rubber plugs should be of the correct size and hole, and rubber hoses should be used for the vacuum hoses. Ground glass coated with vacuum grease.

Depending on the scope of use and pumping efficiency, vacuum pumps can be divided into three categories:

  (1) General pumps, pressure can reach 1.333 ~ 100kPa (10 ~ 760mmHg) as " coarse " vacuum.

  (2) The oil pump, pressure up to 0.133~133.3Pa (0.001~1mmHg) is the " second highest " vacuum.

   (3) Diffusion pump, the pressure can reach 0.133Pa or less, ( 10-3mmHg ) as " high " vacuum.

For lower pressures, use an oil pump that can pump 133.3 Pa (1 mmHg) or less.

In the organic chemistry laboratory, there are two kinds of vacuum pumps: a water pump and a vacuum pump. If a low pressure is not required, a water pump is available. If the water pump has a good structure and a high water pressure, the pumping efficiency can reach 1067 to 3333 Pa (8 ~25mmHg) . The minimum pressure that a pump can draw is theoretically equivalent to the water vapor pressure at that time. For example, when the water temperature is 25 °C, 20 °C, and 10 °C, the pressure of water vapor is 3192 , 2394 , and 1197Pa (8-25mmHg), respectively . When using a water pump to pump air, install a safety bottle in front of the pump to reduce the water pressure and draw back the water. Before stopping the pumping, you should vent the air and then turn off the water pump.

Structural features

(1) Larger pumping speeds over a wider pressure range;

(2) The rotor has a good geometrical symmetry, so the vibration is small and the operation is smooth. There is a gap between the rotor and between the rotor and the housing, no lubrication, small friction loss, can greatly reduce the driving power, which can achieve higher speed;

(3) No oil sealing and lubrication inside the pump chamber can reduce the pollution of the vacuum system by oil vapor;

(4) There is no compression in the pump chamber and no exhaust valve. Simple and compact structure, insensitive to dust and water vapor in the exhausted gas;

(5) The compression is relatively low and the effect of hydrogen pumping is poor;

(6) The surface of the rotor is a curved cylindrical surface with complex shapes, making machining and inspection more difficult.

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