·
What should the optimum temperature be set in diffusion pump
heaters so as to get maximum level of vacuum in shortest possible time?
·
How can the temperature in diffusion pumps be set in such a
way that the engineers are able to get maximum life from costly diffusion pump
oil?
·
Is boiling temperature of silicone diffusion pump oil
different from hydrocarbon diffusion pump oil?
Before attempting
to understand optimum boiling temperature of diffusion pump oil, let us take a
brief look about working of diffusion pump.
Since efficiency of
diffusion pump depends solely on the working cycle of diffusion pump oil
(diffusion pump has no moving parts) so this is evident that a higher diffusion
pump temperature will mean a higher ultimate vacuum. Obviously a question comes
to mind at this stage that why don’t we increase the boiling temperature to
highest possible level. Answer to this is that increasing the temperature of
diffusion pump oil involves financial implications (cost increase) because of
the following reasons -
1. Diffusion pump oil
works in very difficult environment where there is vacuum and high temperature.
So to increase the boiling temperature, superior (obviously costlier) oil will
be required which is capable of withstanding these adverse conditions.
2. At higher
temperature O-rings and oil seals may give way so better quality sealing
material is required (Costly again).
3. For handling higher
temperature, construction of diffusion pump also has to be stronger.
4. For attaining
higher temperature higher energy charges will be incurred.
5. For obtaining
higher temperature longer time is required so vacuum time increases.
Decision about
boiling temperature is basically a balance between level of vacuum required and
cost incurred. Our guideline in line with the established practice in the industry
is as below -
S. No.
|
Vacuum Required
|
Temperature in Diffusion Pump
|
Supervac Products
|
Equivalent Products
|
1.
|
10-9
to 10-10 Torr
|
245oC
|
SV-SIGMA+
|
DC-705
|
Hivac
F5
|
||||
2.
|
10-7
to 10-8 Torr
|
220oC
|
SV-SIGMA
|
DC-704
|
CVC4
|
||||
Hivac
F4
|
||||
Ulvoil
D31
|
||||
3.
|
10-5
to 10-6 Torr
|
180oC
|
SV-SIGMA
FAST
|
DC-702
|
Some myths are prevalent in the industry about
diffusion pump oils. These are clarified as under-
Myth no.1: Boiling
temperature of hydrocarbon diffusion pump oil is different from boiling
temperature of silicone diffusion pump oil- This myth is
baseless as boiling temperature of both hydrocarbon and silicone diffusion pump
oil is same. For example- Well known hydrocarbon diffusion pump oils like Supervac
SV-DELTA, Lion S, Ulvoil D11 and CVP300, all have boiling temperature of 220oC.
Myth no.2: My
diffusion pump has been designed for hydrocarbon/silicone diffusion pump oil
only- This is also false. You can use any diffusion pump oil
(hydrocarbon or silicone) in any diffusion pump based on your requirement. For
details about merits of hydrocarbon and silicone diffusion pump oil please read
my blog post-http://supervacindustries.blogspot.in/2013/04/silicone-diffusion-pump-oil-vs.html
Myth no.3: My
equipment manufacturer asks me to use only a particular brand of diffusion pump
oil which is exorbitantly priced- Your equipment manufacturer is trying to
fleece you. For details about equivalent vacuum oils manufactured by reputed
and established manufacturers anywhere in the world please read our blog post
at- http://supervacindustries.blogspot.in/2014/03/vacuum-oil-equivalents.html. In case you don’t
find it there then please contact us. We will help you find an equivalent product.
Myth no.4: There
is no need of topping up- Absolutely false and dangerous myth
prevailing in the industry. Topping up at regular intervals is of utmost
importance to get proper vacuum and avoiding damage to the equipment.
Myth no.5: Charging
less diffusion pump oil in diffusion pump reduces vacuum time- Absolutely false.
Charging less oil than required will cause back streaming, burning of diffusion
pump oil and damage to costly equipment.
Myth no.6: My
diffusion pump oil works at 170oC- Diffusion pumps
do not work at temperature below 180oC. Your oil supplier is
supplying you cheaper vapor jet booster pump oil.
Conclusion:-
Based on the
information given above I am sure that you will be able to choose the right
diffusion pump oil as per your requirement. For example- if level of vacuum
required is only up to 10-5 Torr and equipment is old then
hydrocarbon diffusion pump oil will work more economical. Similarly if vacuum
level required is 10-7 Torr then there is no point in using SV-SIGMA+. Furthermore by
using simple precautions like frequent topping up you can get a much longer
life and value for money from your diffusion pump oil.
For more helpful tips
about how to get your money’s worth from your diffusion pump oil, you can read my blog post- http://supervacindustries.blogspot.in/2013/09/how-to-get-maximum-life-from-your.html
