Welch DUOSEAL 1399B-01, Owner'S Manual

5

1.15 

Electrical Power

1.151  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.  

1.152  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.

1.16 

Vacuum Connections (See Accessory Section in back of this manual.)

1.161  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.

1.162  The Effects of Conductance

It has been shown that the conductance of a tube is proportional to the cube of its radius and inversely 

proportional 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.

1.163  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.

1.164  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.

1.165  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.

CAUTION

Make certain the power settings on the pump match your power

source before attempting to operate the pump