Friday, November 16, 2007
Here is a link to a very good commentary on the potential of shortage of ventilators in an Avian Flu Pandemic.
Friday, November 9, 2007
Here are some details of how the Pandemic Ventilator is constructed.
It basically consists of the bellows unit, which is made of wood, valves and piping, a PLC controller, some wires and switches and a power supply unit.
The whole unit is mounted on a piece of ½ inch thick that is plywood 18 inches by 21 inches.
To get started you will need the valves. You may be able to find some used ones somewhere. New valves are expensive, over $100 each. The inlet valve can be ¼” normally open valve, the other two should be a minimum ½” diameter, one normally open (NO) and the other normally closed (NC). They must be of a direct acting solenoid type.
Direct acting solenoid types are required to operate with air. Pilot operated types will only operate with liquids. Pressure ratings do not matter for the 1/2'' valves, but the 1/4' valve should have at least a 50 psi rating. If you can only get either NO or NC 1/2" valves you can still make it work by adjusting the PLC output. The inlet 1/4' valve must be a NC valve or you will end up blowing up a lot of bags in the testing phase.
The valves are connected with pipe and mounted in such a way that the “T” to the Bellows lines up with the center of the bellows unit.
I used threaded pipe fittings. I used:
- Two ½” NPT “T”s, One ¼” airline fitting (to connect to an air supply)
- Four ¼” pipe nipples (short pipe sections threaded at both ends)
- Three ¼” to ½” adapters
- Two ½” pipe nipples
- One ½” plug
- The bellows unit has a hinged section of ¼ inch plywood that is 10 ½ inches by 12 ½ inches.
- There is a 1 and a 1/2” by 1 and a 1/2” by 9” sensor pole attached beside the bellows that is used to position the magnetic switches. It should be angled at the bottom so that the top leans back about 1and ½ inches from the bottom.
- The bellows hinge is constructed of 4 pieces of 1 and a 1/2” by 7” 5/8” plywood pieces and one 1 and a 1/2” by 1 and a 1/2” by 17 inch piece of wood, two 3” hinges and a 2” by 12 and a ½” reinforcement.
- The bellows is made by screwing down the bottom 2 plywood pieces to the backing board.
- Arrange the other 2 plywood pieces directly over the first two, cover with the 17 inch piece of wood and and clamp together.
- Drill holes centered 2 and ¾” in from each end to accept ¼” carriage bolts inserted from the bottom.
- Unclamp and remove the top 17” piece of wood.
- Insert carriage bolts from the bottom to line up the middle layer plywood pieces and clamp again.
- Screw hinges to middle layer plywood. Ensure the screws do not protrude through the plywood to the bottom layer.
- Screw the other side of the hinges to the bellows lid between the lid and the reinforcing strip.
- The bag is clamped between the two plywood sections during operation using the nuts and washers on the carriage bolts.
- The magnet is attached to the end of the bellows near the sensor pole, and the sensors are attached to the sensor pole.
- Cut off the ziplock part.
- Inert ½” plastic tubing into the center and use Tuck tape to seal and reinforce the edges.
- The tubing should stick out of the bag far enough to be able to be slipped over the end of the ¼” nipple section of piping.
- The taped seam of the bellows bag should be in on the bottom plywood section.
- Install the hinged cover and then the top 17” section.
- Clamp together with the 4” long ¼” carriage bolts, two nuts and 2 washers.
- The valves, sensors, switches and power supplies are wired to the PLC unit.
- Wiring diagram and program will be posted later.