Vacuum Leak Detection Technology

1. What is air leakage and ventilation?

Vacuum equipment is required to achieve and maintain a vacuum state. If there is a leakage problem, it will become a major defect. At the same time, no vacuum equipment has absolute tightness, there is a certain degree of leakage problems.

The phenomenon of gas passing through solid is called gas permeability, especially the hydrogen and helium gas passing through the sealing with rubber material can not be ignored. But the nature of air permeability is different from that of air leakage. Leakage is defined as the phenomenon of mechanical intrusion from the high-pressure side to the low-pressure side of a gap or hole.

2. Reasons for Leakage

The main cause of air leakage is the defect of the material itself, and the other is the bad sealing part. Another situation is that there is no leakage at room temperature, but when the temperature changes, there will be leakage. The main reason for this is the difference of thermal expansion coefficient.

3. Admissible range of air leakage

Strictly speaking, air leakage exists in any equipment. The problem is whether the air leakage has an effect on the vacuum equipment and the purpose of use. The effect of air leakage is that it may affect the pressure reached or the purity of the experimental production. If such adverse effects can not be caused, a certain amount of leakage can be allowed in a certain range. Generally speaking, the air leakage shown in the table below is acceptable.


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Helium mass spectrometer leak detector principle

1. Structure of helium mass spectrometer leak detector (30D, 542, etc.)

2. mass spectrometry room

3. Vacuum system

4. Electrical System

5. How to select helium mass spectrometer leak detector

6. The content of air is very little.

7. Helium molecule is small, light and easy to pass through the leak. After entering the system, the flow and diffusion are also fast.

8. The helium ion mass-charge ratio is small, so the deflection radius is small, the size of the analyzer can be smaller, or the weak magnetic field can be used.

Helium mass spectrometer leak detector principle

1. The helium mass spectrometer leak detector is a kind of gas tightness detection instrument based on the principle of mass spectrometry, which uses helium as exploratory gas. The principle of mass spectrometry is as follows:

2. Electrons emitted by filament heat are accelerated into the ionization chamber, and collide with residual gas molecules and helium gas leaked into the ionization chamber to ionize them into positive ions. These ions enter the magnetic field under the accelerated electric field and deflect due to the action of magnetic field force (Lorentz force), forming a circular arc orbit.

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Helium mass spectrometer leak detector

Helium mass spectrometer is a term used in gas industry. It uses helium or hydrogen as leak gas and uses gas analyzer to detect helium. The background noise of helium is low, its molecular weight and viscosity coefficient are small, so it is easy to pass through the leak hole and diffuse easily. In addition, helium inert gas does not corrode the equipment, so helium is often used as the leak indicator gas. The gas is sprayed onto the tested vessel with a gas analyzer (adjusted to the working state of helium reaction only). If there is a leak in the vessel, the analyzer will react, so as to know the location of the leak and the size of the leak.

Helium mass spectrometer for leak detection in power plants. The key components are imported, and the performance is stable and reliable. It not only has high sensitivity, but also is easy to operate. It can automatically switch between two filaments, adjust zero automatically, calibrate automatically and switch between automatic ranges.

Helium mass spectrometer leak detector advantages:

1. Portable design

2. The appearance of the equipment is beautiful and compact.

3. Design of LCD Touch Screen

4. Communication interface

5. Leak detection data can be easily output


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How to Install Rotary Vacuum Pump

Reasonable installation of rotary vane vacuum pump can not only ensure the normal operation of the pump, but also prolong the service life of the pump. Then how to install rotary vane vacuum pump correctly? Next, vacuum pump experts will introduce the installation method of rotary vane vacuum pump for you.

First, after opening the box, carefully remove the rotary vane vacuum pump body, spare accessories and instructions and keep them for future reserve. Remove the filler and wipe off the dust and dirt on the surface of the pump. Count the number by packing list.

