Welch Vacuum 1376N Chemstar - Manual (Page 24)

24
WARNING
DIRECTORR Gold Oil is not inert and should not be used in environments
involving a high percentage of oxygen. The use of DIRECTORR Gold Oil for
pumping a high percentage of oxygen can lead to a pump fi re and injury to
personnel.
CAUTION
Failure to use Fomblin Y06/6 in applications where strong acids, halogens or
ozone exceed recommended gas fl ow limits given will lead to degradation of
the DIRECTORR Gold Oil and to the CHEMSTAR pump failing.
If the fl ow of strong acids or halogens exceeds 10% of gas fl ow, you must switch to a perfl uoropolyethers such as
Fomblin Y06/6 (Welch Cat. Nos. 1408C-06, 1 Kg; 1408C-08, 2Kg) - Fomblin is a registered trademark of Ausimont. In
addition, if ozone is pumped and its concentration exceeds 100 ppm of the gas fl ow, a perfl uoropolyether oil must be
used. Perfl uoropolyethers are very resistant to chemical attach by strong acids.
B. Connecting your CHEMSTAR Pump to the Vacuum System
The choice of connections and fi ttings can have a very marked effect on the pumping speed at the vacuum chamber. Any
connection placed between the pump and the chamber creates and impedance to the fl ow of gas. This is particularly
true at low pressures in the millitorr range where the gas fl ow is substantially molecular in character. The gas fl ow is then
dependent upon the kinetic activity of the molecules to bring it to the intake of the pump.
It has been shown that the conductance of a tube is proportional to the cube of its diameter and inversely proportional to
its length. Thus, it is critical 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. The conductance of the line must be greater than the speed of
the pump.
C. Types of Accessories Available for Your CHEMSTAR Pump
Protective accessories may be needed for heavy corrosive gas loads which may contain particulates. In Section 5,
recommendations are given which detail when these accessories should be used. Below is a description of these
accessories and how they work.
C 1. Acid Neutralization Trap
The acid neutralization trap features a transparent sump which contains an element which neutralizes hydrous acids. The
element consists of alkaline material contained within stainless steel end caps and screens.
The trap comes in two sizes. Cat No. 1420H-21 uses a 4.5 inch deep sump and is used with CHEMSTAR Model 1400N-
01. Cat. No. 1420H-20 uses a 9.5 inch deep sump and is used with CHEMSTAR Models 1402N-01, 1376N-01, and
1374N-01.
Acid neutralization traps are used in applications where the ultimate pressure required is greater than 0.01 Torr (10
microns of Hg). The acid neutralization trap somewhat limits the achievable ultimate pressure and pumping speed of the
CHEMSTAR pump. The ultimate pressure limitation is brought on by the degassing characteristics of the element. The
pumping speed is limited since the trap will provide resistance to gas fl ow (See section II.B.)
The white alkaline material making up the element turns a bluish-purple when spent. The color change is visible due to
the transparent nature of the sump containing it.
If water vapor is evolved from your applications, such as in freeze drying, Welch recommends a cold trap be placed
between the vacuum chamber and the acid neutralization trap. The cold trap will knock out the water vapor and prevent it
from saturating the acid neutralization trap’s alkaline element.
CAUTION
When pumping heavy water vapor loads, failure to place a cold trap between
the vacuum chamber and the acid neutralization will lead to rapidly saturated
element and reduced effectiveness of the acid neutralization trap.