Welch Vacuum 2585B-50 WOB-L Pinston Pump - Manual (Page 7)

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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 adapt
er is used, it must be held in place by a metal screw.
2.25 Extension Cords
I f 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”Hg) 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 different 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 in Hg).
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 different maximum vacuum readings from day to day.