14 April 2020

By Armand Bergsma (edited for updates on May 8, 2020)

On March 16, 2020 – shortly after the Dutch government implemented its so-called “intelligent lockdown” and while we were busy figuring out how that would impact our business and operations – PCS was contacted by a student who was part of the TU Delft project group “OperationAir”, requesting a pressure controller for low pressure. The device was intended for application in a prototype ventilator. Read more about how OperationAir was put together by TU Delft professor technical medicine Jaap Harlaar and the inspirational commitment of the project group on their website.

How Pressure Control Solutions was challenged to step in

Right from our first phone call, it was clear that this group was determined to get the job done; their enthusiasm was overwhelming and inspiring – it gave hope and positive energy in the middle of the increasing concern and gravity of the corona pandemic. Pressure Control Solutions was eager to commit to this great initiative, contributing with both knowledge and ideas as well as products we had on stock for direct delivery, such as pressure controllers and mass flow controllers. This facilitated immediate brainstorming and protoyping.

Medical ventilators and pressure control requirements

Obviously, our contribution focused on the challenge to arrange for pressure control under demanding conditions: How to generate a safe and reliable breathing mechanism for a human patient in comatose state?

After some testing with a dual valve pressure controller containing a pressure sensor, PID controller and two proportional valves, it turned out that cascade control based on a pressure sensor close to the patient was not fast enough to get a clean breathing cycle. The team then decided to take the pressure controller apart and started to control the upstream proportional valve directly from an Arduino control board. This approach worked out well, resulting in a request for a pulse widt modulated (PWM) proportional valve. The plan was to mix O2 and Air by using 2 mass flow controllers (supplied by our supplier Bronkhorst High-Tech, NL) and to place a buffer tank downstream of the mass flow controller, therefore the proportional valve should work with a varying inlet pressure between 200 and 900 mbar. The pressure to be controlled inside the patient’s lungs would need to be between 5 and 50 mbar gauge.

Product development: Designated valve for use in the AirOne ventilator prototype

We developed a valve specifically for this application and parameters, with the caveat that we are not a supplier of medical devices or even existing components currently used in the medical device industry. In this case, the customer team assumed all design responsibility and requested our further development of a ventilator valve for their prototype – by now known as the AirOne prototype – anyway.

We developed a prototype valve with a Kv value of 0,35, capable of dosing >50 ln/min of air with an inlet pressure of 100 mbar. For the body, we used stainless steel, combined with an actuator supplied by a supplier we were already familiar with through other products. We used FDA-approved sealing and a FKM grade 90 plunger, handcrafted by PCS from commercially available O-rings. The prototype has been delivered to OperationAir on the 2nd of April, less than 3 weeks after OperationAir  initially contacted us. The prototype turned out to be plug-and-play, resulting in a request for a 2nd prototype.

From prototype to production?

The prototype is currently subject to clinical testing. There is a fair chance that the emergency respirator will be taken into production soon. Pressure Control Solutions is ready to produce this valve in larger quantities. Given the large current need for respirators around the world, OperationAir has announced that all design information and bill of material will be made available on their website for the benefit of similar initiatives in other countries.
Edit May 8, 2020: The design information has now been made available to the public on this page.

Do you have pressure control issues related to medical applications?

Although the valve developed for OperationAir is not a standard, commercially available product in its current state, we welcome any additional requests for knowledge sharing or prototyping related to pressure control aspects in ventilator design. Please contact us if you wish to present us with your approach and the pressure control aspects you encounter.