The foreline pump is a vacuum pump used to maintain the pressure at the anterior stage of a vacuum pump below its pre-critical pressure level. Such as Roots pump configuration before the rotary vane pump or pump is the forefront pump. Use of the foreline pump: The term forepump in the vacuum unit to see more of this term, mainly to help the main pump Roots vacuum pump start. Roots vacuum pump under normal circumstances can not be started under atmospheric pressure, if you want to start the motor power is quite large, and the pump operation is hurt. By using a different fore pump can be applied to different environments. If equipped with a water ring vacuum pump, you can pump out a large amount of condensable vapor and corrosive gases (dilution of corrosive gas by water concentration). At present, the common forecourt pumps are: water ring vacuum pump, rotary vane vacuum pump, vertical oil-free vacuum pump, reciprocating vacuum pump, H, 2H slide valve vacuum pump and so on. Through the choice of different fore pump can get a different degree of vacuum and pumping rate.
Wood is divided into two distinct kinds called hardwood and softwood, though confusingly the names don't always refer to its actual hardness or softness:
Hardwoods typically come from broad-leaved (deciduous) trees (those that drop their leaves each fall, also known as angiosperms because their seeds are encased in fruits or pods). Examples include ash, beech, birch, mahogany, maple, oak, teak, and walnut.
Softwoods typically come from evergreen (coniferous) trees (those that have needles and cones and retain them year-round, also called gymnosperms. Examples include cedar, cypress, fir, pine, spruce, and redwood.
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