8
The symptom of a high water vapor load is if you have droplets coming out of the exhaust
port. If you see droplets of water, Welch recommends you use a cold trap to capture the water
before entering the pump or dilute the water vapor stream by adding dry nitrogen to the gas
fl ow. Please call our customer service department for additional information at (847) 676-8800.
2.92 The Care of a 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.
