Modifications eliminate contaminant substances from pump fluid during operation, which are principal causes of torpidity on evaporative surface. Diffusion pump is also acting as still. Resulting 100 percent vigorous working surface provides much greater molecular throughput and greatly improved efficiency

Buggele, A. E.

English

NASA Technical Reports Server

July 1975
	
B75-10065 
NASA TECH BRIEF 
Lewis Research Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Diffusion Pump Modification Promotes 
Self-Cleansing and High Efficiency 
Skimming Lines To 
Collection Vessel 
Gutters
Drain Lines To 
Collection Vessel Gutters... —1
Skimming Outlets To 
Collection Vessel 
Drain Outlets 
To Collection 
Vessel 
Fig. 1-B
Skimming 
Outlets 
Foreline
Typical Diffusion 
CD-11763-11
Fig. 1-A 
[1
The Problem: 
Typical large diffusion pump vacuum systems (Figure 
1) have no effective means for removing some contami-
nants absorbed by the vaporizing fluid. These contami-
nants tend to collect on the evaporative surface, thus 
drastically limiting evaporation rates, lowering the pump 
gaseous molecular throughput, and significantly reducing 
efficiency and attainable vacuum by 1½ to 2 decades 
(efficiency varies with the type of pump fluid used). 
Other related problems are: 
(1) Low evaporative rates evident from the quiescent 
(torpid) evaporative surface of the pump fluid. This 
torpidity phenomenon is caused almost entirely by 
"heavy end" contaminant substances of higher molecular
weight than the pump fluid. These "heavy ends" include, 
to a large extent, polymerized molecules of lighter 
substances. These contaminants tend to collect into 
nonevaporating "islands" on the evaporative surface, thus 
restraining the release of fluid molecules in these areas. 
Only the working "holes" in the evaporative surface 
release fluid molecules at an appreciable rate. 
(2) Some lighter contaminant molecules migrate from 
the pump jets back into the vacuum chamber. As pressure 
in the chamber being evacuated decreases, the rate of 
backstreaming increases. When it equals the throughput of 
gas, no further decrease in chamber pressure can occur. 
(3) Although cryogenically cooled baffles between the 
vacuum chamber and the diffusion pump have been 
(continued overleaf) 
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helpful in trapping chamber gases and reducing back-
streaming, they have not been able to trap all passing 
gases. Once they are filled with condensate, they lose their 
effectiveness. Baffle warmup causes these impurities either 
to revaporize or to drip into the pump boiler where they 
cannot be removed. 
The Solution: 
Modify all vapor-operated vacuum diffusion pumps 
into self-cleansing devices by: 
(1) Adding skimming outlets (Figure IA) in the boiler 
for periodically skimming the evaporative surface of the 
working fluid. 
(2) Adding a series of peripheral gutters in the foreline 
(Figure lB) for trapping, separating and draining off 
condensates. 
(3) Providing gutters in the pump barrel (Figure 1C) 
for further removal of trace quantities of residual volatile 
impurities. 
How It's Done: 
These modifications eliminate contaminant substances 
from the pump fluid during operation, which are the 
principal causes of torpidity on the evaporative surface. 
Thus, the diffusion pump is also acting as a still. The 
resulting 100% vigorous working surface provides a much 
greater molecular throughput and greatly improved 
efficiency (15 to 200 times). 
Most heavy ends are eliminated by the periodic 
skimming of the evaporative surface of the pump fluid in 
the boiler during operation. Skimming outlets are located 
around the periphery of the boiler and also toward the 
center of the boiler in large pumps having concentric 
annular boiler channels. The skimming openings are 
provided at various levels in the boiler and are connected 
by valved lines to a collection vessel of lower internal 
pressure than the boiler. 
Nearly all light ends are eliminated by withdrawing 
condensed distillate from the pump foreline. Gutters 
installed in the foreline for condensing and enriching the 
condensates flowing down the internal walls are con-
nected by valved lines to a collection vessel of lower 
internal pressure than the foreline. The periodic removal 
of these condensates that contain high concentrations of 
light-end substances prevents their return to the boiler by 
revaporization and possible polymerization into heavy-end 
molecules. In this way, backstreaming is nearly elimi-
nated, and the overall quantities of impurities are signifi-
cantly lessened. 
Trace quantities of heavy and light ends present in the 
diffusion pump barrel are removed by gutters, drain lines, 
and collection vessels similar to those installed in the 
foreline.
Thus, the entire process permits the self-cleansing of 
diffusion pump liquid, provides for a more efficient 
pump, and permits the reuse of costly diffusion pump oils 
without removal to a separate source for cleansing. 
The research leading to the preceding findings was 
conducted with a series of experimental scale-model glass 
diffusion pump vacuum systems. Investigations to incor-
porate these findings in full size systems appear desirable. 
Notes: 
1. This innovation may also be of value to those technical 
disciplines relating to: (a) chemical processing or 
reprocessing; (b) the removal of contaminants in 
materials used in biomedical applications; and (c) 
separation of impurities from metals. 
2. Further information is available in the following 
report: 
NASA TM-X-2932 (N75-18278), Better Vacuum 
by Removal of Diffusion Pump Oil Contaminants 
Copies may be obtained at cost from: 
Aerospace Research Applications Center 
Indiana University 
400 East Seventh Street 
Bloomington, Indiana 47401 
Telephone: 812-337-7833 
Reference: B75-10065 
3. Specific technical questions may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B75-10065 
4. A film, "Better Vacuum by Removal of Diffusion 
Pump Oil Contaminants," describes in more detail this 
vacuum technology and is available for a no-charge 
two-week loan from the Technology Utilization 
Officer, Lewis Research Center (address above). 
Patent Status: 
This is the invention of a NASA employee, and a 
patent application has been filed. Inquiries concerning 
license for its commercial development may be addressed 
to the inventor: Mr. Alvin E. Buggele, Mall Stop 301-1, 
NASA Lewis Research Center, 21000 Brookpark Road, 
Cleveland, Ohio 44135.
Source: Alvin E. Buggele 
Lewis Research Center
(LEW-12323)
0- 
S 
n 
B75-10065	 Category 06


Diffusion pump modification promotes self-cleansing and high efficiency

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