Roots Blower Booster Vacuum Pump Oil

 



Roots Blower Booster Pumps

                                                                                          

Roots Blower Booster Pump:

These pumps work on the principle of positive displacement of gas. The Roots pump consists of two impellers called roots in the shape of figure 8. These impellers are mounted on parallel shafts in a single cylinder having inlet and outlet openings on the sides. The impellers, through synchronized rotative timing, are maintained in a relative position to each other and rotated in opposite directions without any internal contact and at a very high speed measuring a couple thousand or more rpm. The operating clearances are very small, measuring just a few microns– only a few thousandths of an inch - in order to keep back leakage to a minimum.

The following diagram shows how the rotation of impellers traps and pushes the gas/air out. The positive displacement works in a continuous flow to create vacuum.

 

Choose the Right Type of Lubricant

 

Often, out of ignorance, cost-cutting or any other reason, people use ordinary machine oil, automotive lubricants, gear oils or even normal rotary pump oil in these booster pumps. Since these oils do not have properties required for safe running of Booster Pumps, this leads to serious damage to the pump. Repairing a booster pump is nearly impossible without a complete overhaul which costs a lot while a new pump too costs lakhs of rupees. Choosing the right lubricant for the booster pump is the best type of insurance one can bank upon. A suitable, high quality booster pump oil is the pump’s primary protection against wear, pitting, spalling, scoring and scuffing of moving metal parts. The following pictures demonstrate the type of damage that can occur due to –

1.   Wrong choice of lubricant

2.   Not topping up at the right time, so the metal parts are not well-oiled.

 

 

 

 

 

 

 

Careful selection of lubricant goes a long way in saving the machinery thereby preventing loss of time and money.

When it comes to choice of lubricant – One size DOES NOT fit all 

Different vacuum processes require different types and grades of vacuum oil.

Supervac Roots Blower Vacuum Lubricants:

After careful actual testing on Roots blower pumps, Supervac has formulated Roots blower vacuum oil in two grades-

1.   Hydro-carbon based booster pump oil- SV-90H

 

 

2.   Silicone based booster pump oil- SV-90S

Both are suitable for all makes and sizes of Roots Booster pumps all over the world.

Specifications:

SV-90H (Hydrocarbon)		SV-90S (Silicone)
Property	Value	Property	Value
Vapor Pressure at 250C	Below 1x10-4 Torr	Vapor Pressure at 250C	Below 1x10-4 Torr
Flash Point	2700 C	Flash Point	3000 C
Viscosity at 400 C	90 cst	Viscosity at 400 C	90 cst
Pour Point	Below (-) 100 C	Pour Point	Below (-) 150 C
Appearance	Pale Yellow	Appearance	Water White
Packaging	(20 Ltrs.) (210 Ltrs.)	Packaging	(20 Ltrs.) (210 Ltrs.)
Equivalent	Edwards Stokes- V lube Grade H oil Lubricant	Equivalent	Roots Synthetic Lubricant ISO VG 320 LVO 210 GS 555 HE 600

• Supervac Roots Blower vacuum pump oils have the following properties- 

1. Excellent lubrication

2. Heat dissipation

3. Protection of the pump machinery

• It carries damaging wear debris away from contact zones.

• Offer extreme temperature and pressure protection in order to prevent wear, pitting, spalling, scoring, scuffing and other types of damage that result in equipment failure and downtime.

• Protection against-

1. Oxidation

2. Thermal degradation

3. Rust

4. Copper corrosion and

5. Foaming.

Pump parts come in contact with different types of contaminants like water, corrosive chemicals and surface wear debris which can cause serious and irreparable equipment failure.

 

What is special about Supervac Roots Blower Vacuum Pump Oils?

Supervac Roots Blower lubricants have been formulated specially for Roots Booster vacuum pumps (also called positive displacement pumps) and are loaded with the following features –

• Viscosity index improvers – Supervac brand Roots Blower pump oils have the viscosity - 90 cst at 40⁰ C which is ideal for functioning of the pump. Special viscosity index improver additives make them work superbly in hot as well as cold climates.

• Anti-foam additives –Impellers inside the pump are moved by gears at a very high speed (2000 or more rpm) and oil on them is churning at that point. Ordinary gear oil is likely to form foam. Formation of foam in Roots Blower pump is absolutely unwanted in a vacuum system. Just a trace amount escaping into the chamber can wreak havoc to the entire process. Supervac Roots Blower oils have been specially formulated keeping this important property in mind.

• Wear protection additives – Along with lubrication, Supervac Roots Blower oils protect the machinery against wear like pitting, spalling and scuffing thereby enhancing the machinery life.

• Corrosion inhibitors – Special additives in these oils resist corrosion caused by strong toxic process gasses.

• Extremely high film strength

• Low co-efficient of friction

Warning:

1)   Supervac DOES NOT recommend the use of automotive lubricants or gear oils for Roots Blower pumps as they DO NOT have the above mentioned properties which are absolutely necessary for vacuum booster pumps.

2)   Topping up of Booster Pump oil is absolutely essential to prevent pump damage. If level of oil falls below required level, immediately make up the level by adding more oil.

 



 

As is evident from the above diagram, a whopping 89% of the problems related with booster pumps are lubricant related. Merely choosing a good pump is not enough. If money’s worth is to be taken out of that pump then it has to be run with the right oil and regular and timely topping up ensured.

