An Engineer's Choice

  • Thursday, 24 March 2016

    [HOW TO] Select Required Vacuum Pump Capacity

    Today i wanna Demonstrate HOW TO SELECT VACUUM PUMP CAPACITY for a operation in pharma operations, especially pharma because the use of vacuum can make tremendous change in field of Pharma, one right selection of Vacuum pump can reduce huge efforts in specific operations like crystallisation, drying, saturation, Separations etc.
    So the its the main target of a process engineer or project engineer to provide with the right vacuum pump to manufacturing team for achieving high yields in small span of time, but before going to discuss about vacuum pump selection, i want all to know about the vacuum some more briefly,

    What is Vacuum? Vacuum is simply a pressure below atmosphere. To create vacuum in a system, a pump is required to remove mass (gas/vapor) from the system. The more mass is removed, lower is the pressure that exists inside the system. Various vacuum levels are defined depending upon the ultimate vacuum as:

                               Range                                Absolute pressure range ‰
                               Coarse Vacuum                          10 – 760 Torr ‰
                               Medium Vacuum                        0.001 – 10 Torr ‰
                               Fine Vacuum                              10^-3 – 10 ^-7 Torr ‰
                               Ultra High Vacuum                     < 10^-7

    Pumping speed: It is the volumetric rate of exhausting, generally expressed in Lts/min., m3 /hr or cfm. It is the rate at which the inlet of the pump actually removes the gas / vapor load. It should not be confused with Displacement of the pump. Displacement of a pump is the geometric volume swept by the pump per unit time at rated operating speed. For most of the pumps, pumping speed is close to displacement value at no load conditions (FAD-Free air delivery) and changes with inlet pressure, reaching to zero where the pressure attained is said be pumps ultimate pressure.

    The below data gives an approximate idea of how booster combination can yield lower pressures while maintaining high pumping speeds.
                                   Vacuum Pump              Pressure Range   Pressure Range with Booster

                                Single Stage Ejector             150 Torr                  15 – 30 Torr
                               Water Ejector                         100 Torr                  10 – 20 Torr
                               Water Ring Pump                  40 – 60 Torr             5 – 10 Torr
                               Liquid Ring Pump                 20 – 30 Torr             2 – 5 Torr
                              Piston Pumps                          20 – 30 Torr             2 – 5 Torr
                              Rotary Piston Pumps             0.1 Torr                     0.01 Torr
                             Rotary Vane Oil Pump          0.01 – 0.001 Torr       0.001 – 0.0001 Torr.
    Vacuum Booster being a very versatile vacuum machine is used in a wide range of processes, some of them being;
    Coarse vacuum applications
    • Vacuum Drying Application.                                • Tray dryer
    • Rotary vacuum dryers                                           • Flash Drying
    • Vacuum Distillation processes.                             • Solvent recovery.
    • Vacuum Filtration                                                  • Replacement of Steam Ejectors.
    • Enhancing the performance of Water Ring Pumps /Water ejectors
    • Vacuum Flash cooling / Evaporative Cooling        • Vacuum Crystallization
    Medium Vacuum applications
    • Efficient backup for Diffusion Pump Systems.     • Thin Film Deposition /Coating
    • Short path/ Molecular distillation.                         • Solvent Recovery.
    • Vacuum Heat Treatment and Degassing / Vacuum Furnaces
    • Freeze Drying                                                        • Vacuum Impregnation
    • De-humidification                                                 • De-gassing

    And Now i think you gained some brief knowledge regarding vacuum, and now i'll get into point directly of selecting a pump capacity,

    Also Read:

    For an installed system air leakage load can be estimated by Drop Test / Pressure rise testmethod. Based on the fact that air leaks into the system at a constant rate as long as the pressures in the system is below 400 Torr because of critical flow conditions, the above test is effectively used to determine the leak rate of assembled system.
    The system is evacuated to pressures between 10-100 Torr and isolated. The pressure is allowed to rise, but not exceeding about 300 Torr and the time lapsed is noted.

    * The Leak Rate “QL” is calculated as, 

    QL = PxVs/ t
    where QL leak tare in Torr Ltrs/sec 
    P pressure rise in Torr
    VS system volume in Litres 
    t is elapsed time in seconds 

    * For the known leak rate, the capacity of vacuum pumping system can be evaluated by the expression, 
    Savg = 3.6xQL P
    Where Savg = Average pump speed in m3/hr 
    QL = Leak rate Torr ltr/sec
    P = System Pressure in Torr 

    * As a thumb rule for pressures in the range of 10-100 Torr pipeline “D” may be selected as
    D = 2.4 (Q)^0.5

    where D= diameter of pipe in mm

    Q= Pumping speed in M3/hr .

    Thats it Cheers, comments are appreciated,

    Many of the readers found this somewhat difficult to calculate, and for them i've simulated these in an excel sheet, and download this excel sheet below.

    About The Author

    Hi! I am Ajay Kumar Kalva, Currently serving as the CEO of this site, a tech geek by passion, and a chemical process engineer by profession, i'm interested in writing articles regarding technology, hacking and pharma technology.
    Follow Me on Twitter AjaySpectator & Computer Innovations


    1. When do we select oil vaccum pump .. Steam circulation pump .water circulation pump ?

    2. Mostly that depends upon the case, if we need a vacuum of range 400torr-600torr that to while operating a system like steam under vacuum, we will go for water circulation pump and basically the vacuum attained from the water circulation pump depends upon the water temperature in the sump,

      and when ever we need some thing like coarse vacuum we will go for steam ejectors,

      and coming to oil vacuum pumps, there are two types, 1) oil ring pump- in this kind vacuum will be created through oil circulation and 2) oil lubricated rotary vane vacuum pump- in this kind just rotary vanes were used to create vacuum and oil is used to reduce wear-tear purpose, and when we need oil ring during drying and distillations(product layer concentrations, not solvent recoveries), and this oil ring pumps if the trap coolant is not efficient the vacuum attained will be low.......!!
      So based on the case we will go for vacuum pump.

      Still have any queries please feel free to ask

    3. Hello sir,

      I am working for a vacuum pump company practically I am dealing with lots of chemical application still I am having some doubts about pump selection for distillation and drying under vacuum.I want to stay connected with you to get clarified .Please help me by providing some mail mail id is


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