How To Get Maximum Life From Your Diffusion Pump Oil

Diffusion Pump Oil is one of the costliest consumables required by vacuum users. In the present day scenario of cut throat competition, engineers are under a lot of pressure to reduce costs without compromising on quality. Based on my experience of almost 20 years in the vacuum line, I have compiled a list of do's and don'ts as to how one can get maximum life from the diffusion pump oil. For the benefit of our valued customers, the facts are given below -

1.   Topping up at regular intervals is most important factor in getting maximum life from Diffusion Pump Oil. Care should be taken to top up the oil in the pump in a timely manner. In the absence of topping up, volume of oil in the Diffusion Pump reduces, whereas heaters keep producing the same amount of heat. This causes overheating and accelerated loss of DP oil. This further reduces the volume of oil, which in turn causes more overheating and loss of DP oil is further accelerated and so on.

Diagram of Diffusion Pump

2.   Keep track of the water flow through the cooling lines. Check the inlet and outlet water temperature as well as the flow rate. Lines can become clogged or scaled over time. As Diffusion Pump oil vapor can only condense on coming in contact with cold walls of DP. Any reduction in cooling causes overheating and increase of pressure inside DP. This may result in loss of oil by back streaming.

3.   Strange as it may sound a very low fore- pressure can also cause loss of DP oil. This can be prevented by switching on heaters before fore pressure becomes too low.

4.   Faulty gauges for pressure/heater too, can cause accidental overheating of the oil or the oil not getting the required heating. Check that all the gauges are functioning properly.

5.   Silicone diffusion Pump Oils have a life of about 4 times that of Hydrocarbon Diffusion Pump Oils. Also Silicone Diffusion Pump oil does not blacken and clog the jets of DP so Silicone DP oil works out more economical in the long run.

6.   Poorly working Rotary Pump will put extra burden on diffusion pump. It must be ensured that Rotary pump is working properly to get full life from Diffusion Pump Oil.

7.   Do not expose the oil to air when it is heated. Doing so will affect the viscosity of the oil – it thickens and vacuum reduces. To avoid air exposure valves must be checked from time to time.

8.   To avoid having the oil migrate into the vacuum chamber, a cold cap should be fitted at the top of the nozzle assembly inside the diffusion pump. This cold cap condenses the vapor in that area.

9.   A concentric circular chevron baffle should be present at the mouth of the pump. It allows air molecules to wander in, but traps the heavier oil vapors as they try to escape.

10. There should be no gross vacuum leaks as this will result in deterioration of oil quickly. Vacuum leaks also cause the pressure to drop and in extreme cases may cause stalling of Diffusion Pump. Stalling will cause loss and deterioration of diffusion pump oil. Such leaks can be plugged by applying silicone vacuum grease to O rings and joints.

11. Sometimes back streaming of contaminants from the vacuum chamber takes place causing the oil to form sludge. This is preventable by installing filters above the chevron baffle of the diffusion pump.

12.    Silicone diffusion pump oil starts to decompose if it comes in contact with even trace elements of alkali metals (e.g. hydroxides  of sodium, potassium, cesium etc.). If process requires use of these then care should be exercised to prevent them reaching silicone DP oil. 

13.  In processes like PVD, coatings requiring plasma or transparent metalizing, gas load can cause vacuum of diffusion pump to fall below 10^-1Torr. This can result in back streaming of DP Oil or even stalling. This is preventable by reducing the process speed or increasing the capacity of backing pumps.

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Boron Nitride Powder: SV-BNP+ (Supervac Industries): Properties and FAQs

Q1) What is the particle size of SV-BNP+?

Answer: The average particle size of SV-BNP+ boron nitride powder is 5 micron.

Q2) Is it water soluble?

Answer: Yes, SV-BNP+ can readily dissolve in water to form a smooth lubricious paint-like liquid. Quantity of water can be as per the user’s requirement. Thereafter it can be applied with a paint brush, roller or sprayed.

Q3) Can it be mixed with a solvent?

Answer: Yes, SV-BNP+ can be dissolved in any solvent if so required.

Q4) What is the purity of SV-BNP+?

Answer: SV-BNP+ comes with the purity >99%. This makes it suitable not only for high-precision, high-technology fields, but also for advanced research purposes as well.

Q5) What is the crystal structure of SV-BNP+?

Answer: SV-BNP+ boron nitride powder’s crystal structure is hexagonal.

Q6) We need good quality boron nitride powder for sintering. Can SV-BNP+ withstand high temperatures?

Answer: SV-BNP+ powder can withstand temperatures till 1800 degree centigrade in an inert atmosphere or under vacuum without losing any of its properties.

Q7) We are a thermoplastic compound manufacturer. Is SV-BNP+ suitable for us?

Answer: Absolutely. SV-BNP+ is added to thermoplastic compounds for adding thermal conductivity. SV-BNP+ dissipates heat while retaining electrical insulation properties.

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Boiling Temperature of Diffusion Pump Oil Explained

A lot of confusion exists in the vacuum industry about certain things, for example-

·         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 220^oC.

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 170^oC- Diffusion pumps do not work at temperature below 180^oC. 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

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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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Written by: Anshuman Punj. 

  

 

 

 

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