Bag Sizing

13 April 2020

This page details various bag sizes and why the bag supports in any design should be adjustable. The key is to find points on each bag that provide support and lateral constraint, but do allow the bag to flex as it is compressed. The bag should be centered laterally and vertically between the grippers. The table below gives dimensions at the contact points and the center of the bag. We place the bag with the bottom towards the motor and head, with patient valving, overhanging. Remember, this valving must be extended as described in Plumbing.

For practical purposes, spacing the bag mounts 21 cm apart should fit most bags, but the mounts must have vertical adjustability.

bagdistancebottom øtop øcenter ø
Ambu Spur II
& Adult Silicon
Care Fusion2154.550134
Laerdal The Bag21na40139

Below are pictures of each bag type that we measured, shown in Version 2:
Note: In Version 3 we added hooks and an elastic to prevent unintended bag removal.

Ambu brand bag, note use of barb fitting to secure rear of bag

Using a phone level to position a Care Fusion bag
The Laerdal bag is large. Care must be taken to not pinch the bag when compressed and, as seen here, the bag lifts up and out in current configuration. This is not a good fit and longer arms are needed.
The Portex bag is cool because it comes in purple, but it is hard to secure properly.

28 Replies to “Bag Sizing”

  1. Jim Sullivan
    Jim Sullivan

    Also, any consideration to using thin quick release fasteners, such as velcro straps, on the plexiglass ends to secure the bag so it wouldn’t be accidentally moved or dislodged? It might also solve the Portex bag problem, and the bag could still be quickly removed for manual use in case of an error or malfunction.

  2. Diego Rodriguez
    Diego Rodriguez

    Good morning team, You had mentioned US Air Project printing the valve manifold for use, do you by chance have the file? Did they make you one? We have a team of engineers working through the production of these units and outside all the information readily available, this is one piece of puzzle we are hoping to not recreate. So far we have PCB design done, materials en route, and CNC/3D Printing resources lined out. Excited to start building.

  3. bhavesh bhatt
    bhavesh bhatt

    There is always a chance that “Ambu” bags and such will be in short supply also, various labs are using same bags with different ways to compress it, why not use a bellows based machine, where the bellows can be made locally by locally made materials (leather, vinyl, rubber etc).

  4. Art Jensen
    Art Jensen

    I have access to a large tier 1 supplier of injection molded parts and metal stamping. The owner and CEO is willing to have his mold shop and his plastics company make anything necessary. He is not looking for startup money or profits. He would like to see a device sold for under $1000.00 dollars and that is not a typo. They can produce thousands of parts daily. He has had the best 4 years of his companies history and wants to give back to America.

  5. Kathiresan Sundarappan
    Kathiresan Sundarappan

    In India, a group of doctors are against using this design of ventilator with bag. They can be convinced if it has been deployed somewhere in US or other countries.Can you please let us know what is the current status of testing, certification and deployment at Cambridge or other locations?

  6. Farrukh Nagi
    Farrukh Nagi

    Present system is bi-directional system and motor need to be reversed for inspiration and expiration cycle. Reversing motor for days is not good for motor controller and will have reliability issue. Why can’t one direction motor operation can be used with cranking wheel or Cam?

  7. Lok WM
    Lok WM

    From download 3D model, the bag holder distance is around 300mm. And the bag distance is 210mm. Do I have misunderstanding for the dimension? Does anyone have a detail dim spec for the bag? I am going to design the bag holder, wish someone can help me to get the about dim spec. Thanks!

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