Design overpressure relief pathway

[martukas]

Whenever the overpressure relief valve engages, the excess gas should be vented out of the ventilator, so as to avoid a fire hazard in case of operation with concentrated oxygen (see #656). Currently (as of v0.3 design) the oxygen sensor and oxygen relief valve manifold is a single piece. A barbed fitting may be installed into the overpressure valve, but then tubing must run out of the ventilator housing.

The tube could run to either:

• display panel
• filter panel
• back panel

Depending on where this output tube is routed, the design of the manifold may have to change.

Very likely the task will consist of the following sub-tasks:

• redesign the manifold according to overall routing strategy
• Make the NPT port wider (but same pitch and taper ratio) so the valve can screw in further down.
• Create anchor points on the manifold so it may be secured to the acrylic plate with hardware
• Select pneumatic through-hole fitting for acrylic panel
• Update all subassemblies and top-level internals assembly with new parts and an adapting tubing part to show the routing
• Update documentation to explain rationale, assembly steps, etc..

[martukas]

Now that we have a back-panel, this the exhaust should probably run to an additional exhaust port on the back-panel. This means that the overpressure component should be below the main equipment tray.

With the work in #1337 , it is starting to make sense to decouple the overpressue relief valve from the oxygen sensor manifold. Extra space on top of the panel could be used for venturis with longer straight paths and a potentially bigger oxygen mixing chamber.

So this basically consists of 2 tasks:

• decoupling the existing manifold into separate 2 parts
• creating an exhaust port on the back panel