How is the vacuum furnace can not pumping out the air

If there is liquid in the usual test, a liquid evaporation process (gasification can happen without heating under high vacuum) is required. It is possible to vaporize this part of the liquid by pulling the vacuum for a long time to achieve high vacuum (waiting for the vacuum stable ).

If the target air pressure is not reached for a long time, it is necessary to consider the system and the Roots pump. You can directly measure the ultimate vacuum of the Roots pump (not connect into other systems). If the roots pump is fine, then the sealing performance of the system need to be considered.