Introduction: S-Vent Simple Ventilator

New website now online here: www.s-vent.life

The S-Vent design is constantly being updated as I get feedback and make improvements, please check back regularly for the latest specification.

Updates:

  • Current max volume is 500ml with a slight modification and re-design to get to 600ml+, I will update with that soon.
  • 60 hour run test completed.
  • Have been asked about a Waters Circuit and/or Mapleson C, trying to get hold of one to see if it can be fitted.
  • New PEEP valve in the post and will be fitted as soon as it arrives.
  • Will add wheels and a mount for the battery to make it more portable soon.
  • Trying to source an HME filter to fit inline with the mask along with filtration.
  • Close to finalising the plans for testing on a lung simulator.
  • Cam design update to improve MVB inflation.

There has been a lot of attention on making high-tech ventilators for well resourced countries but we also need to think about places where there's no access to high-tech equipment and resources are limited.

The S-Vent is a simple ventilator I have designed to try and help with the current Covid-19 pandemic.

It is designed to use basic components and materials so that it can be produced anywhere without the need for 3D printing or machining.

It can provide the following features:

  • Variable tidal volume,
  • Variable cycle time (breaths per minute),
  • 1:2 Inspiration to Expiration ratio (Modifiable),
  • Presure relief valve (included in face mask that cam with bag),
  • Pressure gauge for Inspiration/Expiration pressue monitoring.
  • *PEEP valve and filter coming soon

It can run off a 12v car battery or 12v power supply for on and off-grid use. If you run a 12v power supply and car battery together the car battery works as a back up supply in case of main power failure.

I'll add more diagrams and instructions as soon as I can. Please feel free to make and share as much as you like. I think I've given it the right license so that anyone can take it, make it or modify it but if not let me know and I'll change it. From my perspective this is totally free for anyone to do anything with in the hope that it might help.

Any comments on how to make this design better or give more features would be great thank you.

Please note:

The S-Vent has been designed to be simple to manufacture while providing as many functions as possible to help provide ventilation to a patient. It has been designed Dr Tom Burton who has over 10 years of Medical Device design, manufacture and compliance and is a Senior Systems Engineer at McLaren Applied. However, the S-Vent has not been approved for clinical use. I have been working with respiratory consultants and tried to make the design as safe and easy to use as possible but the target use of the device is where no other option is available. In the coming few days I hope to trial the device with a lung simulator and it has already completed a 60 hour run-time test.

Supplies

For S-Vent (See picture of all parts):

    1. Manual Ventilation Bag (MVB)

    2. Air tube

    3. Pressure Relief Valve

    4. Mask (This will also be fitted with PEEP valve and filter in next version)

    5. 12v power supply or 12v car battery

    6. Windscreen wiper motor and fixing bolts

    7. PWM motor speed controller, a current controller is OK but not as good

    8. Bearing 8mm ID 35mm OD 10mm W

    9. Bolt and locknut M8 * 65mm

    10. Cam

    11. Motor coupler - I've used an aluminium metal shaft clamp but this could be made from plate steel or aluminium

    12. Cam spacer

    13. Motor spindle nut

    14. Main support beam

    15. Arm

    16. Bag clamp with large hole

    17. Bag clamp with small hole

    18. Bag support

    19. Slide guides

    20. Bag holder clamp

    21. Pivot support

    22. Pivot platform

    23. Metal corner brackets (or hinges or wood)

    24. Return bracket top

    25. Return bracket support

    26. Feet

    27. Motor mount

    28. Arm support and space material

    29. Resevoir bag for O2

    30. Wood screws 4X50, 4x35 and 4x20

    For the Pressure Gauge:

    1. Long wooden plank

    2. Wooden base and support

    3. Small plastic bottle with lid

    4. Glue

    5. 4mm OD 2.5mm ID clear pipe (or near enough) approximately 3 meters

    6. Tape

    7. Wood screws

      Gaffertape and cable ties also useful.

      Step 1: Cut-out All the Parts

      Using a circular saw, jigsaw or hand saw carefully cut out all the parts using the plans in the pdf attached.

      Make sure to file off any sharp edges.

      Step 2: Assemble the Bag Holder

      Using wood screws attache each bag clamp to either end of the bag support.

      Turn the holder over and place a piece of wood the same profile as the main support beam in the middle of the bag support.

