7
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 Band 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 Dial Vacuum Gauge
A dial vacuum gauge is incorporated in the vacuum system. The dial gauge is located in the
top front section of the system. The dial vacuum gauge is commonly used to indicate vacuum
level when operating in the rough vacuum range (0 to 29.9 InHg) Dial vacuum gauges give
negative pressure - that is pressure below atmospheric. The reference point for the gauges
is atmospheric pressure. Please keep in mind that atmospheric pressure tends to vary from
day to day
. As a result of this variability, a dial vacuum gauge will indicate slightly diff erent
maximum vacuum readings from day to day.
2.27 Vacuum Level Regulation
Vacuum level regulation is accomplished with an adjustable bleed valve. The adjustable bleed
valve allows close control of pressure in your apparatus. Pressure may be set between roughly
atmospheric pressure and the maximum vacuum obtainable (9 torr, 29.6 InHg).
2.28 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.
2.29 Vacuum Gauges
Typical in the rough vacuum range, a dial vacuum gauge is used to measure pressure in mm,
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 diff erent maximum vacuum readings from day to day.
Summary of Contents for WELCH 2567B-01
Page 12: ...12 6 11 Pumping Speed Curves...
