Monthly Engineering Horizons



September 21
16:52 2020

By: Dr. Suleman Qaiser, National Institute of Vacuum Science & Technology (NINVAST),P.O. Box # 3125, Islamabad


 As the importance of vacuum technology is increasing, the demand of vacuum pumps in the industry is also increasing. In many industrial applications like metalizing, coating, electron beam welding, vacuum furnaces, mass spectrometers, leak detectors etc. required high vacuum in the range of 10-6 -10-8 mbar or higher. This range of vacuum pump can be attained using turbo molecular pumps but these pumps are expensive and their maintenance required sophisticated instruments and expertise. The diffusion pumps are vapor jet pumps that work on the principle of momentum transfer. These pumps are very useful for attaining the high vacuum in the range of 10-6 -10-8 mbar. These pumps are popular in industry due to their low cost and easy maintenance. These pumps are available in a wide range of pumping speed from 180 L/s to 30,000 L/s. In this paper the working principle, design, construction and operation of diffusion pumps has been described in detail.




The use of high and ultrahigh vacuum as a research tool has increased rapidly in recent years. It is essential part of almost all the modern research instruments. Besides its applications in sophisticated research and development, it is vastly applied in the deposition of thin films for micro-miniature electronics and components, simulation of outer space for testing of missiles and satellite components, material research and in various processes of renewable energies. In order to enhance the quality and perfection of these applications, the importance of high vacuum pumps has been realized. The pumps used for the generation of high vacuum includes: diffusion pump, turbo molecular pumps, drag molecular pumps, titanium sublimation pumps, cryo-pumps and sorption pumps. In generally, turbo molecular pumps and drag molecular pumps are expensive, sensitive and difficult to maintain. The titanium sublimation pumps, cryo-pumps and sorption pumps are not suitable for large volumes and their running cost is also high. The  diffusion  pumps  are  vapor  jet  pumps that work on the principle of momentum transfer. These are one of the oldest and the most reliable ways of creating low vacuum, down to 10-10 mbar.


Fig. 1:    View of a water- and air-cooled diffusion pump

This type of pump was first introduced by Wolfgang Gaede in 1915, using mercury vapor    [1-3]. These were the first type of high vacuum pumps operating in the molecular flow regime, where the movement of the gas molecules is better understood as diffusion phenomenon, than by conventional fluid dynamics. Gaede used the name diffusion pump but his design was based on the finding that gas cannot diffuse against the vapor stream, but will be carried with it to the exhaust [4]. Therefore, principle of operation can be more precisely described as gas-jet pump. In modern text books, the diffusion pumps are categorized as a momentum transfer pump.

The diffusion pump is widely used in both industrial and research applications. These pumps are used where throughput for heavy gas loads is important. These pumps begin to work at approximately 10-2 mbar, after a mechanical backing pump has exhausted most of the air in the system. These pumps are very useful for attaining the high vacuum in the range of 10– 6 to 10-8 m bar.  These pumps are popular in industry due to their low cost and easy maintenance. The shape of water cooled and air cooled diffusion pump is shown in Figure 1.


        The diffusion pumps are vapor jet pumps that work on the principle of momentum transfer. The diffusion pumps use a high speed jet of vapor to direct gas molecules in the pump throat down into the bottom of the pump. The oil is gaseous when entering the nozzles. Within the nozzles, the flow changes from laminar, to supersonic and molecular. Often, several jets are used in series to enhance the pumping action. The pump works by heating the pump fluid to its boiling point, thus, producing the vapors.  The vapors travel upward inside the jet assembly and are accelerated out and downward through the jet nozzles toward the cool outer walls of the pump body. The pump body is externally cooled, so that the fluid will condense on its inside surface and run back down into the boiler [2, 3, 5-10]. Pump bodies are typically water-cooled, but some are air-cooled. As the vapor passes the inlet, it picks up elements of the gas to be exhausted and carries them to the ejector. Subsequently, they reach the fore line where they are exhausted to the atmosphere by the mechanical backing pump. The pumping cycle of diffusion pump is illustrated in Figure 2.

