Chemglass AF-0350 Welch Vacuum Pump - Manual (Page 4)

1.6 Electrical Power
1.6a Power source Review
Review the power source and the motor rating to be sure they agree in voltage, phase and frequency. On three-phase
applications the direction of rotation of the motor must be considered. Make a momentary check rotation at the time of
power installation and wiring. Momentary backward rotation of the pump is not harmful. Check the layout drawings for
proper direction of rotation.
CAUTION
Make certain the power settings on the pump match your power
source before attempting to operate the pump
1.6b Overload Protection
Motor thermal overload protection is made available by the motor manufacturer as an aid to minimizing motor failure.
Overload protection is a standard feature on all single-phase 60Hz motors. Single-phase motors will normally have
automatic overload protection. Motors of 1-1/2 horsepower or larger supplied with DUOSEAL pumps contain no
overload protection. Installations of such equipment must comply with local electrical codes which dictate appropriate
starter and protection devices. It is strongly suggested that you familiarize yourself with the protection supplied with
your motor so that you may react accordingly in the event of an emergency. 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. The motor data plate will indicate the presence of thermal protection.
1.7 Vacuum Connections (See Accessory Section in back of this manual.)
1.7a Choice of Connections
The choice of connections and fitting can have a very marked effect on the pumping speed at the vacuum chamber. Any
connection placed between the pump and the chamber creates an impedance to the flow of gas. This is particularly true at
low pressures in the millitorr range where the gas flow is substantially molecular in character. The gas flow is then
dependent upon the kinetic activity of the molecules to bring it to the intake of the pump.
1.7b The Effects of Condutance
It has been shown that the conductance of a tube is proportional to the cube of its radius and inversely propor-
tional to its length. Therefore it is imperative that the connecting lines be as large in diameter and as short in
length as practical. For best results the diameter of the connecting tube should be at least as large as the
diameter of the pump intake. To avoid a large reduction in pumping speed at the vacuum chamber, it is clear
that the conductance of the line must be considerably greater than the speed of the pump.
1.7c Metal Joints
If metal piping or tubing is used, it is preferable to solder or braze all of the connections. Where threaded joints must be
used, coat the threads with LocTite® Thread Sealant with Teflon®, or Leak Lock and screw together tightly. Flanged
connections with elastomer gaskets make excellent demountable joints. Modular vacuum piping and fittings are now
extensively used.
1.7d Rubber Tubing Joints
Where metal tubing is used between the system and the pump intake, joints can be make by butting the ends of the two
sections together in a short section of vacuum hose.Worm-screw band clamps are useful for securing the hose to the
tubing.Whatever the joint you choose to use, cleanliness should be of utmost importance.
1.7e Valves and Stopcocks
Metal valves or stopcocks may be used in the connecting line between the system and the pump to provide a means of
isolating the pump from the system. To minimize the impedance of flow, the valve openings should be as large as possible.
Lubricate the rotating plug of the stopcock with a film of vacuum grease sufficiently thick enough to prevent seizure.
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