Engineers working in the field of vacuum coating technology, often send us queries regarding vacuum pumps and oils. Rotary vacuum pumps are seemingly small but highly critical in the functioning of the entire vacuum coating process. The same goes for vacuum pump oils as well. In this article, Supervac answers top 20 questions about rotary pumps and oils posed to them.

1. Top 20 Questions about Rotary Vacuum Pumps and Oils
Q.1 What is a Roughing Pump?
Oil Sealed Rotary Vacuum Pump
Ans. A Roughing Pump is nothing but an ordinary Rotary vacuum pump which is
used to evacuate the vacuum system. It is also known as Mechanical vacuum
pump as well as Vane pump. Depending upon the vacuum level desired, it is
used either independently (for low vacuum level) or behind a Booster pump or a
Diffusion pump (for high or ultra high vacuum level) as a Backing pump.
Q.2 What should be the basic properties of rotary vacuum pump oil?
Ans. Rotary vacuum pump oil must have following properties:1. Low vapor pressure of less than 1x10-3 Torr.
2. Should have viscosity between 65 to 80 cst at 40oC.
3. Should not contain corrosive elements like sulphur.
4. Should be resistant to oxidation.

2. 5. Viscosity of the oil should not change much with change of temperature.
Q.3 Which is better - synthetic rotary vacuum pump oil or mineral vacuum pump
oil?
Ans. Synthetic rotary vacuum pump oils give higher vacuum, create vacuum
faster and have longer working life. In addition, synthetic rotary vacuum pump
oil preserves and protects the pump interiors. So these next generation synthetic
oils are superior to commonly used organic rotary vacuum pump oils. The latter
is used only where cost is an issue. Supervac Industries manufactures both
synthetic as well as mineral rotary vacuum pump oils – SV-77 and SV-68
respectively.
Q.4 Can I use simple hydraulic oil for my rotary vacuum pump in place of rotary
vacuum pump oil?
Ans. No, you should never do that as this can seriously damage your rotary
pump. Rotary vacuum pump oil is not an ordinary lubricant. It is a special fluid
manufactured with thermal and oxidative stability. Unlike hydraulic oil, rotary
vacuum pump oil has a low vapor pressure. It is therefore absolutely different
from normal hydraulic oil or motor oil.
Q.5 Can I use simple motor/engine oil for my Rotary Vacuum Pump?

3. Ans. Never ever use motor/engine oil for your Rotary vacuum pump. People tend
to make this mistake so very often only to end up regretting eventually. Motor
oils are lubricants designed for automobile engines which work under different
principles whereas rotary vacuum pump oils are specialty fluids manufactured
keeping in mind the requirements of a vacuum pump. Motor oils have a different
viscosity from vacuum pump oils and have no vacuum properties at all. Motor
oils carry various additives like rust inhibitors and anti-corrosion compounds.
When put in the rotary pump, under low pressure and high temperature, these
additives separate from the base fluid and cling to the insides of the pump as
sticky/gummy solids. This affects the vacuum pressure and harms the pump.
Under high temperature of the vacuum pump, motor oils/hydraulic oils start
releasing vapors, thus bringing down the vacuum, where as good quality rotary
vacuum pump oils do not release any vapors. Supervac manufactures high
quality Synthetic Rotary Vacuum Pump Fluid- SV-77, which is a boon in terms of
vacuum formation and pump maintenance.
Q.6 Do Roughing/rotary pumps need topping up of vacuum pump oil?
Ans. Rotary vacuum pumps lose a small amount of vacuum oil in the form of oil
mist. This loss is pronounced in initial (roughing) phase. To make up for this loss
of oil it is advisable to top up rotary vacuum pump oil from time to time.
Q.7 Will Rotary vacuum pump oil used in Kinney pump and Stroke pump ( both
are roughing pumps) be the same or different?
Ans. Vacuum pumps as well as vacuum pump oils are made as per
international specifications. So a good rotary vacuum pump oil will be suitable
for all/any rotary vacuum pump made anywhere in the world and by any
manufacturer.