         Fig. 2:    Pumping cycle of diffusion pump       

The large diffusion pumps achieve a vacuum, using a five-stage jet assembly, consisting of four diffusion stages and one ejector stage. The oil diffusion pump is operated with an oil of low vapor pressure. Its purpose is to achieve higher vacuum (lower pressure) which cannot be attained by using a positive displacement pump, alone. The operation of a diffusion pump is highlighted in Figure 3. Although, the use of a diffusion pump has been mainly associated with the high-vacuum range (down to 10−9 mbar), but diffusion pumps today can produce pressures approaching 10−10 mbar, when properly used with modern fluids and accessories. The features that make the diffusion pumps attractive, for high and ultra-high vacuum applications are: its high pumping speed and low cost per unit pumping speed, compared with other types of pumps used in the same vacuum range. The diffusion pumps cannot be discharged directly into the atmosphere, so these typically required a mechanical fore pump to maintain the outlet pressure around 0.1 mbar.


There are no moving parts in a diffusion pump. The diffusion pump basically consists of a stainless steel chamber. The chamber has a ring of copper tube for circulation of, cold water. In air cooled pumps copper fins are brazed on the main pumping body. The heart of the pump is a multistage jet assembly. This consists of a group of concentric cylinders that are capped to leave small openings through which vapors can be deflected down and out, toward the pump walls. A cold cap, mounted on top of the jet assembly helps to keep pump fluid vapors out of the evacuation chamber. The pumps are normally water-cooled or air cooled. The vacuum fluid heater is mounted at the bottom of the pump body. The pumps also have a fill and drain assembly, and thermal protection switches. The inlet is at the top, and the exhaust is through the fore line. At the base of the chamber is a pool of a specialized type of low vapor pressure oil. The oil is heated to boiling point by the electric heater [5-12]. The vaporized oil moves upward and is expelled through the jets in the various assemblies. Water circulated through coils on the outside of the chamber cool the chamber to prevent thermal runaway and permit operation over long periods of time. These pumps are available in a wide range of pumping speeds. The construction of a typical diffusion pump is described in Figure 4. The temperature at the base of the chamber, where the oil is being vaporized, ranges from 190°C to about 280°C. As the basic objective of this pump is to create a vacuum by removing gas molecules, so, the surfaces inside the chamber should be very clean during operation. The operators working on these pumps are advised to wear gloves, because even a single finger print can outgas water vapor and other molecules. When a vacuum diffusion pump is slower than normal in pumping down to the desired vacuum level, the reason is likely to be either out gassing of moisture on internal surfaces of plastics or other volatile substances, or a leak. All have the same effect i.e. they add molecules to the atmosphere that the pump is trying to evacuate. When a pump is disassembled for routine maintenance and cleaning, one of the final steps is purging with dry nitrogen. The materials utilized in a typical diffusion pump are presented in Table 1.


The diffusion pumps are available commercially in the pumping speed ranging from a few L/s to several tens of thousands. There is no limit to the vacuum that could theoretically be achieved with a diffusion pump. However, in practice there is a limit to the base pressure that may be obtained with them. This depends on the degree of gas evolution in the vacuum line and the effectiveness with which the working fluid molecules are prevented from diffusing into it. The back-diffusion can be minimized by placing a trap cooled with liquid nitrogen between the diffusion pump and the vacuum manifold. With moderate precautions pressures of 10-6 mbar can be achieved using diffusion pumps and pressures 10-9 – 10-11 mbar, if special attention is paid to the design and    maintenance   of the    vacuum   line.  This includes the selection of materials for the construction, the placement of efficient traps and baffles, as well as the adherence to proper     evacuation, cleaning (heating) and inflating procedures (e.g., purified, dried N2 or He).



