How to build a PAPRa Fan Box (96mm)

How-To guide for building the Tetra PAPRa fan box (96mm) (April 2024 build).

Quick Synopsis

The Tetra Powered Air Purified Respirator requires that the air be purified; this purification is accomplished by powering a fan to pull air through a filter and then pushing that purified air through a hose to a mask worn on the face. This section contains the instructions for building the box that holds the fan and filter.

The main goal of this iteration of the fan box is to reach N99 filtration levels by ensuring that the power connector is dustproof and using an IP68-rated BNC jack.

WARNING: we provide no warranty, implicit or explicit, that this device will work up to an N95 specification, when built outside of a facility rated to do so. The only way to truly test one of these devices using something like a Portacount under controlled conditions.

This particular version of the PAPRA has been tested to pass at an N99 level, and likely passes at an N100/P100 level, since the build uses P100 filters. We do not have the equipment necessary to validate that this device passes at a P100 level.

Parts Required

This photo shows all the parts laid out for building this component:

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The assembly diagram is here.

3D Printed Parts

These parts should be printed at 0.2 or 0.15 spacing. They should be oriented such that the large plates are closest to the build plate:

Table 1. Table Printed Parts
PartPart NumberQuantityMaterialSupports required?STL File Location

The Fan Box (holds the fan)

P-TET-000140

1

PETG

No (Can have some in the nut pocket)

Fan box

Filter Interface

P-TET-000158

1

PETG

No (Can have some in the nut pocket)

Filter Interface

Filter Frame

P-TET-000159

1

PETG

No

Filter Frame

Weather Guard

P-TET-000143

1

PETG

No

Weather Guard

Fan Outlet Spout

P-TET-000144

1

PETG

No

Fan Outlet Spout

Fan Outlet Spacer

P-TET-000145

1

PETG

No

Fan Outlet Spacer

Fan Outlet Interface

P-TET-000152

1

PETG

No

Fan Outlet Interface

Spout ring

P-TET-000191

1

PETG

No

Spout ring

MOLLE Strap

P-TET-000153

1

PETG

No

MOLLE Strap

MOLLE Catch

P-TET-000154

1

PETG

No

MOLLE Catch

MOLLE Spacer

P-TET-000193

1

PETG

No

MOLLE Spacer

Gaskets

Gaskets should be cut from 2mm craft foam. Ideally, they should be cut by something such as Cricut (https://www.cricut.com/), but can also be cut using scissors or an Xacto knife so long as the templates are followed closely. The Cricut uses the supplied SVG files, and other cutters can use the supplied DXFs.

Table 2. Table Gaskets

Part

Part Number

Quantity

Material

Pattern (SVG)

Base Gasket

P-TET-000146

1

Craft Foam

Base Gasket

Fan Gasket

P-TET-000147

1

Craft Foam

Fan Gasket

Filter Gasket

P-TET-000148

1

Craft Foam

Filter Gasket

Outlet Gasket

P-TET-000149

1

Craft Foam

Outlet Gasket

Fan Outlet Spout Interface

P-TET-000152

1

Craft Foam

Fan Outlet Spout Interface

Vendor Bill Of Materials

These are components that need to be purchased. Prices fluctuate, and so are not included here. Alternative versions can be sourced, and we welcome edits for tested alternatives.

Table 3. Table Vendor Bill Of Materials (BOM)

Count

Description

URL

Number in Package

1

Sanyo Denki 9BMB12F201

Sanyo Denki

1

1

20 American Wire Gauge (awg) BNC cable

BNC cable

1

1

Dryer Vent Installation Tape

DryerTape

1

1

BNC Cable Jack Connector

Jack Connector

1

13

M4 16mm screws

13

M4 square nuts

1

BNC 20 gauge wire stays

Wire stays

1

1

Stealth Filters

Stealth Filters

2

These tools are recommended. URLs are for tools purchased and used in the building of the prototypes:

Table 4. Table Tool List
DescriptionURL

4-3/4 In. Bent Long Nose Pliers

Long Nose Pliers

A hex screwdriver for the m4 screws

hex screwdriver

Flush cutter

Flush cutter

X-acto knife

X-acto knife

3D Printer (note the size of the print bed for the fan box)

3D Printer

#0 Phillips head screwdriver

head screwdriver

CPAP hose cleaner (for maintenance)

CPAP hose cleaner

Cable Crimper

Cable Crimper

9/16 Nut Driver for the BNC

9/16 Nut Driver

Build Steps

Preparing the parts

Cut out the Gaskets Carefully.

