Pandemic Ventilator Project, Hacker News

So I looked for these tiny blowers. The reason they are small is not just so that they can be compact. They need to be high RPM with low mass of motor and impeller so that they can change the speeds very quickly so as to provide the desired pressure profile.

Such a pump is available, say from Digikey, but only a few dozen are in stock and then multiple weeks to order more. That won’t work for us. You could also get them from China. There are obvious supply chain problems there. One of my original requirements for the Pandemic Ventilator Project was that it be able to be built from parts that we already have around because I assumed supply chains would be disrupted by the pandemic as well. Well, that turned out to be true.

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The blower in this design is a big one that runs on AC and not a nice little low voltage brushless. (Sorry, no intrinsic battery backup here.) The blower runs full on all the time. (Will be noisy too.)

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In order to rapidly change the pressure there is a valve arrangement that opens the pressure control valve and closes the waste gate with the linear actuator shutting down the outlet flow to rapidly bring up the pressure to start the cycle. The motor operates a turning arm that is connected to the valves to rotate them so as increase or decrease the opening in the pipes. The motor could be a stepper or a fast turning motor with gear reduction and some method of angle feedback. (I am sure the RC model car guys can figure this out – it’s fundamentally like the steering part.)

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Pressure is then controlled by feedback from the feed pressure sensor adjusting the servo motor and additional fine tuning from the linear actuator controlled slot valve.

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The flow meter monitors the inspiratory volume. and when the conditions are met to exhale, the pump pressure is cut off by the servo motor and the linear actuator opens he slot valve to control the flow to the outlet. The linear actuator then adjusts the slot valve position to maintain a prescribed PEEP pressure utilizing feedback from the patient pressure sensor.

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with the right software, you could control rates, tidal volumes, minute volumes, pressure profiles, PEEP to whatever you want, and also offer patient controlled breath initiation.

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I added a filter to reduce cross contamination. and protect workers. I don’t know, that May be optional if everyone is wearing PPE in any case.

· What you actually now see is version 2. I reaarranged the layout to minimize dead space, I added the input tube for humidified oxygen increased air, and added a recirculation loop to minimize the waste of oxygen.

Anyway, this is my first shot at a design for this style. Actually, looking at it, it seems too simple a design to me. I must have left something out. I am sure readers will find flaws and maybe offer some design improvements. Any maker group, anywhere please feel free to use whatever you want from this.

Next Steps:

the design should be reviewed by experts in ventilator use as well as engineers with experience in device control to be sure it is adequate and relatively optimized.
Need to come up with a list of potential parts and interface criteria for sensors
• Specify control system processor, drivers etc.
  • Specification list (state table) for all modes of the device to aid in programming
    • Basic machine control program is written,
      Interface program for operator control, alarms and setup

  Modify interface look and feel to clone an existing popular ventilator design

Functional, safety and usability testing

• Operators manual.

All of these steps are of course iterative and involve testing and user feedback at each level

Parts List