40MM NATO (RD40x1/7) to Sundstrom SR Series Filter (SR100/200/900) Adapter

This prototype design for a 40MM NATO (RD40x1/7”) gas mask thread to Sundström SR series respirator (SR100/200/900) filter adapter. This adapter makes any RD40x1/7 threaded full face CBRN masks compatible with Sundström SR series line of chemical, combination, and particle filter cartridges to help mitigate PPE shortages by expanding greater cross compatibility of respirators and filters to other manufacturer models.

Part Description:

40MM_NATO_TO_SUNDSTROM_FILTER_ADAPTER_BASE_GEN1.stl
40MM_NATO_TO_SUNDSTROM_FILTER_ADAPTER_END_CAP_GEN1.stl
40MM_NATO_TO_SUNDSTROM_FILTER_ADAPTER_MAIN_GEN1.stl
40MM_NATO_TO_SUNDSTROM_TPU_GASKET_GEN1.stl
Initial model release of three part assembly, for ease of 3D printing, with included TPU gasket if user cannot source O-ring or gasket material from local hardware store.

Disclaimers/Risks:

1.) Use Proper Gaskets
It would appear that the non RD40x1/7 threaded SR series of filters feature a gasket on the filter side and also relying on the silicone sleeve on the respirator side attachment. However, since I do not have SR series filters or respirator, I could not ascertain the o-ring dimensions to design an adapter to seal against OEM gasket on filter side, and because of my concerns with using TPU to replicate precisely the geometry on the respirator side, I opted to use an alternative method to seal against SR filter. A threaded end cap applies compressive force on the angled outer face of the filter cartridge, which seals on the OD of the base of the filter cartridge against adapter TPU gasket. Ensure positive seal by tightening provided threaded end cap . See cutaway diagram to see interface of adapter. Recommended user place witness clocking marks to ensure that the end cap doesn’t back off during prolong use or routinely press check to ensure seal.

Recommended user apply thread locker/Teflon tape at base of RD40X1/7 adapter to the large circular main body after assembly of the base and main parts.

2.) Perform Proper Negative Pressure Test
Follow SSPs established by your institution or workplace for further guidance. But in general, don your respirator, adjust straps till taught against face, ensuring no obstructions around the periphery of the seal against face either due from hair, facial hair, or otherwise. Exhale deeply. Cover all inhalation ports. (Typically, most full face or half face respirators have two filters, so cover those intake ports with your hands. If your running only one filter, ensure the opposite port has filter cap in place.) Now inhale deeply. The mask should suck tightly against your face without any air leakages. Re-test if adjustments are required at gasket/o-ring interfaces at the adapter.

3.) Use At Own Risk – Temporarily Solution Only Until Supply Chain Normalizes
3D printing materials are not resistant to many solvents, are water soluble, and degrade when exposed to chemicals, heat, and UV/sunlight. 3D printing this adapter is only a temporarily ad-hoc solution against biological contagions. In addition to using a properly calibrated 3D printer, due to tolerances of adapters, if possible perform hot nozzle pass on all exterior surfaces, to reduce surface porosity. Highly recommended users apply a thin layer of polyurethane clear coat on all exterior surfaces, spray or dip based methods, to help resiliency and durability for repeated sterilization and to reduce fomite transmission in printed infill layers. Once supply chains return to normal, users should purchase OEM OSHA/NIOSH/EN standard approved respirators, adapters and accessories for their institution and workplaces.

Dev. Notes:

5/04/2020 - Initial model release. In work, pending support 3D printing community for any fitment and model revisions.