Secondly, the rotary vane vacuum pump is installed in the room with clean environment, good ventilation and sufficient light to meet the requirements of Article 4. Pumps should be installed in a certain ample site according to the use, so as to facilitate operation and maintenance. See the shape and size of the pump. Rotary vane vacuum pump can be placed on a solid flat ground, without special foundation. If it needs to be fixed, additional screw and foundation can be firmly fixed. See the size of foot screw. If the rotary vane vacuum pump is close to the precision instrument, it should be considered to add shock-proof device.

Connect the vacuum hose or flange to the rotary vane vacuum pump. If the flange is connected, there should be rubber groove on the flange. See figure 50 for the form and size of the flange. The diameter of the pipe connecting the pumped container should not be less than the diameter of the pump intake, the pipe should be short, and the joint should be less. Otherwise, the pumping speed should be affected, and the leakage of the pipe and joint should be small. The gas volume of the pumped container should be in accordance with the pumping speed of the pump. The relationship between the pumping speed of the rotary vane vacuum pump is shown in Fig. 4. It is suggested that a vacuum valve be installed between the pump and the pumped container to control the gas flow. For pumps, it is recommended to install a vent valve (or solenoid valve) to vent the pump when it stops, which can prevent oil return and start easily.

Then, the power supply is connected according to the voltage and wiring mode indicated by the motor sign, and it is suggested that the safety device be used to avoid overload, and the direction of motor rotation should be determined in accordance with the direction of arrow on the pump. Remove the exhaust plug and install the exhaust hood, or remove the sleeve on the exhaust nozzle. The rotary vane vacuum pump needs the cooler to connect to the water source.

Finally, if it is necessary to remove toxic and corrosive ferrous metal gases, gases with chemical changes to vacuum oil, and gases with dust and atmospheric temperature, relevant devices such as neutralization, cooling and filtering should be installed in the intake pipeline to cooperate with the use, otherwise the performance and service life of rotary vane vacuum pump will be affected. When extracting harmful gases to human body, corresponding pipes should be installed to lead the exhausted gases outdoors away from the work area for treatment.

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Water Ring Vacuum Pump Characteristics

Water ring vacuum pump can transport both gas and liquid. Only in pumping liquid time efficiency is low. When conveying gas, it can also be used as a low-pressure compressor. Its discharge pressure is about 0.1-0.2 MPa. Its exhaust volume ranges from 0.25 to 30 m_per minute. The vacuum degree can reach 70-80%, and 99.5% when it is manufactured well.

When the pumped gas is not suitable for contact with water, the pump can be filled with oil or other liquid medium (often referred to as liquid ring pump). If oil is used as working medium, the first vacuum degree can reach 99.98%, and the second vacuum degree can reach 99.999%.

The greatest advantage of water ring vacuum pump is that it can suck gas containing liquid. In the use of vacuum system, there are a lot of quiet conditions in the inhalation containing cloudy liquid. Even if it contains swallow vapor, it must be liquefied in the compression process, and the general reciprocating pump is not suitable for such suction. Because the liquid is enclosed between the piston and the cylinder head, the existence of the liquid makes the valve and other channels too narrow. The greater the gas resistance, that is, the loss of power. The water ring vacuum pump is originally based on the liquid as the piston, so it is completely harmless to contain liquid in the suction.

This type of pump is in addition to the above. There are also the following advantages

(1) Except for bearings and sealing caps. There are no other mechanical contact parts such as valves and pistons in its air system, so no internal lubrication is required. The utility model has the advantages of simple structure, easy manufacture and maintenance, reliable operation and long service life of the machine.

(2) Because of the high speed, the pump can be directly connected with the motor, so the exhaust is continuous and uniform. · For a certain displacement, it is small, compact and occupies less space.

(3) Because the liquid in operation is circulated internally, it can avoid the heat caused by the discharging of soup and compression of gas, so it is also suitable for the extraction of toxic or explosive gases. Not only can pressure group, acetylene and biogas be used, but also there is no problem if concentrated sulfuric acid is used instead of water for the very difficult gas capture by reciprocating pump.

Water ring vacuum pump has many advantages, so it has been widely used in petroleum and chemical production. The disadvantage is that the efficiency of this kind of pump is very low. It is about 0.3-0.5.

