Welch Vacuum 2028 Self-Cleaning Dry Vacuum System - Manual (Page 8)

2.34 Cold Trap Solvent Removal
Condensation of organic solvent fumes is typically accomplished by suspending a trap in a Dewar fl ask
containing dry ice / isopropanol slurry or liquid nitrogen. Alternatively low maintenance cooling to -100
o C
can be achieved using a refrigerated cold trap. The cold trap is connected between the application and
the pump unit to prevent solvent ingestion. Installation of a cold trap when pumping heavy vapor loads
offers several advantages:
• The Self-Cleaning Dry Vacuum System will operate more effi ciently. The trap acts as an additional
pumping mechanism, increasing the effective pumping speed. This higher effective pumping speed will
shorten the time needed to strip solvent.
• The absence of a high solvent load in the pump diaphragm mechanism promotes pumping effi ciency
and extends diaphragm life.
• Vacuum pump pass-through of solvents is reduced, preventing possible discharge into the laboratory
atmosphere and enabling responsible control of chemical usage and potential solvent recycling. A variety
of cold traps are available from Welch. Contact your closest Gardner Denver Welch Vacuum Technology
sales offi ce or visit the Welch Web-Site at www.welchvacuum.com.
2.35 CAPTURE TM Cold trap
Your Welch Self-Cleaning Dry Vacuum System can be extended to include a CAPTURE TM cold trap.
This trap is a pump-mounted condenser utilizing recirculating chilled water can be confi gured to remove
solvent fumes from the vacuum stream either prior to the pump inlet to lessen solvent ingestion or on
the pump outlet to reduce emissions. The CAPTURE
trap provides continuous solvent condensation
without the need to recharge a cold trap with dry ice / isopropanol or liquid nitrogen. Contact your Welch
representative for more CAPTURE information or see www.welchvacuum.com
2.36 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.
2.37 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. 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 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.
2.38 Application Note for Cold Trap
Cold traps employing a dry ice slurry or liquid nitrogen are effective as long as the refrigerant level
is maintained. If the trap warms up while the pump is running, all of the trapped condensable will be
ingested by the vacuum pump. Cold traps must be cleaned out at the end of each day. If the pump is
run overnight, the trapped condensable will ultimately be ingested by the pump as the trap warms up.
Cleaning a Dry Ice Slurry/Liquid Nitrogen trap is easy. The steps are:
1. Turn off the pump.
2. Leak air into the trap.
3. Remove the center well and Plexiglas ring to a hood. The center well can be washed off into a
beaker or the condensable can be allowed to evaporate in the hood.
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