      Place the two guides either side of the main support beam stand in and use a small piece of thin card to make sure they don't become too tight once fixed in place.

      Screw the guides into place and remove the card.

      Fix the bottom plate in place with more wood screws, be careful not to over-tighten as this will make it difficult to move.

      Finally turn the section over and check that the bag fits snugly in the holder.

      Step 3: Assemble the Arm Pivot

      Place the arm in the middle of the top support and screw in the corner brackets either side of it making sure they're snug but not to tight. If it's not quite aligned straight this is ok, you can correct it later by gently moving the arm left or right to slightly bend the brackets and straighten it.

      Screw the top onto the support, turn the section over and attach the main support beam.

      Step 4: Cut the Bearing Hole

      On one end of the arm make a mark 15mm from the end and along the centre line. Repeat this for each side of of the arm and use a small drill bit to create a pilot hole on each side.

      At the other end make a mark in the centre of the arm 750mm from the two holes you just drilled (see pictures).

      Draw a box 40mm by 14mm around this line.

      Use a 10mm wood drill at each end to start cutting the hole.

      At this point I found it best to drill the hole for the bearing bolt as if you do it after the wood could split. To do this use a 10mm wood drill and make a hole through the centre of where the bearing will sit.

      Remove the rest of the bearing hole with a jigsaw or chisel and tidy up any rough edges with a file.

      Place the bearing in the hold with a washer either side of it.

      Push an M10 bolt through the hole and secure with a nut, nyloc if possible.

      Step 5: Attach the Arm

      Attach the arm to the base by screwing through the top hole of the corner bracket into the small pilot hole drilled in the previous step.

      Once you have done this for each side you can check the alignment of the arm with the support base, if they are not quite strait a gentle pull left or right on the arm would bend the brackets into place.

      Slide the bag support onto the main support beam and check it moves freely, adjust the hole with a file if there is any sticking at all.

      Step 6: Motor Mount and Spacers

      For the motor mount make a 25mm hole (or larger depending on the type of wiper motor you have) in the motor support. Use the plans to make sure the hole is in the correct place for when you attach the mount to the device.

      Place the wiper spindle through the hole and use a pen to mark where the supports go.

      Drill out the holes for the supports so that the bolts can reach through and engage with the threads.

      Cut out the cam spacer, make sure the hole in the centre is big enough to be able to get the socket for the motor spindle nut through.

      Make sure the motor coupler fits snugly over the grooved section of the motor spindle and make sure there is enough clearance to tighten the spindle nut without causing the coupler to interfere with the motor mount.

      I had to modify the hole in the motor coupler I was using to fit with a hole drill bit, the profile for the hole in the motor coupler will depend on the type or wiper motor you are using. This could be made with a piece of plate steel or aluminium, make sure to add some holes for screws to secure it to the cam spacer.

      It's really important that the motor spacer can go far enough down the shaft to allow the securing nut to be fastened to it but not too far that it hits the motor mount and increases friction when rotating.

      Step 7: Fix Motor and Spacers

      Fix the motor to the motor mount with bolts.

      Mark the cam space so you can locate the coupler in the centre of the hole and fix the coupler to the cam spacer with wood screws or bolts.

      It doesn't matter if it's not exactly in the centre as you will see later. just make sure you can get a socket through to tighten the spindle nut.

      Place the motor coupler over the spindle and secure with the spindle nut.

      Make sure the motor can still rotate freely.

      Step 8: Cam Profile

      To cut out the cam profile mark the centre point of the cam and then draw lines every 30 degrees around it.

      Using the cam profile spreadsheet, or attached pdf, mark the distance from the centre of each section of the cam in turn.

      i.e. if at 30 degrees the height should be 50mm then make a mark along the 30 degree line 50mm from the centre.

      See the first picture for how to do this.

      Repeat this for each of the marked lines and then draw around it with a smooth curve.

      Cut out the profile and smooth off the edges with a file.

      Fix the cam to the cam spacer by using wood screws, here you need to make sure the centre of the cam lines up with the centre of the motor spindle.

      Step 9: Motor Mounting

      Mount the motor so that the centre of the cam is at the correct height from the support bar and at the correct distance from the arm pivot point.

      Secure in place with wood screws.

      Step 10: Cam and Arm Guides

      Join the two cam guide sections with wood screws and fix 150mm from the end of the arm.

