Ultra-high vacuum extraction unit

Ultra-high vacuum extraction unit


The ultra-high vacuum unit works in the ultra-high vacuum pressure range of 10-6-10-10Pa.

Low, low leakage rate, can withstand high temperature baking at 200 ~ 450 ℃, the requirements for the unit are:

(1) The ultimate vacuum of the main pump should be high, at least above 10-7 ~ 10-8Pa;

(2) The main pump has a certain pumping speed within the working pressure range of the ultra-high vacuum;

(3) The main pump of the unit or above the air inlet of the main pump can withstand high temperature baking at 200-450 ℃;

(4) The partial pressure of the return gas from the main pump (including the working fluid vapor and the analytical gas) must be sufficiently low.

(5) The main pump with strong selectivity of the pumped gas should be equipped with a sufficiently large auxiliary pump;

(6) For the pipes, valves and other components above the air intake of the main pump of the unit, the selection and sealing of materials must be especially careful. Generally, stainless steel with low outgassing rate and metal sealing material are used to resist high temperature baking.

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Determination of vacuum exhaust volume of vacuum pump

Determination of vacuum exhaust volume of vacuum pump


(I) Performance index of vacuum pumping speed

The time for the vacuum system of the lyophilizer to pump from atmospheric pressure to 10Pa should not exceed 30min.

(B) the selection principle of vacuum pump

① The ultimate vacuum of the selected main vacuum pump should be 1 to 2 orders of magnitude higher than the ultimate vacuum required by the lyophilizer. Pharmaceutical freeze-drying generally requires a limit vacuum of 1 ~ 5Pa, and the limit vacuum of the main vacuum pump selected should be higher than 1X10-1 ~ 1X10-2Pa. Rotary vane pump, slide valve pump, roots pump, oil booster pump are all available.

② The working vacuum degree of the freeze-drying box is 4 ~ 4OPa, which should be within the optimal pumping pressure range of the main vacuum pump.

③ The vacuum pump used by the lyophilizer should also be able to remove some water vapor, or it can be adapted to be mixed with water vapor by the pumped gas.

(III) Calculation of pumping rate

The freeze-drying machine has a pre-pumping time requirement. This time requirement is very important when the cold trap and the freeze-drying box share a refrigerator. Failure to meet the requirements may cause the pre-frozen product to melt. If the vacuum condenser (cold trap) is used for cooling while the lyophilizer can still be kept cold at low temperature, this time requirement is not so important. In other words, the required time can be appropriately extended, but this has a slight impact on the performance of the freeze dryer.

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Vacuum pumps in refrigeration equipment

Vacuum pumps in refrigeration equipment

When repairing air-conditioning and refrigeration equipment, the repairman often uses a vacuum pump to evacuate the system. The vacuum should be -0.1MPa for 24 hours, and the vacuum can be increased without significant increase.

1. Structure and working principle of vacuum pump

A commonly used vacuum pump is a rotary vane vacuum pump, which is a mechanical pump sealed with a pump oil and has a structure.

It can be seen that the outer circle of the rotor is tangent to the inner surface of the pump cavity, and the rotary blade is installed in the rotor pick, and is always in close contact with the wall of the stator cavity under the action of the spring. When the eccentric rotor rotates under the drag of the motor, the rotor also rotates. When rotating clockwise, the suction port keeps inhaling gas. The intake cavity keeps expanding. At the same time, the exhaust cavity is getting smaller and smaller, and the gas that has been inhaled is completely compressed. The air pressure rises, and after reaching a certain pressure, the exhaust valve can be opened through the pump oil and discharged through the exhaust pipe. This continuous circulation can play the role of vacuum extraction.

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Precautions to prevent damage to the vacuum pump

Precautions to prevent damage to the vacuum pump

In the case of a small gap, when the temperature rises, the vacuum pump cover will expand, but the pump casing will prevent the cover from expanding. Because of this, a lot of stress is generated in the pump casing, and it even bursts.

In order to prevent the vacuum pump from being damaged due to temperature stress, the following points should be noted:

(1) Insulate the housing of the vacuum pump well;

(2) Heat the vacuum pump slowly and evenly before starting:

(3) Avoid cooling the fog parts containing high temperature parts;

(4) All fittings on the pump casing should be carefully checked based on temperature stress;

(5) The alignment of the shaft and bearing should be checked in a cold state, in a warm-up period, and in a hot state to prevent the shaft from deforming at any temperature.

