9
The use of a cold trap when pumping heavy vapor loads will eliminate the need for a liquid
trap attached to the exhaust port. The cold trap is installed between the pump and the vacuum
chamber. The water or organic vapors evolved from the vacuum process will upon entering
the cold trap will come in contact with the surfaces of the trap and condense. Commonly used
refrigerants are liquid nitrogen or dry ice with alcohol slurry. Dry ice provides suffi cient cooling
to freeze out most heavy water vapor loads. A variety of cold traps are available from Welch.
Please call our customer service department. For additional information at (847) 676-8800.
2.19 The Care of a Liquid Trap
A liquid trap needs no refrigerant. The key maintenance issue when pumping high vapor loads
is to regularly drain the trap of liquid ejected from the dry vacuum pump.
2.20 The Care of a Cold Trap
When using a cold trap the refrigerant should be maintained at a high level in the fl ask to keep
the trap at a uniformly low temperature. If the trap is rewarmed it may allow re-evaporation of
the condensate. The refrigerant add tube on the liquid nitrogen trap should not be obstructed
as the refrigerant boil-off can produce dangerously high pressures. If the trap becomes
saturated it should be disconnected from the system, drained and cleaned. An increase in
pressure in the vacuum system will normally indicate that the trap has become saturated.
To clean the trap, remove the trap from the system and allow the trap to warm up and rinse
off the condensate with a suitable solvent in a fume hood. Thoroughly clean and dry the trap
before reinstalling into the system. If a liquid nitrogen trap is used, the refrigerant add tube
on the liquid nitrogen trap should not be obstructed as the refrigerant boil-off can produce
dangerously high pressures.
Dry Vacuum Pump
Dry Vacuum Pump
Liquid
Trap
Cold Trap
Rotary Evaporator
Rotary Evaporator
To Fume
Hood
