Pure Air Circulator Unit Chapter 3: Description
Rev F, October 4, 2017 Page 3
Chapter 3 Description
3.1. Introduction
The Pure Air Circulator Unit (PACU) is a stand-alone, closed-loop filtration system. It consists of several filters that
remove moisture and particulates. The unit is designed to operate in a closed-loop fashion. The exhaust or clean
air enters a cavity that is sealed from the external environment and exits that cavity back into the PACU. The PACU
is ideally suited for the continuous filtering and circulation of extremely clean, dry air (or nitrogen) in an optical cavity.
If the PACU is to be used in an open-loop system, the moisture trap should be monitored often, since the filter is
removing moisture from the surrounding environment.
A pump and three filters produce a continuous supply of extremely clean, dry air. An adjustable speed, micro-
diaphragm, in-line pump pumps the intake air into a conglomerate of filters.
Filter 1 is filled with an indicating desiccant for the removal of moisture, impurities, and particulates from the
circulated air. Filter 2 is also an indicating type molecular sieve to absorb volatile organic compounds (VOC). Purified
air then enters the final Filter 3 to remove any particulate sized greater than 15 um. This filter traps fine particles in
a dense matrix of a sintered element. This sintered metal filter’s elements are manufactured from stainless steel
powders via a powder metallurgy process.
In typical closed-loop operation, clean air is filtered into a closed cavity and then pulled back into the circulator to
be processed again to remove any additional moisture or particulates. It may be used in open-loop operation, the
indicating desiccant should be monitored and replaced if saturation has occurred.
3.2. Setup Description
The Thorlabs PACU Pure Air Circulator Unit is a self-contained unit that may operate as a tabletop unit or may be
rack mounted in a standard 19-inch rack cabinet. Access to the intake and supply line must be available. If the unit
is to be used in on a tabletop, then the rack ears and handles may be removed.
We recommend that the supply line tubing be a good-quality, low outgassing type, such as
fluoropolymer. This kind of semi-flexible tube maintains high integrity with less cross- contamination. We
use 3/16" ID x 1/4" OD x 3/32" wall, 266 PSI Chemfluor 367 Tubing throughout the unit.
Because the unit is self-contained, it is only necessary to connect the 1/4” tubing to the device that needs
to be purged with clean air.
The user should consider where the pure air will enter the unit and where the exhaust air will be drawn out
of the unit. Best results are achieved if the intake and exhaust are in the same plane, but this is not
absolutely necessary.
If the unit is in open-loop mode, or the volume to be purged is exposed to external air (moisture), then
periodic checks on the indicating desiccant are necessary.
The system uses a switchable power supply capable of 110 – 230 VAC, 50 – 60 Hz (90 – 264 VAC,47 –
3.3. Features
Closed-Loop Air or Nitrogen Filtration System
Adjustable Air Flow by Pump Speed
Sight-Gauged Air Flow Meter
1/4"Quick-Connect Hose Connections
3.4. Replacement Parts
Filter 1 – Desiccant Filter (PACU-FTR1)
Filter 2 and 3 (sold together) – In-Line 15 µm filter and Molecular Sieve (Part Number PACU-FTR3)
Tubing - 3/16" ID x 1/4" OD x 3/32" wall, 266 PSI, Chemfluor® 367 Tubing