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Application and main classification of vacuum pump in chemical plant

Application and main classification of vacuum pump in chemical plant

Any pressure below atmospheric pressure is called vacuum. The degree of vacuum is the degree below atmospheric pressure, which is usually expressed as a percentage or millimeter of water (or mercury). If the vacuum degree of a certain equipment is 80%, it means that the pressure in the equipment is changed to 20% of the atmospheric pressure, that is, when the atmospheric pressure is 1 kg / cm², the pressure in the equipment is 0.2 kg / cm². Therefore, when the degree of vacuum is expressed as a percentage, it indicates the degree to which the gas is extracted. When expressed in millimeters of water column, it indicates its residual pressure. If the vacuum in the device is 3x10-2 millimeters of water column, it means that the pressure in the device (that is, the residual pressure) is 3x10-2 millimeters of water column.

In chemical plants, certain production processes are often performed under atmospheric pressure, such as vacuum evaporation, vacuum distillation, and vacuum filtration.

In order to reach the vacuum, it is necessary to have a device that extracts the gas-a vacuum pump. Vacuum pumps can be roughly divided into reciprocating, rotary and jet pumps.

Reciprocating vacuum pump

The principle of the reciprocating vacuum pump and the reciprocating compressor are exactly the same, except that the air distribution mechanism, that is, the intake and exhaust valves are different. Spring valves are generally used in reciprocating compressors, and so-called slide valve air distribution mechanisms are mostly used in reciprocating vacuum pumps.

2.Water ring vacuum pump

Water ring vacuum pump is a kind of rotary vacuum pump. In addition to pumping gas, it can also be used for compressed gas. E.g

The maximum pressure of PMK-2 water ring vacuum pump exhaust gas can reach 1.5 kg / cm², so it is also called water ring compressor. This type of pump should avoid solid particles entering the pump body during operation.

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Method for obtaining vacuum of vacuum pump

The obtaining of vacuum is the main component of vacuum technology. With a variety of methods, a certain degree of vacuum can be obtained in the pumped container. The range of currently available vacuum is quite wide, from 100kPa to 10-11Pa. In other words, it should be from 100kPa to 10-4Pa.

Therefore, different methods should be used to obtain vacuum according to different vacuum requirements and use conditions. The existing methods to obtain vacuum can be roughly divided into the following three categories: vacuum pumps (such as mechanical pumps, diffusion pumps, etc.), getters (red Phosphorus, barium aluminum, titanium, ZrAl16, etc.) and vapor traps (cold traps, dryers, etc.). In the electric light source industry, the main means to obtain a vacuum is to rely on a mechanical vacuum pump and a vapor flow diffusion vacuum pump.

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Component structure of oil-free vacuum system

In recent years, it has been found that vacuum systems that use mechanical vacuum pumps and diffusion pumps to evacuate, because it has enough oil vapor to flow back into the pumped container or device, the performance and technical indicators of many electronic devices are seriously affected. For example, the oxide cathode of an electronic tube reduces its emission performance and life due to oil vapor. Various high-power high-voltage electronic tubes are prone to electrical breakdown due to the presence of oil vapor. The presence of the oil significantly reduces its pressure resistance index, and oil vapor has a significant adverse effect in many places.

Therefore, the vacuum systems used in these areas are required to be replaced by oil-free vacuum systems, that is, instead of using vacuum oil sealing tools (such as mechanical pumps, diffusion pumps) that use vacuum oil seals and vacuum oil as the working fluid, Adsorption of gas molecules, adsorption pumps and pumps that reduce the pressure in the container to obtain the required vacuum.

The adsorption pump uses the porous surface of certain solid materials to strongly adsorb gas in a cold state, so that the closed system obtains a low vacuum of 10-2 mm mercury column. It is used as the front stage of an oil-free system .

Generally, in addition to activated carbon, the adsorbent used by the adsorption pump uses a molecular sieve (artificial zeolite) to adsorb the gas and obtain a vacuum. Because, after cooling with liquid nitrogen, each kilogram of molecular sieve can draw a 50-100 liter container from the atmosphere into a vacuum of 10-2 mm mercury column, so it is a kind of pump with a large air intake. After it is baked at about 400 ° C, the gas it absorbs is released again (called activation or regeneration), and the ability to re-inhale is restored. 5A molecular sieves currently used (large absorption capacity, suitable for exhausting air, but need to be "activated, with an average pore size of about 5 Angstroms) and 13X molecular sieve (its adsorption capacity is smaller than 5A molecular sieve, but it can absorb oil vapor molecules) .

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