Fig. 3:    The operation of a diffusion pump

Fig. 4:     The construction of a diffusion pump


Table 1:    Materials used in a typical diffusion pump

Sr. No


Material Specification


Jet assembly

Al (Spin hardened aluminum)


Pump body

SS, 304


Top flange

SS, 304


Bottom plate

SS, 304


Backing flange

SS, 304


Cooling coils




SS, 304


Water nozzles

SS, 304






The annular area of intake of diffusion pump is given by:

                                  A =    { D2– (D – t)2 }    

Where D, is the diameter of intake port and    is the throat width. At 20°C, the maximum pumping speed Smax of diffusion pump is given by:

           Smax = 11.6 A       L/s

In general, a pump with a pumping speed of 1,000 L/s would require an inlet port of about        22 cm [2].


1.    Basic Performance Factors

5.1  Pumping speed

        The pumping speed of a diffusion pump is constant once the optimal fore-pressure and the working- fluid temperature necessary for its operation are reached. The pumping speed is principally limited by the diameter of entrance/ opening of the pump. The efficiency of the gas removal is determined by the rate of diffusion of the gas pumped and the momentum transfer between the molecules of the pumping fluid and the pumped gas. Thus, the pumping speed of diffusion pumps increases with decreasing molecular weight of the pumped gas. In other words we can say that hydrogen and helium are removed more quickly from a vacuum line than nitrogen, oxygen or argon. The pumping speed also increases with the molecular mass of the pumping fluid. The pressure prevailing in the vacuum lines affects the pumping speed as well.

        The rate of gas removal increases from zero at pressures above the fore pressure required for the functioning of the pump to a maximum value, remains constant over several orders of magnitude of decreasing pressure and then declines. The point of decline is broadly related to the attainable base pressure. For example, the maximum pumping speed is maintained to a lower pressure when SANTOVAC-5 is used and higher rather than Silicone-702 is used as a pumping fluid. The vacuum regions and pumping speed levels in a diffusion pump are shown in Fig.5. Compared to other fluid entrainment pumps the density of the vapor in the boiler and in the vapor jet is fairly low so that the gas molecules may almost completely diffuse into the vapor jet. Thus most of the molecules which enter the vapor jet are also pumped out. For this reason, the pumping speed of diffusion pumps is extremely high with respect to the intake area [13-15].







Fig. 5:   The vacuum regions in a diffusion pump

5.2 Compression ratio

The diffusion pump is similar in characters to other compression pumps because it produces a relatively high exhaust pressure compared to the inlet pressure. For most gases this compression ratio may be one million to one (or greater). For example; for an inlet pressure of 2.0×10-7mbar and a fore line pressure of                       2.0×10-1mbar, the compression ratio would be one million. As far as compression goes, in a mixture of gases, each species may be pumped with different effects. It is possible to have different maximum compression ratios and different flow rates for gases having different molecular weights. For example, the compression ratio for hydrogen will differ greatly from the compression ratio for argon simply because their molecular weights are very different. Also, when the pumped gas has a molecular weight different from air the maximum compression ratio will shift, but the tolerable fore line pressure (critical discharge pressure) remains the same.

5.3  Backing pump requirement

 In order that the basic process (diffusion) of gas removal can work efficiently, a low pressure must exist in the pump to start with. This is created by a mechanical pump. So, before the diffusion pump is connected with a system it is evacuated in the range of 10-1 mbar using a rotary pump. Similarly, the diffusion pumps cannot be exhausted to atmospheric pressure, hence it is always backed by a mechanical pump, mostly in the form of rotary vane pump. The initial pressure, required for a diffusion pump to start to work properly, varies with the design as well as with the type of gas that is being pumped, but must be in the range of 10 to 2 mbar.

5.4  Critical discharge pressure

The critical discharge pressure of a diffusion pump is the maximum permissible pressure at the fore line during normal pump operation. The expected pumping action of a diffusion pump ceases when the critical discharge pressure is exceeded. That is, the vapor of the discharge stage of the pump does not have sufficient energy and density to provide a barrier for the air in the fore line, thus, this air will flow through the pump in the wrong direction carrying with it the pumping fluid vapor. For most modern diffusion pumps, the maximum allowable fore line pressure is about 0.5 mbar. The diffusion pumps cannot function at all unless the fore line pressure is held below this limit by the backing pump. The most important rule of diffusion pump operation is: Do not exceed the critical discharge pressure! If this single most important rule is observed, then most difficulties associated with diffusion pump operation can be eliminated.