 

 

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Why is Cleaning of Vacuum Chamber Required?

Vacuum Chambers

It is but natural that during the process, material being coated on substrate will fall off in the vacuum chamber. For example, Aluminum heated and evaporated to be coated on BOPP film (film metallizing) or on some object (object metallizing) will fall off on vacuum chamber and shields. Being in molten state this will weld to the chamber surface. (PHOTO-1)

Metallizing in the Vacuum Chamber (Photo-1) 

After a number of work cycles there will be a buildup of this welded metal which will have large gaps capable of trapping a lot of air (PHOTO-2).

 

Photo-2

As it is evident the porosity holding air will be zigzag as it has been formed randomly. Pumping system will find it very difficult to remove this trapped air. Hence ultimate vacuum will drop and vacuum time will increase. It is important therefore that this build up of molten metal is removed from time to time so that trapped air inside vacuum chamber remains to minimum level.

Naturally a question comes to mind that why don’t plant manufacturers provide shields all around the target so that the extra metal dropping and welding to vacuum chamber is eliminated. The problem is that excessive shielding will in itself become an air trap and will result in what is called a virtual leak (details at http://supervacoils.com/leakage-detection-and-prevention-in-vacuum-systems/). This virtual leak itself is capable of slowing down the vacuum time considerably. Therefore this is impractical.

Production engineers therefore are left with no choice but to clean the vacuum chamber periodically.

Various means of achieving this cleaning are discussed below----------------------

1.    Boron Nitride Suspension: -

In this method Boron Nitride Suspension/Paste is applied in vacuum chamber on parts where stray metal can fall. Boron Nitride Suspension adheres to applied surface and forms a protective coating. This coating acts as a physical barrier and prevents welding of stray metal to vacuum chamber. At the time of cleaning it is very easy to remove stray metal that has fallen in the chamber; it is just swept off!

Alternatively some users mix Boron Nitride Powder with water and then apply it to the required surface.

Advantages: - Advantage of Boron Nitride Suspension/Paste is that it is easy to use, neat in use, has very good lubricity and is therefore very effective (Fig.- a). It has good adhesion properties so it easily sticks to the applied surface. Boron Nitride Suspension is also inert and is very easy to remove (normally removed with a wet cloth Fig.- b).

 

Disadvantages: - Boron Nitride Suspension is expensive and mildly hygroscopic which causes it to absorb moisture.

2.    Graphite Suspension: -

Application of graphite suspension/paste is very similar to BN suspension/paste. In this method Graphite Suspension/Paste is applied in vacuum chamber on parts where stray metal can fall. Just like BN suspension, it adheres to the applied surface and forms a protective coating. This coating acts as a physical barrier and prevents welding of stray metal to the vacuum chamber. At the time of cleaning it is very easy to remove the stray metal that has fallen in the chamber, it is just swept off!

Advantages:- Advantage of Graphite Suspension are that it is easy to use, has very good lubricity and is therefore very effective; has good an adhesion properties so it easily sticks to the applied surface (Fig.-c). Graphite Suspension is inexpensive and is very easy to remove (normally removed with a wet cloth Fig.-d).

 

Disadvantages: - Graphite Suspension/Paste is somewhat messy to use and mildly hygroscopic which causes it to absorb moisture.

3.   Caustic Soda (NaOH):-

In this method, after vacuum is broken, the chamber is opened and Aqueous Caustic soda is applied to remove deposited Aluminum. Caustic soda reacts with aluminum and therefore removes it from chamber surface by chemical reaction.

2Al + 2NaOH + 2H₂O ------------> 2NaAlO₂ + 3H₂

Advantages: - Main advantage of caustic soda is that it is applied after operation is over and machine is idle. So it does not interfere in the vacuum process.

Disadvantages: - Caustic soda is polluting and a very hazardous chemical and needs to be handled very carefully.

 

Reaction of aluminum with caustic soda is exothermic and produces a lot of heat. Cleaning with caustic soda requires chemical reaction so it is slow. Cost of cleaning is also high as special facility needs to be created to store and dispose of caustic soda.

4.  Removing by Abrasives: -

 

In this method, a small hand held grinding machine is employed to remove deposited metal by abrasion. Care must be exercised to polish/ buff the ground surface afterwards otherwise rough edges can trap air and moisture.  

Advantages: - Main advantage of this process is that it is applied after operation is over and machine is idle. So it does not interfere in the vacuum process.

Disadvantages: - Disadvantages are many. Fine abrasive particles fly during the process and can contaminate the chamber. This process is time consuming and requires expertise on the part of operator. Excessive grinding because of repetitive use can weaken the walls of chamber and cause vacuum leakages. Also it is impossible to be able to remove deposited metal cleanly with this process.

5.  Hammer and chisel method: - 

 

Crudest of all methods, can damage plant in a matter of days. Must not be attempted.

Conclusion

In my opinion, application of Boron Nitride Suspension/Paste continues to be the most effective and practical way of keeping the vacuum chamber clean of the deposited metal. If cost is a major consideration, for example, if the surface to be protected is very large then Graphite Suspension/Paste can be used as the next best thing. For comparison between Boron Nitride Suspension and Graphite Suspension detailed blog on the subject http://supervacoils.com/graphite-suspension-vs-boron-nitride-suspension/ can be read.

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Written by: Anshuman Punj.   

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