This product is for use on a nominal 120V circuit, and has a grounding plug that looks like the plug illustrated
in Sketch A in Figure #1. A temporary adapter, which looks like the adapter illustrated in sketches B and C,
may be used to connect this plug to a 2-pole receptacle as shown in sketch B if a properly grounded outlet
is not available. The temporary adapter should be used only until a properly grounded outlet (Sketch A) can
be installed by a qualifi ed electrician. 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.
2.25 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.
2.26 Vacuum
Connections
All Dry Vacuum Pumps come with intake and discharge hose barbs which accept 3/8” ID rubber
pressure/vacuum hose. Hose clamps should be used to hold the hose in place. Since all six models
operate in the viscous fl ow range, the small diameter of the hose will generate minimal conductance
loss. For best results, Welch recommends the length of the tubing between the pump and the chamber
be kept as small as possible.
2.27 Vacuum
Gauges
Typically in the rough vacuum range, a dial vacuum gauge is used to measure pressure in mm of Hg
or inches of Hg. The dial vacuum gauge gives negative pressure – that is pressure below atmospheric.
The reference point for the vacuum gauge is atmospheric pressure. Please keep in mind that
atmospheric pressure tends to vary from day to day. As a result of variability, the dial vacuum gauge will
indicate slightly different maximum vacuum readings from day to day.
2.30 Traps
2.30a
The need for a Trap
The pumps will handle humid air. All wetted aluminum parts are treated for corrosion protection from
moisture. All other wetted parts are stainless steel. If there is a chance liquid may be drawn from the
process under evacuation, Welch recommends a liquid trap be placed between the process and the
pump. A simple liquid trap is a fi ltering fl ask.
When a heavy load of water vapor is evolved from the vacuum process, a cold trap is recommended
to help prevent damage to the pump mechanism. The cold trap, immersed in a suitable Dewar fl ask,
is installed so that the water vapor may come in contact with the surfaces of the trap and condense.
Commonly used refrigerants are liquid nitrogen or dry ice and acetone or alcohol. Dry ice provides
suffi cient cooling to freeze out most heavy water vapor loads. A variety of cold traps are available from
Welch.
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.
2.30b 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 re-warmed 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.
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