5.5 Ultimate pressure

Two distinct observations can be made regarding the ultimate pressure of a diffusion pump. Ultimate pressure may be considered to be a gas load or a pressure ratio limit. The pressure ratio limit is usually associated with light gases (hydrogen, helium, xenon). The pumping action of the vapor jets does not cease at any pressure. The ultimate pressure of the pump depends on the ratio of pumped versus back-diffused molecules, plus the ratio of the gas load to pumping speed. Also, the pump itself can contribute a gas load either through back streaming of pump fluid vapor and its cracked fractions or the out gassing from its parts. In practice, then, the ultimate pressure of a pump is a composite of several elements. The first limit of the ultimate pressure is usually due to the vapor pressure of the pumping fluid, although this limit may not be observed at pressures below 10-8 mbar.

5.6 Back streaming

 Back streaming can be defined as the passage of the pumping fluid through the inlet port of the pump and in the direction opposite to the direction of desired gas flow. However, back streaming must not be limited to the pump, but must include the trap, baffle, and plumbing as well because all affect the transfer of pumping fluid vapors from the pump body to the chamber. There is a multitude of conditions that can cause back streaming. The most common are; exceeding the critical discharge pressure in the fore line, exceeding maximum throughput capacity for long periods of time, and incorrect start-up or shutdown procedures. Back streaming of pumping fluids into your work environment is always considered catastrophic. I know of very few vacuum related processes in which oil contamination is not a disaster! My suggestion to system operators is to know their equipment thoroughly and learn proper operating techniques. Ninety-nine percent of costly back streaming problems are due to operator error. Finally, equip your system with the appropriate interlocks that will prohibit valve cycling above a specified pressure. This will protect your system whenever it is

5.7  Vacuum range

         The vacuum range in a diffusion pump is    10-3 mbar to 10-10 mbar, depending upon what type of baffle or trap is being used to minimize back streaming rate.

5.8  Tolerable fore pressure

         It is the maximum allowable pressure in the fore-line. It is closed to 0.5 mbar in a diffusion pump.

5.9  Maximum throughput

         It is the maximum capability of a pump to transfer gas in mass flow rate units.

5.10 Back streaming rate

         The rate at which the pumping fluid vapor leaves the inlet opening of the pump moving back in the direction of the vacuum system being pumped is known as back streaming rate of that diffusion pump.

5.11 Baffles and traps

         Baffles have one particular purpose: to reduce the back streaming of pump fluid into the vacuum chamber. Most baffles are “optically opaque” which implies that their internal geometry is such that light cannot pass directly through them. This insures that a molecule will collide at least once with a surface regardless of the incoming direction. Baffles do impede the flow of pumped gases, but well-designed units can retain about 60% of the pumping speed. Baffles are installed directly above the pump inlet and are often used in conjunction with a trap. Water-cooled baffles can reduce the rate of re evaporation of condensed fluid thereby reducing the density of vapor in the space between the baffle and the trap. The cryogenically cooled traps serve two purposes. They act as barriers against the flow of condensable vapors from pump to system; and they also serve as cryo-pumps for condensable vapors (primarily water vapor) emanating from the system. In typical unbaked systems, water vapor may constitute about 90% of the remaining gas after initial evacuation. The chilled traps increase the pumping speed for water vapor and therefore it lower the base pressure of the system.