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Vacuum Pump in Chemical Plant

Any pressure below atmospheric pressure is called vacuum. Vacuum is the degree below atmospheric pressure, usually expressed in percentage or millimeter water column (or mercury column). If the vacuum degree of a certain equipment is 80%, it means that the pressure in the equipment is 20% of the atmospheric pressure, that is, when the atmospheric pressure is 1 kg/cm, the pressure in the equipment is 0.2 kg/cm. Therefore, when the percentage is used to indicate the degree of vacuum, it is to indicate the degree of gas extraction. When expressed by a millimeter water column, the residual pressure is expressed. If the vacuum in the spare water column is 3x10-2mm, the pressure in the equipment (i.e. residual pressure) is 3x10-2mm water column.

In chemical plants, some production processes are often carried out under atmospheric pressure, such as vacuum evaporation, vacuum distillation and vacuum suction and filtration.

In order to achieve vacuum, it is necessary to have a vacuum pump, which is the equipment to extract gas. Vacuum pumps can be roughly divided into reciprocating, rotary and jet pumps.

1. Reciprocating vacuum pump

The principle of reciprocating vacuum pump and reciprocating compressor is exactly the same, but the valve distribution mechanism is different from the intake and exhaust valves. Spring valves are generally used in reciprocating compressors, while the so-called sliding valve valve valve distribution mechanism is mostly used in reciprocating vacuum pumps.

2. Water ring vacuum pump

Water ring vacuum pump is a kind of rotary vacuum pump. It can be used for compressed gas besides suction gas. for example

The maximum pressure of gas discharged by water ring vacuum pump can reach 1.5 kg/cm, so it is also called water ring compressor. This kind of pump should avoid solid particles entering the pump body when working.

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Low vacuum pumping unit

The main features of the low vacuum unit are high working pressure and large displacement, but the pumping speed is lower than that of the high vacuum unit. It is widely used in vacuum pumping and vacuum pumping, vacuum impregnation, vacuum filtration, vacuum drying, vacuum degassing (steel water treatment) and other devices.

The main pumps of low-vacuum pumping units are commonly used reciprocating vacuum pumps, oil-sealed mechanical pumps, dry mechanical pumps, water jet pumps, water jet pumps, water ring pumps, molecular sieve adsorption pumps, wet Roots pumps and other straight-through atmospheric vacuum pumps. The use of low-vacuum pumping units also requires the necessary dust collectors, water-gas separators, oil-water separators, dry bath traps, etc., depending on the degree of gas cleaning, humidity or other special requirements.

(1) Measures for oil seal mechanical pump unit to remove condensable gas.

The oil seal mechanical pump is not suitable for pumping out gas containing a large amount of water vapor. The water vapor will condense into water droplets during the compression process, and mix with the pump oil to form a suspension, which will destroy the pumping performance of the pump and reduce the vacuum degree of the pump. The general measures are: using an oil-sealed mechanical pump with gas ballast and controlling the working temperature of the pump between 75-90 °C to reduce the burden of the gas ballast; installing a water vapor separator or oil-water separation in the unit The catching machine processes the mechanical pump oil mixed with water, and the treated oil is used in a human pump; the various adsorbents are used to make the trap absorb water vapor. The use of various condensers or cold traps not only effectively adsorbs water vapor, but also blocks the return flow of the mechanical pump to the vacuum chamber.

(2) Commonly used unit forms.

Oil seal mechanical pump low vacuum unit. Suitable for chemical vapor deposition equipment, vacuum packaging, pharmaceutical industry and other fields.

Low vacuum unit with oil trap. The ultimate pressure of the unit consisting of a two-stage water ring pump and an atmospheric jet pump is 1300Pa. When working, first start the water ring pump to obtain the pre-pressure required for the atmospheric jet pump, so that there is a pressure difference between the air inlet and the air outlet of the atmospheric jet pump, and the atmosphere is injected into the pump to form a high-speed moving airflow. The gas will be sucked and discharged by the water ring pump through the diffuser.

The unit is suitable for vacuum evaporation, vacuum concentration, vacuum immersion, vacuum dry coal, vacuum freezing and other processes.

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