The main characteristics of low vacuum unit are high working pressure and large exhaust volume, but the pumping speed is lower than that of high vacuum unit. It is mainly used in the crude pumping of vacuum chamber, vacuum conveying, vacuum impregnation, vacuum filtration, vacuum drying, vacuum degassing (steel treatment) and other devices with large outgassing volume and high working pressure.
The main pumps of the low vacuum pumping unit are usually reciprocating vacuum pumps, oil sealed mechanical pumps, dry mechanical pumps, water jet pumps, steam jet pumps, water ring pumps, molecular sieve adsorption pumps, wet Roots pumps and other direct discharge atmospheric vacuum pumps. When the low vacuum pumping unit is used, necessary dust collectors and water gas separators shall be equipped according to the degree of purge, humidity or other special requirements of the extracted gas , oil water separator, dry bath well and other components.
(1) measures for oil seal mechanical pump unit to pump out condensable gas.
Oil sealed mechanical pump is not suitable for pumping gas containing a large amount of water vapor. Water vapor will condense into water droplets in the process of compression, and mix with pump oil to form suspension, which will damage the pumping performance of the pump and reduce the vacuum degree of the pump. The general measures to be taken are: use the oil seal mechanical pump with gas ballast dish, and control the working temperature of the pump between 75-90 ℃, so as to reduce the burden of gas ballast valve; install the water vapor separator or oil-water separation device in the unit, treat the mechanical pump oil mixed with water, and then use the treated oil in the pump; use various dry adsorbents to make a trap to absorb water vapor. The use of various condensers or cold traps can not only effectively absorb water vapor, but also prevent the mechanical pump from flowing back to the vacuum chamber.
(2) common unit forms.
Oil sealed mechanical pump low vacuum unit is suitable for chemical vapor deposition device, vacuum packaging, pharmaceutical industry and other fields.
Low vacuum unit with oil trap. The ultimate pressure of the unit composed of two-stage water ring pump and air jet pump is 1300pa. When working, first start the water ring pump to obtain the pre pressure required by the air jet pump, so that there is a pressure difference between the air inlet and the air outlet of the air jet pump, and the air will form a high-speed moving air flow through the injection into the pump. The pumped gas will be drawn into the pump and discharged by the water ring pump through the diffuser.
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