Passive vs Active: Which will work best for me
Best Value Vacs offers a wide array of options for closed loop hydrocarbon extraction. You have chosen
the unit that best fits your needs, but are unsure if you need a passive or active system. What is the
difference and how can you determine which will work best for you? Let’s first discuss how each style
Passive Recovery works by manipulation of temperature and pressure. In a closed system, gas will
always seek the lowest pressure it can. Using this simple bit of knowledge, hydrocarbon gas can be
moved from one part of the system to another by making sure the pressure on the receiving end is
lower. This is accomplished by manipulating temperature. The pressure of a hydrocarbon is directly
correlated to the temperature. If you refer to the graph below, you can see temperature and the
corresponding pressure for butane and iso-butane.
By heating the butane liquid in the collection base and cooling the receiving LP tank, butane vapor will
naturally move to the cooler area. If the temperature is below the boiling point of the solvent, vapors
will re-condense into a liquid. This method is a simple solution to recovering solvent and is often the
way beginning users learn how to operate a closed loop system. Passive systems tend to leave more
solvent behind, so solvent loss per run is usually higher.
Active recovery will follow the same principals as passive with the addition of a recovery pump. This
pump will aid the movement of solvent vapors by utilizing a push/pull action. By utilizing a pump,
solvent recovery is sped up. This method also helps reduce continuing cost by minimizing the need for
expensive chilling options, such as dry ice. The solvent is condensed into a liquid by using a coil located on
the output port of the pump. This method reduces the amount of dry ice needed to have a fast,
efficient recovery. The combination of efficient condensing of vapors and the force created by the
pump, solvent recovery tends to be faster when using a pump. This method does not require the LP
tank to be chilled, so active systems cost-effectiveness becomes greater as the capacity of the closed
loop increases. Being that a recovery pump can pull into the vacuum, less solvent can be left behind in the
extract. These systems tend to have less solvent loss per run. The major downfall of active systems is
that the pumps do need to be maintained and rebuilt periodically, so more attention is required with
Which option should I choose?
Passive systems are a great for the beginner, being that there is no need for electrical equipment to
move the solvent. These systems can be efficient with recovery speeds, however, a large amount of dry
ice is needed to do so. Regular ice can be used instead, but recovery times will be much larger. This
option is great for units with 1lb capacity or lower. They are also a good option if large production is not
a concern. If you have plenty of time to process and/or have easy access to bulk dry ice, passive is a
great option for you.
Active systems will reduce the need for large amounts of dry ice, but have a larger start-up cost. These
systems give faster recovery times per lb. of solvent used. These become especially attractive to those
who need to have large amounts of production or using large systems. These systems can also pull the
collection base into a vacuum when completed, so more advanced options for extract removal (i.e. cold
muffin technique) can be accomplished. If speed and production amount is a requirement or dry ice is
hard to come by, an active system should be your chosen option.