Welch Vacuum 2561B-50 WOB-L Pinston Pump - Manual (Page 7)

The adapter shown in Figure #1 B and C is not acceptable in Canada.
2.65 Extension Cords
Motor thermal overload protection is made available by the motor manufacturer as an aid to
minimize motor failure. Overload protection is a standard feature on both 50 and 60 Hz single
phase-motors. The motors have automatic overload protection. Automatic reset protection is
designed to reset itself after a predetermined cooling period. If the fault to the drive remains
unaltered, the motor will cycle on and off until the fault is corrected.
2.70 VACUUM CONNECTIONS
2.71 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 four models operate in the viscous fl ow regime, 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.
2.80 VACUUM GAUGES
2.81 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.
2.90 TRAPS
2.91 The need of 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.
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