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Cut the tape into small piece’s

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BNC Connection

A video on how to build the BNC connector:

Strip the red wire on the fan:

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Connect the smaller brass component to the red wire:

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Crimp the brass component to the wire:

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Test that the crimp went well by tugging on the brass component:

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Make sure to put the wires through the ground cylinder before connecting the brass component to the connector:

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Push the brass component into the center of the connector.

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Since the wire is braided, this step can be tricky, and a small item like a paperclip can help push the component into the middle of the connector:

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Check that the brass component is visible and flush with the interior plastic column in the connector:

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Tugging on the wire should not have the component pull out:

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Strip the black wire:

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Crimp the ground cylinder to the back of the connector with the black wire:

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Another angle of the crimp:

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Place the waterproof seal around the edge of the BNC jack:

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Build Fan Box Assembly

Place the Fan Outlet Spacer (P-TET-000145) into the fan:

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Place the Fan Outlet Spacer (P-TET-000152) into the fan:

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Note the orientation:

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Begin taping the Fan Outlets into the fan:

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Cover all of the air gaps with dryer tape:

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Place the base gasket (P-TET-000146) carefullyinto the fan box (P-TET-000140):

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Place the Fan Outlet Gasket (P-TET-000) inside the Fan Outlet Spout raised edge (P-TET-000144):

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Place the fan outlet spout (with gasket) into the fan box:

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Place the BNC jack into the fan box:

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Make sure the BNC jack is seated in the hexagonal space:

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Place the washer around the BNC jack:

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Place and the finger tighten hex nut on top of the washer and BNC jack:

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Tighten the hex nut with a wrench:

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Place the fan (with outlet spout) into the box, holding the gasket in place:

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Push the wires in to the fan box.

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Place the Fan Gasket (P-TET-000147) on the Fan box.

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Connect Filter Interface to Fan Box Assembly

Place the filter interface on top of the fan box:

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Place 4x M4x16mm screws through the filter interface:

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Secure the filter interface onto the fan box with 4x M4x16 screws using a hex screwdriver:

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Option to use an impact drill:

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Load the Filters into the Filter Frame

Place the Filter Gasket (P-TET-000148) onto the Filter interface (P-TET-000158):

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Place the stealth filters into the filter gasket:

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Place an M4 square nut into the center space of the Filter Frame (P-TET-000159):

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Fastening an M4x16 screw from the opposite side to hold the M4x16mm square nut in-place inside the Filter Frame using a hex screwdriver:

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Place the Filter Frame (with M4 nut inside facing down) onto the Filter Interface. Make sure you get the orientation correct and avoiding direct contact with the filter:

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Place 4x M4 nuts into the corner spaces of the Filter Interface, screwing in M4x16 screws in the process to secure the Filter Frame onto the Filter Interfac with a hex screwdriver:

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Remove the center-piece M4 scew:

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Secure the weather guard ontop of the fanbax assembly with an M4 screw using a hex screwdriver:

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Attach fanbox MOLLE strapped backpack

Insert the MOLLE Strap (P-TET-000153) into the MOLLE Spacer (P-TET-000193):

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Secure the MOLLE strap (with MOLLE spacer) onto fanbax with M4x16 screws with 2x M4x16 screws using a hex screwdriver:

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Secure the MOLLE Catch (P-TET-000154) between the MOLLE strap and fanbox with 2x M4x16 screws using a hex screwdrivef

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Congratulations!

Congratulations! You’ve now built a Tetra PAPRa Fan Box!

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Questions

How frequently should I change the filter?

Changing the filter depends on how much you use the device. If you’re using the device where there are a lot of particulates in the air (such as a construction site or a woodshop), you may want to change every month or so. If you’re using the device where there are less particulates, every two to three months should be fine. HEPA filters just get dirtier and eventually the fan will have a hard time pulling air through the filter, and the filter should be swapped before that happens.

Can I use any random HEPA filter?

This particular box was built around the Klein Tools p100 filter. Off-brand filters may not be as effective, so be sure that the filter is NIOSH certified.

Is the fan box waterproof?

No, the fan box is not water proof. With the weather guard in place, water should not get into the filter directly, but increased humidity could decrease the effectiveness of the device.

Any other maintenance tasks?

It is important to periodically check that the nuts are tight on the fan box, to ensure that the box is properly sealed against the elements. Hoses should also be cleaned periodically as well.