Welch Vacuum 2028 Self-Cleaning Dry Vacuum System - Manual (Page 7)

The temporary adapter should be used only until a properly grounded outlet (Sketch A) can be installed
by a qualifi ed electrician. When using the temporary adapter, the green colored rigid ear, lug, etc.
extending from the adapter must be connected to a permanent ground such as a properly grounded
outlet box cover. Whenever the adapter is used, it must be held in place by a metal screw.
2.24 Extension Cords
If necessary to use an extension cord, use a 3-wire extension cord that has a 3-blade grounding plug,
and a 3-slot receptacle that will accept the plug on the product. Make certain your extension cord is
in good condition. Make certain your extension cord wire size is not less than 18 gauge for 25 feet,
16 gauge for 50 feet, and 14 gauge for 100 feet. An undersized cord will cause a drop in line voltage
resulting in loss of power and overheating. If in doubt, use the next heavier cord. The smaller the gauge
number, the heavier the cord. Avoid routing the extension cord through areas that could result in damage
to the cord.
2.30 Traps
2.31 When To Use A Trap
The Self-Cleaning Dry Vacuum System is constructed of PTFE or fl uorinated plastics on all wetted
surfaces to resists chemical attack from aggressive solvent, base and acid vapors. A totally oil free
diaphragm mechanism removes the need for lubricating and sealing fl uids for pulling a vacuum. When
pumping gases or low vapor loads, a trap is not necessary unless you want to capture vapors evolved
from the process. When a heavy load of water or organic vapor is evolved from the vacuum process,
condensation of vapor in the pump mechanism may occur. The reason is the pump is compressing
the vapor as it passes through the pump. If the vapor is dense enough, the compression will cause
condensation of the vapor in the pump mechanism. The valve system in the pump mechanism is
designed to pass the small quantity of liquefi ed vapor formed when pumping heavy vapor loads. The
liquid formed will be ejected from the outlet port. The self-cleaning purge feature of the Self-Cleaning Dry
Vacuum System is designed to eject condensed vapors left in the pump up on shut-done.
The advantage of a cold trap when pumping heavy vapor loads is that it will increase the effective
pumping speed of the Self-Cleaning Dry Vacuum System. 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 time savings will depend on such factors as the solvent stripped,
solvent temperature and operating temperature of the cold trap.
The cold trap is installed between the pump and the vacuum chamber. The water or organic vapors
evolved from the vacuum process entering the cold trap will come in contact with the cold 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. Visit the Welch Web-Site at www.welchvacuum.com.
2.32 Solvent Traps
Your Self-Cleaning Dry Vacuum System comes with a basic solvent removal capability to remove
readily condensable solvents prior to pump ingestion and to collect solvent accumulated during pump
condensation and the Self-Cleaning cycle. Solvent removal can be further enhanced to provide additional
pumping effi cacy, safety, solvent fate control, and pump life. Depending upon your application, additional
solvent trapping may be desirable. Solvent trapping confi gurations are discussed below; consult your
Welch representative for application specifi c trapping recommendations.
2.33 Self-Cleaning Dry Vacuum System Solvent Removal
When pumping gases or low vapor loads, a trap is not necessary unless you want to capture vapors
evolved from the process. When a heavy load of water or organic vapor is evolved from the vacuum
process, condensation of vapor in the pump mechanism may occur due to compression. The valve
system in the pump mechanism is designed to pass a small quantity of liquefi ed vapor formed when
pumping heavy vapor loads. The liquid formed will be ejected from the outlet port. The self-cleaning
purge feature of the Self-Cleaning Dry Vacuum System is designed to eject condensed vapors left in the
pump upon shut-down and collect condensate in the side-mounted jar.
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