      If necessary add some extra thickness to the arm guide and screw in place making sure it doesn't interfere with the bearing bolt.

      Step 11: Wiring and Power Supply

      Remove and unnecessary wires from the wiper motor and attach the positive and negative cables to the output of the speed controller.

      If the cam rotates in the wrong direction just switch the wires over.

      Being careful to observe the correct polarity, connect the input to the speed controller to the 12v power supply or car battery.

      Step 12: Final Fittings

      Attach the reservoir bag and O2 pipe if included to the bag.

      Check that the motor controller varies the speed of the cam from 12rpm to 30rpm.

      Check that the arm compresses the bag sufficiently and that the bag support is free to slide up and down the support beam.

      If needed add padding to the arm to reduce the chance of damage occurring to the bag.

      Finally fit the pipe and mask and check that everything is functioning correctly.

      To help with the correct tidal volume administered you can draw lines at set interval along the support beam which line up with the bag support structure. To calibrate these lines perform the following procedure:

      • Remove the mask from the end of the air tube.

      • Place a plastic bag around the now open tube and wrap a rubber band or tape around it to stop air leaking out. Ensure there is enough of the plastic bag still able to be inflated to about 600ml.

      • Cut the top of a 2ltr bottle of get a measuring jug with a capacity larger than 1ltr. Place the container into a large Tupperware or something to catch over-spill.

      • Place the deflated bag into the container and use a piece of wood to hold the pipe at the bottom of the container, otherwise it floats to the surface.

      • Fill the container (bottle or jug) to the brim, I used the bucket first and then the measuring jug - fill the container until the water is just about to spill over the edge.

      • Move the bag support to a position on the support beam and allow the cam to move from zero to maximum compression. This will inflate the plastic bag and the displaced water will over flow the top of the container, this is ok

      • Pour the over-spill water from the Tupperware into the measuring jug and record the amount in ml - this is the amount of air delivered.

      • Mark the position of the bag support on the support beam and write the volume of air displaced at this position.

      • Repeat this for a number of positions between maximum and minimum movement of the bag support along the support beam, be sure to do maximum and minimum and at least 3 steps in between.

      Pictures on how to do this coming soon - now in a later step.

      Step 13: Pressure Guage

      For the pressure gauge, attach a long (1.5m to 2m) length of wood to a sturdy base.

      Position a small bottle about 80cm below the top.

      Drill two holes in the cap of the bottle. Glue two clear tubes to the cap, one with enough length to reach the bottom of the bottle and one that will be just below the level of the lid.

      Fill the bottle about 2/3rds full and fit the cap making sure the lower tube goes to the bottom and the upper tube stays above the water line.

      Run the tube in the water under the bottle and then up the front of the stand in a straight line to the top, use tape to fix it to the stand.

      Where the water level settles mark as 0cm water.

      Make 10cm markings all the way up the stand until you get to 70cm, at this point tape the tube and cut off any excess.

      The other tube can be used to slip under the mask and measure the pressure of the ventilator as it is working - the water level will rise and fall during inspiration and expiration.

      Step 14: Calibration

      To help with the correct tidal volume administered you can draw lines at set interval along the support beam which line up with the bag support structure. To calibrate these lines perform the following procedure:

      • Remove the mask from the end of the air tube.
      • Place a plastic bag around the now open tube and wrap a rubber band or tape around it to stop air leaking out.
      • Ensure there is enough of the plastic bag still able to be inflated to about 600ml.
      • Cut the top of a 2ltr bottle of get a measuring jug with a capacity larger than 1ltr.
      • Place the container into a large Tupperware or something to catch over-spill.
      • Place the deflated bag into the container and use a piece of wood to hold the pipe at the bottom of the container, otherwise it floats to the surface.
      • Fill the container (bottle or jug) to the brim, I used the bucket first and then the measuring jug - fill the container until the water is just about to spill over the edge.
      • Move the bag support to a position on the support beam and allow the cam to move from zero to maximum compression.
      • This will inflate the plastic bag and the displaced water will over flow the top of the container, this is ok
      • Pour the over-spill water from the Tupperware into the measuring jug and record the amount in ml - this is the amount of air delivered.
      • Mark the position of the bag support on the support beam and write the volume of air displaced at this position.
      • Repeat this for a number of positions between maximum and minimum movement of the bag support along the support beam, be sure to do maximum and minimum and at least 3 steps in between.