  1. Diffusion Pumps’ Fluids

        The pumping fluid is very important in determining the characteristic and efficiency of a diffusion pump. The whole operation of the pump is dependent on it. The vacuum range, pumping speed and the running cost of diffusion pump changes with the change of its pumping fluid. The initially designed diffusion pumps utilized mercury as fluid, but due to its toxicity it has been replaced and rarely used in modern pumps.  There are several types of oils, based variously on silicones, hydrocarbons, esters, perfluorals, and polyphenyl ethers that can be utilized as pumping fluid in a diffusion pump. The most of modern diffusion pumps used silicone oils or polyphenyl ethers as the working fluids. The silicones oils were first used by Cecil Reginald Burch in 1928 [3]. The Criteria for selection of pump fluid includes low vapor pressure at room temperature, low toxicity, chemical inertness, molecular weight, heat of vaporization and cost. All of the oils would have a higher boiling point at full atmospheric pressure. Oils having lower molecular weights tend to boil at the lower end of this range; polyphenyl ethers, having higher molecular weight (446) boil between 230°C and 270°C, near the high end of the temperature range. The vacuum chamber may have a switch that automatically shuts the pump down when the temperature begins to rise. The various oils also have different thermal breakdown temperatures–the temperature at which the oil molecules break down and combine with any available oxygen. For pump operation, the boiling point of the oil is not particularly important, but the thermal breakdown temperature may have a priority. The oils with low boiling points also tend to have lower thermal breakdown temperatures [15, 16].

        The pumping fluid should have the following characteristics:

  • Low vapor pressure
  • Oxygen compatible
  • Non-flammable
  • Solvent resistant
  • Low relative weight loss
  • Chemically inert
  • Excellent compatibility with metals, plastics, elastomers
  • CFC-free (ozone friendly)
  • Corrosion resistant
  • High thermal stability
  • High dielectric properties
  • No flash or fire point
  • Reclaimable

Some of the important fluids used in diffusion pumps are:


SANTOVAC-5 is chemically polyphenyl ether. It is synthetic fluid which is capable of producing vacuum in the 10-10 mbar range. This fluid has extremely low vapor pressure therefore it has very low back streaming characteristics, than any other fluid resulting in less contamination and longer operation. SANTOVAC is ideal for use in many applications including laboratory, analytical and research operation, vacuum production, thin films, space simulation chambers, and optical coatings. Other major advantages are the following:

  • It is very pure fluid and as a result vacuum chambers and components remain cleaner, therefore, this results in less system maintenance and downtime.
  • It provides “extremely low back streaming” due to the inherent properties of this fluid.
  • The high vacuum properties and low back streaming properties will result in designing a system that does not require liquid nitrogen traps and baffles and ultimately allows for greater pumping speed and a much more efficient vacuum system.

6.2   DC – 702

          It is chemically, phenylmethyl dimethyl cycioxane [(CH3)3SiO] [(CH3)3SiO] [(CH3)3SiO].  It is designed for rapid pumping of large volumes of gas. It has the important advantage of thermal stability. This silicone based fluid is resistant to air at operating temperatures, so the pumps require no cooling between cycles.

6.3    DC – 704

          DC-704 is tetramethyl tetraphenyl trisiloxane with 4 pieces chain. It is a silicone diffusion pump fluid. This fluid’s low vapor pressure and thermal stability make it popular in processes such as vacuum coating, metallurgical work, and various other applications.

6.4   DC – 705

DC-705 is pentaphenyl trimethyl trisiloxane with 5 pieces chain. It is also a silicone diffusion pump fluid designed to produce an ultraclean vacuum. With the use of traps, DC 705 is capable of attaining a pressure of 10-11 mbar. Without traps, a pressure of 10-9 mbar can be achieved.

6.5   Invoil

The Invoil is specially distilled for use in diffusion pumps, where pressure of 10-7 mbar is required. This fluid is a standard fluid for mass spectrometers, leak detectors, distillation systems, and electron microscopes.

6.6   Invoil 20

Invoil 20 is also a high quality, general purpose hydrocarbon diffusion pump fluid that works well in any diffusion pump. The fluid is designed to meet the vapor pressure requirements of a diffusion pump while exhibiting excellent thermal stability. Invoil 20 can also be used in a mechanical pump.