4. Just like the same petrol works for cars made by Honda, Suzuki, Audi, Toyota or
any other brand.
Q.8 What is a two stage rotary vacuum pump?
Ans. A Rotary vacuum pump works by mechanically compressing and pushing
out the air from inlet to outlet. The outlet pressure therefore has to be higher
than atmospheric pressure for exhaust to take place. In two stages rotary pump
the outlet of one chamber is connected to inlet of next chamber. This increases
the compression and makes the air exhaust possible.
Majority of rotary pumps are two stage rotary pumps.
Q.9 How do I know that I need to change the oil of my rotary pump?
Ans. In vacuum industry practices for vacuum oil change vary widely.
Usually one of these three reasons trigger oil change:1.
Rotary pump starts taking longer to create vacuum or is unable to reach the desired
vacuum level.
2. Color of oil changes from transparent or golden yellow to dark brown indicating
oxidation.
3. Some engineers prefer to change oil after a fixed number of working hour which are
either recommended by manufacturer or are based on experience.
Q.10 Can I recycle my rotary vacuum pump oil?
Ans. No, rotary vacuum pump oil cannot be recycled. This is because vacuum
pump oils work under very demanding conditions. Used vacuum oil, even if
recycled, will still be carrying various contaminants. For the safety of expensive
vacuum pump, used oil is best discarded.
Q.11 What are the reasons of noise in rotary vacuum pump?
Ans. Normally rotary pumps work noiselessly.
Noise in rotary vacuum pump could be because of following reasons:1.
Excessive gas load because of some leak in system. This may also be
accompanied be release of oil mist from pump.
2. Some foreign object lodged in rotary pump. This will cause intermittent,
loud noise.
3. Worn out ball bearings. This causes continuous noise.
Q.12 What is the normal working temperature of a rotary vacuum pump?
Ans. Normal working temperature of rotary pump is about 80o C.

5. Q.13 My rotary pump overheats sometimes. Is this serious?
Ans. Yes, this is serious as pump can get seriously damaged if temperature of
pump exceeds 100oC. Rotary pumps need to be run in well-ventilated areas and
in case of extremely hot climates, as is common in India, use a fan to cool the
pump externally. Overheated pumps will not give the required vacuum and thus
unduly affect either the working of diffusion pump or the entire process. Also,
the oil in an overheated pump will turn less viscous (too thin) and will not
lubricate the pump interiors well; thereby leading to pump failure.
Q.14 What is gas ballast in rotary vacuum pump?
Ans. Since rotary vacuum pump creates vacuum by positive displacement and
compression of air so during operation of this pump some water vapors
condense to water and mix with vacuum oil. This reduces the vacuum.
Some pumps are equipped with gas ballast mechanism. This mechanism allows
some air to flow into compression portion of pump cycle, diluting the water
vapor. This causes fewer tendencies of water vapors to condense. This is called
gas ballasting.
Q.15 Do vane type rotary pump and piston type rotary pump require different
rotary vacuum pump oils?
Ans. In both vane type rotary pump and piston type rotary pumps, function of
vacuum oil is to provide lubrication. At the same time for both these pumps the
rotary vacuum pump oil should have a low vapor pressure and good viscosity
stability.
Since both types of pumps require same characteristics of vacuum oil so the
same vacuum oil is used for both these types of pumps.
Q.16 How do piston pumps work?

6. Piston Rotary Vacuum Pump
Ans. Piston pump is a type of Rotary Vacuum Pump. This pump works on a
principle of drawing in and compressing of gas to exhaust it to atmosphere. It
has an eccentric circular piston that rotates around the cylinder to create
vacuum. This pump requires a Rotary Vacuum pump oil seal between the metal
surfaces of the piston to separate the incoming and exhausting gas in the pump.
The circular piston, rotating around the pump sucks in air from the chamber,
compresses it and drives it out from the pump to create vacuum. Rotary Vacuum
Pump oil provides lubrication also.
Q.17 What is a dry rotary vacuum pump. Compared to oil-sealed pump, is it
economical to use?

7. Dry rotary vacuum pump
Ans. A dry pump does not depend on Rotary Vacuum Pump Oil for its operation.
In this pump a set of spirals draw air in to the center of spiral, continuously
compressing it. Air thus compressed finally exits from the center of spiral. These
spirals are normally made of Ceramic materials.
Because of very high cost this pump is not very popular in vacuum industry and
is used only where oil free vacuum is essential.
Q.18 Oil rotary vacuum pump or dry vacuum pump - Which works out cheaper?
Ans. A conventional rotary vacuum pump using rotary vacuum pump oil works
out cheaper. Dry pump have a very high cost because of ceramic components
used in them. Dry pumps are mainly used in industries like semi conductor
industry where cost is not of much importance.
Q.19 What is Holding Pump?

8. Holding vacuum pump
Ans. Holding pump is a simple rotary vacuum pump of small capacity. Its
function is to create holding vacuum for diffusion pump, hence the name holding
pump. It is invariably connected to diffusion pump and not directly to the vacuum
chamber.
Q.20 Why should I buy rotary vacuum pump oil from Supervac Industries?
Ans. Supervac Industries, New Delhi, India is a reputed and trusted supplier of
Rotary Vacuum pump oil. More than 90% of companies using vacuum systems
in India are buying vacuum consumables from Supervac Industries for more
than 15 years.