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The SYSTEM OPERATION Of gas mask filters

2020/08/14

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The invention described herein may be made, used or licensed by or for the Government for governmental purposes without the payment to us of any royalties thereon.
 
FIG. 1
Compressed air enters the system at 60 psi with a minimum flow rate of 7 standard cubic feet per minute (SCFM) (1, FIG. 1). After passing through a regulator, desiccator, and prefilter (2,3,4, FIG. 1), the air enters the air distribution manifold (5, FIG. 1). The air distribution manifold distributes air to the filter chuck cylinder (6, FIG. 1), aerosol atomizer (7, FIG. 1), dilution air (8, FIG. 1), photometer (9, FIG. 1), drying/mixing chamber (10, FIG. 1), or exhaust port (11, FIG. 1). A vacuum pump draws (13, FIG. 1) air from the photometer outlet (12, FIG. 1) and air distribution manifold to be exhausted.
 
Air is supplied to operate the chuck at pressures up to 60 psi., generally 40 psi is sufficient to hold most filter cartridges. Air pressure to the chuck is controlled by an in-line regulator (14, FIG. 1). Air supplied to the aerosol generator is regulated from 0-30 psi (15, FIG. 1). The photometer purge air regulator (16, FIG. 1) is set to 10 psi. Dilution air supplied to the mixing/drying chamber is controlled by (17, FIG. 1) a in-line flowmeter. Air supplied to valve assemblies for mixing chamber and photometer switching valve assemblies is supplied at 60 psi, this is regulated by the air intake regulator (2, FIG. 1).
 
FIG. 2
Air flows from the air distribution manifold to the aerosol generator (1, FIG. 2), atomizer air is regulated to 20 psi for low concentration mode, or 30 psi for high concentration mode. In the low concentration mode, the 20 psi of air is supplied to a single nebulizer for aerosol generation. In the high concentration mode, 30 psi of air is supplied to 4 nebulizers to generate a more concentrated aerosol. The aerosol flows from the aerosol generator to the aerosol drying/mixing chamber (2, FIG. 2).
 
Dilution air comes from the air distribution manifold through a in-line heater (3, FIG. 2) used to heat the dilution air when a salt aerosol is being generated. When producing candidate material aerosols the heater is not used. The dilution air mixes with the aerosol from the aerosol generator to ensure a uniform concentration. The diluted aerosol leaves the mixing chamber and travels through a in-line flow controller (4, FIG. 2) to the chuck. Between tests, excess aerosol is exhausted from the mixing chamber to the exhaust manifold where it leaves the instrument (5, FIG. 2).
 
When the chuck is closed, aerosol is free to flow through the chuck (6, FIG. 2) and the filter material to be tested. A portion of the aerosol from the upstream side of the chuck flows to the scattering chamber (7, FIG. 2). A pressure gauge (8, FIG. 2) measures pressure differential between the upper and lower portion of the chuck to indicate pressure drop across the filter during tests. Aerosol leaving the downstream portion of the chuck is divided, a portion of the air goes to the scattering chamber, the rest is exhausted (9, FIG. 2).
 
Three streams of air enter the scattering chamber through the photometer switching valve assembly. Clean, filtered air from the air distribution manifold enter the manifold and scattering chamber (10, FIG. 2) between filter tests to clear aerosol from the chamber allowing the photometer to establish a baseline reading. Aerosol from the upstream side of the test chuck enter the photometer switching assembly (11, FIG. 2) and the scattering chamber during the test to establish a 100 percent aerosol concentration reading. After the 100 percent level is established, purge air clears the aerosol from the chamber. Aerosol from the downstream side of the test chuck is then introduced into the scattering chamber (12, FIG. 2). A percent of 100 reading is taken of the air which passes through the filter material being tested. Purge air and test aerosol is exhausted after leaving the scattering chamber (13, FIG. 2).
 
The microprocessor fully automates the test procedures. The test mode, flow rates, and length of test can be set up using the key pads on the instrument's control panel. Once set up, the operator only inserts the filter media and closes the chuck; from there the test is controlled by the microprocessor. An LED display gives a real time indication of the flow rates, pressure drop across the media, and percent penetration. At the end of the test, the chuck automatically opens; a report of the test results may be printed by the 8110's built-in printer.
 
For the purposes of qualifying the aerosol produced by the 8110, a TSI Differential Mobility Particle Size Analyzer (DMPS) was used to characterize the aerosol output. A sample of the aerosol was taken at the exhaust port of the 8110. The aerosol was diluted to measurable concentrations using a TSI model 3302 capillary diluter. The DMPS samples the aerosol and reports the aerosol surface mean diameter and spread factor.

 

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