6.7 Fomblin YH-VAC fluids

        Fomblin oils belong to perfluoropolyether (PFPE) family of lubricants. These are non- flammable, chemically inert and thermally stable. These fluids have excellent lubricity properties  and are available in viscosity grades suitable for use in all vacuum pumps. When used with proper filtration, these fluids provide exceptionally long service life. Fomblin YH-VAC fluids are suggested for applications requiring a high quality vacuum such as in scanning electron and transmission microscopes, mass spectrometers, particle accelerators, ion implantation, plasma and vapor deposition processes, etc. In addition, it is recommended for pumps handling reactive gases such as UF6, UF2, oxygen, ozone, tritium, etc. Direct contact with these gases will not result in any type of reaction or fluid degradation.

6.8  Apiezons

The apiezons fluids belongs to hydrocarbon family. These are low cost, low vapor pressure fluids suitable for general applications. The important types of these fluids are:

     A – natural hydrocarbons p (25oC) ~ 10-5

     B – distillated hydrocarbons p (25oC) ~ 10-7

     C – distillated hydrocarbons p (25oC) ~ 10-8

The properties of fluids used in diffusion pumps are summarized in Table-2, 3 and 4 [17].

  1. Operating Procedures

7.1 Precautions

The operation of high vacuum, diffusion pumping system requires certain care and attention to several items. General cleanliness is extremely important, especially in smaller systems. Remember, if a drop of oil were to be trapped somewhere in your vacuum system, it may take days or weeks to evaporate that drop from your system. Humidity and temperature can be important in view of the constant presence of water vapor in the atmosphere. When your system is opened to the environment, pump down time is significantly longer if the air is humid. The time of exposure is also significant. If possible, the backfilling should be done with nitrogen or argon. For short exposures, this appears to reduce the amount of water vapor adsorption in the vacuum system.

It is extremely important to develop good habits in valve sequencing operations, especially in systems with manual valves. It is useful to have a “map” or schematic of system on control panel that shows valve locations and functions. A single wrong operation can result in very costly maintenance to the system. Automatic valve sequence controllers have been used widely for many years, and they all have    built in   interlocks to prevent accidental opening of the wrong valves. During the evacuation of a vessel, the suitable time, to switch from the roughing pump to the diffusion pump is very important. In practice, the transfer from roughing to the diffusion pump is made between 50 and 150 mbar vacuum. Below this pressure region, the mechanical pump rapidly loses its pumping effectiveness and the possibility of oil back streaming increases.


Table 2: Properties of important types of diffusion pump fluids

Table 3:     Properties of important types of diffusion pump fluids

Table 4:    Properties of important types of diffusion pump

Take following precautionary measures before the operation of pump [19].

  • Check that all electrical connections are tight
  • No electrical wire is bare
  • Oil level and color in both diffusion pump and rotary pumping unit is normal.
  • In case of first installation of electrical motor, the direction of rotor is clockwise
  • Power supply is adequate
  • All open ports are properly blanked
  • All required accessories are assembled on the system
  • System is leak tight in the required range
  • The pump body is installed vertical and plumb
  • Check that the mating flange on the system is horizontal

7.2    How to operate the system?

  • Close all valves
  • Switch on roughing pump and Pirani gauge unit, open the fore line valve and note down the vacuum status of the system
  • On achieving the vacuum status of 10-2 mbar, switch on backing pump and note down the vacuum status
  • On achieving the required vacuum status in the system, please switch on heaters of diffusion pump
  • Also switch on chiller or cooling fan
  • Fill the liquid nitrogen in cold trap
  • Then switch on high vacuum gauge and gauge control unit
  • Close the roughing valve and open the high vacuum valve, thus inline the diffusion pump with system
  • Please ensure that continuous backing process in taking place
  • In case of LN2 trap, please ensure that trap is sufficient cold before opening the value.

How to shut off the system?

