WELCH-ILMVAC DUOSEAL 1405B-01, Owner'S Manual

6

1.17 

Traps (See Accessory section in the back of this manual.)

1.171  The need for a Trap
 

Where corrosive vapors or large quantities of condensable vapors are evolved from vacuum processing, a cold 
trap may be used in the connecting line to the pump.  It will help prevent damage to the pump mechanism and 
reduce oil contamination.  The cold trap, immersed in a suitable Dewar fl ask, is installed to that the vapors may 
come in contact with the surfaces of the trap and condense.  Commonly used refrigerants are liquid nitrogen or 
dry ice and acetone.  The refrigerant to be used depends upon the freezing point of the contaminations.  A variety 
of cold traps are available from Welch-Ilmvac.

1.172  The care of a Trap
 

When using a cold trap the refrigerant should be maintained at a high level in the fl ask to keep the trap at a 
uniformly low temperature.  If the trap is re-warmed it may allow re-evaporation of the condensate.  The refrigerant 
add tube on the liquid nitrogen trap should not be obstructed as the refrigerant boil-off can produce dangerously 
high pressures.  If the trap becomes saturated it should be disconnected from the system, drained and cleaned.  
An increase in pressure in the vacuum system will normally indicate that the trap has become saturated. To clean 
the trap, remove the trap from the system, allow the trap to warm up and rinse off the condensate with a suitable 
solvent in a fume hood.  Thoroughly clean and dry the trap before reinstalling in the system.

Section 2: OPERATION

2.10 Starting 

Procedures

2.101  Starting a DUOSEAL Pump
 

Before attaching the pump to a system it is well to familiarize yourself with the function and action of the pump 
which you have now required.  Remove the intake and exhaust port plugs and temporarily provide a stopper for 
the intake and a dust cap for the exhaust.  Review the power requirements as described in Section 1.4.

CAUTION

Do not run this pump with the intake open directly to the 

atmosphere.  The pump will overheat, excessive oil mist will be 

emitted from the exhaust and the pump will eventually seize.

2.103 Cleanliness
 

Take every precaution to prevent foreign from entering the pump.  A fi ne mesh screen is provided for this purpose 
in the intake passage of all DUOSEAL pumps.

2.104  Oil Level Determination
 

The amount of oil suitable for effi cient and satisfactory performance should be determined after the pump has 
reached its operating temperature.  Initially, however, the pump should be fi lled with fresh oil while the pump is 
idle.  Fill the pump until the oil level falls half way of the oil level window.  If after a short period of operation the 
level should fall, it is likely the result of oil entering some of the interior pockets of the pump.  If the oil level rises, 
this signifi es oil has drained into the pump cavity while pump was idle.  Shut off pump, then drain oil down to 
proper level.

If a gurgling sound occurs, additional oil must be added.  Mechanical pumps will gurgle in varying degrees under 
four conditions of performance: [a] when operating at high pressure as in the beginning cycles of evacuation of a 
chamber; [b] when the oil level in the pump reservoir is lower than required; [c] when a large leak is present in the 
system; and [d] when the gas ballast is open.  Awareness of the possibilities will save time in setting up a system.  
Best performance of a mechanical pump is generally obtained after suffi cient time has been allowed for the pump 
to come to operating temperature.