Primary Vacuum Pumps

Liquid Ring Pump

  • Accommodating to water & solvents
  • Very Forgiving


Rotary Vane, Oil-Sealed Mechanical Pump


Rotary Vane Pump

  •  Compact
  • Sensitive to solvents


Dry Vacuum Pumps

One Stage Roots Blower Pump Assembly


Roots Blower Pump

  • Dry Running
  • High operating speeds

High Vacuum Pumps: Oil Diffusion Pumps


Pump Construction


How Diffusion Pumps Work



Condensers to Enhance Vacuum

pV = nRT è

  • volume is reduces in transitioning from vapor phase to liquid phase, or vapor pressure decreases with temperature

Gas Flow Conductance

Viscous and Molecular Flow


Viscous Flow: 

Distance between molecules is small; collisions between molecules dominate; flow through momentum transfer; generally P greater than 0.1 mbar

Transition Flow: 

Region between viscous and molecular flow

Molecular Flow: 

Distance between molecules is large; collisions between molecules and wall dominate; flow through random motion; generally P smaller than 10 mbar


Vacuum Pressure Ranges




More on Vacuum

Vacuum System Configuration

Vacuum pumps

  • Liquid ring pump
  • Rotary vane pump
  • Roots vacuum pump
  • ScrewLine pump
  • Oil diffusion pump
  • Pump sets

Pressure measurement

  • Diaphragm vacuum gauge
  • Pirani vacuum gauge

Vacuum Pumping Methods

high_vacuum_short_path_distillation_thin_wiped_film_evaporator_thc_cbd_hemp_concentrate_isolate_crystalize_clear_terpenePressure of 1 Standard Atmosphere: 760 TORR, 1013 mbar or, at Sea Level, 0° C and 45° Latitude

Pressure Equivalents

Atmospheric Pressure (Standard) =


Vapor Pressure of Water at Various Temperatures

boiling_point_short_path_distillation_fractional_distillate_cbd_thc_separation_terpenes_clear_golden_oil_cannabis_hemp_concentrate _remove_smell_taste.png

Pressure Ranges








General Equipment Considerations



Major Components

  • 1 Feed
  • 2 Product distribution plate
  • 3 Heating fluid
  • 4 Vacuum nozzle
  • 5 Distillate
  • 6 Cooling
  • 7 Residue
  • 8 Heating jacket
  • 9 Roller wiper system
  • 10 Internal condenser


Horizontal Section Through A Short Path Distiller


Tasks of the Wiper System

  • Uniform distribution of the product onto the evaporator surface
  • Permanent mixing of the product film
  • Improvement of heat transfer from the heated wall into the product film
  • Exclusion of “Hot Spots“
  • Reduction of residence time

Characteristics of the UIC’s Roller Wiper System on all KDL and KDT Models

  • Open wiper basket design
    minimizes pressure drop between evaporation and condensation
  • Good mixing of the product film
    improves the evaporation of volatiles
  • Overlapping of wiper rollers
    avoids unwiped spots and formation of “Hot Spots“
  • Self-cleaning wiper elements
    minimizes maintenance
  • Short residence time
    reduces temperature history of product

Wiped Film Distillation

  • wiped_film_distillation_thc_cbd_short_path_fractional_separation_concentrate_clear_golden_water_terpene
  • Evaporation occurs on the wall of a cylindrical evaporator as the feed product falls down the cylinder wall and is heated above its boiling point by heat applied to the exterior of the cylinder.
  • Excludes the disadvantages of batch-distillation:
    • Lower pressure in the evaporator is possible
    • Reduces the residence time at high temperature, even in large units.

Result: Thermal decomposition is being avoided

Types of Thin Film Evaporators

  • Single Tube Falling Film Evaporator w/external condenser
  • Multiple Tube Falling Film Evaporator w/external condenser
  • Falling Film Degasser (packing) w/external condenser
  • Wiped Film Evaporator w/external condenser
  • Short Path Evaporator w/internal condenser

Thin Film (Wiped Film) Evaporators


  • Residence time:
    less than 1 minute
  • Pressure range:
    down to 1 mbar
  • Not an equilibrium device
  • ~ 1 theoretical plate
  • Condenser is external to Evaporator
  • 30oC rule —

   pressure f( temperature)


Falling Film Evaporators


Residence time: several minutes

often with recycling

Pressure range: down to several mbar Not an equilibrium device

~ 1 theoretical stage

Short Path Evaporators
(a subset of Wiped Film Evaporator)


  • Residence time:
    less than 1 minute
  • Pressure range:
    down to 0.001 mbar
  • Not an equilibrium device
  • ~1 theoretical plate
  • Condenser is inside the Evaporator
  • 30oC rule

Wiped Film   vs. Short Path

  • Thin Film Evaporator
    – External condensation
    –  Lowest operation   pressure: ~ 1 mbar
    –  Main application:
    Separation of high   contents of volatiles
  • Short Path Distillator
    – Internal condensation
    –  Lowest operation   pressure: 0.001 mbar
    –  Main application:
    Distillation of heat   sensitive products


Vacuum Pressure Conversion Table


Distillation Method Vacuum Potential (mm Hg) AEBP Potential Comment
Batch w/Condenser 50 465°C


Long holding period (at OBP)

Single tray

Fractional Column 20 500°C



Multiple trays possible

Good separation

Packed Column 20 500°C



Single tray device

Good separation

Wiped Film Evaporator 1 585°C


Medium AEBP

External Condenser

Single tray device

Short Path Evaporator 0.001 740°C


Very High AEBP

Internal Condenser

Single tray device


Practical Benefits of Vacuum Distillation

High Vacuum Short Path Distillation offers a number of benefits for processing superior cannabis concentrates.

  • Boiling Points of materials are significantly reduced under vacuum (30oC rule)
  • The partial pressure curves of different materials may indicate the application of vacuum will facilitate the separation process and purity of the distillate.
  • Vacuum usually accelerates the evaporation rate to accomplish separation of materials more quickly.