  • Isolate the chamber by closing isolation valve
  • Switch off heater
  • Switch off vacuum gauges
  • After one hour approximately, please switch off chiller or fan

After some time please switch off the backing pump and make the system normal

DP – diffusion pump, BP – primary (backing) pump, V1 – backing valve, V2 – bypass valve, V3 – vent (air inlet) valve, V4 – high vacuum valve, G1 – fore-vacuum gauge, G2 – high vacuum gauge

Fig.  6:    The sequence of diffusion pumping system











7.3   Maintenance of Diffusion Pumps

A vacuum diffusion pump chamber is not particularly difficult to disassemble, but break downs beyond routine maintenance, the work may be quite difficult. The worst conditions occur, when there is a massive influx of oxygen and the heat rises to a level that degrade or decompose the pump fluid. Generally, this occurs when the roughing pump fails or when a port breaks, or when the cooling system is not functioning properly. In these situations, combination of high temperature and pressure tends to char the oil (a process that can create a glutinous mess that is hard to clean up) but exactly what happens depends on the type of fluid in the chamber, and the temperature at which it breaks down. The breakdowns with non-silicone hydrocarbon-based fluids are hardest to clean up. The residue is much like tar and is tenacious. After scraping out as much of the gunk as can be safely removed, maintenance personnel may use emery cloth followed by extensive, careful bead blasting (similar to sand blasting, but less damaging to surfaces, and particularly to the rather fragile aluminum jet assembly). Final cleaning stages may use alcohol or some other solvents, soapy water and de-ionized water.

7.4 Applications of Diffusion Pumps

The diffusions pumps are common in industry and research institutes. The followings are the main areas of applications of diffusion pumps.

  • Analytical instruments
  • Coating, ornamental
  • Electron tube manufacturing
  • Metallurgy
  • Optics
  • Outer space simulation
  • Particle accelerator
  • Petrochemicals
  • Pharmaceuticals
  • R&D laboratories
  • Semiconductor manufacturing
  • Coating, functional


  1. Gaede, Die Diffusion der Gase durch Quecksilberdampf bei niederen Drucken und die Diffusion sluft pumpe, Annalen der Physik, 46 (3), 1915
  2. Gaede. Die Diffusion der Gase durch Quecksilberdampf bei niederen Drucken und die Diffusion sluft pumpe, Annalen der Physik, 46 (3), 1915
  3. Vacuum Technology, 2nd Ed. North Holland Publishing Co., New York, USA, 1978
  4. Dushman and J. M. Lafferty. Scientific foundation of vacuum technique, 2nd Ed., John Wiley, New York, 1962
  5. Avery and R. Witty. Diffusion Pumps: a Critical Discussion of Existing Theories
  6. Phys. Soc. 59 (6), 1947
  7. Power. High Vacuum Pumping Equipment, Chapman & Hall, London, 1966
  8. Hoffman, B. Singh and H. John, Hand Book of Vacuum Science and Technology, Academic Press, San Diego, USA, 1998
  9. H. Hablanian. Diffusion pump technology, Trans. 6th International Vacuum Congress, Kyoto, 1974
  10. Vacuum Sealing Techniques, Pergamon Press Ltd., Oxford, UK, 1966
  11. Beck, Handbook of Vacuum Physics, Pergamon press, Oxford, 1966
  12. L. Ho, Physics, Vol. 2, 1932
  13. Toth. The relation of the fenomenological and kinetic theories of diffusion pumps, Proc. 7th International vacuum congress, Vienna, 1977
  14. Dushman. Scientific Foundation of Vacuum Techniques, New York, USA, Wiley, 1962
  15. H. Hablanian, High-Vacuum Technology: A Practical Guide, 2nd Ed., 1997
  20. Burch. Oils, Greases and High Vacua., Nature, 122, 1928
  21. Manuel E. Joaquim, Inside a Vacuum Diffusion Pump, Santovac Fluids, Inc. and Bill Foley, Varian, Inc.
  22. Vacuum Technologies, USA , 20



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As you know, monthly “Engineering Horizons” is the first & Leading Technical Magazine of Pakistan covering Process, Mechanical, Metallurgical, Mining, Electrical & Electronics fields under a single cover. We also feel pleasure in saying that this is the only magazine of its own kind & style, which is widely circulated in all Engineering Sectors of Pakistan.