How to Select Seal Materials for Medical Ventilators
In the rush to massively increase the number of ventilators available to treat patients with severe cases of Covid-19, using the correct seal materials for those ventilators should never take a back seat to expediency.
Patient ventilators are mechanical devices that essentially breathe for a patient with damaged lungs. They force air into the lungs and draw it out, augmenting or even replacing the natural functions provided by the movement of the diaphragm and the inflation/deflation of the lungs themselves. These devices can supply room air, pure oxygen, or nearly any ratio of the two to the patient, depending on health needs.
What makes a good seal selection in this environment?
First, seals within the device must be compatible with air and pure oxygen. They should not harden or crack, nor should they contain a significant amount of volatile matter that can evaporate out of the seal where it could be inhaled by the patient or potentially catch fire in a concentrated oxygen environment. Further, it should be assumed that any air that contacts the seals will likely end up in the patient’s lungs. As a result, Parker strongly recommends using seal materials that have passed USP <87> Class VI testing for any seals used in a ventilator.
Parker O-Ring & Engineered Seals Division has already helped several customers ramp up production of critical medical equipment with supplying the right materials and O-rings for the application.
These application requirements limit the recommended compounds to only a small handful.
Recommended compounds suitable for use in ventilators
Parker’s silicone compound S1138-70 is an excellent first choice for many ventilator seal applications. It has low outgassing, it has been tested to and passes USP Class VI, and it’s completely compatible with air and pure oxygen. In addition, silicone is also naturally non-flammable – even self-extinguishing – so it offers no fire concerns. However, abrasion resistance is poor, so it should not be used in a dynamic application. In addition, permeation resistance is also poor, but pressures in a ventilator are low enough that this small amount of air or oxygen loss is usually negligible.
Parker’s EPDM compound E3609-70 offers similar compatibility and outgassing with much better abrasion resistance and improved permeation resistance when compared to silicone. It is also less prone to pinching and tearing upon assembly than silicone. E3609-70 has also passed USP Class VI and performs well in air and oxygen. As a result, it is recommended for dynamic applications such as seals on moving shafts. EPDM polymer will burn under the wrong conditions, but this is not usually a real-world concern for ventilator applications.
Caution should be exercised with Parker’s E1244-70 compound. While the combination of passing USP Class VI and internal lubrication may seem attractive for reducing friction in dynamic applications, these internal lubricants are organic molecules which can be flammable. When deposited in a thin film on mating surfaces as in a dynamic application, they could ignite when exposed to oxygen. This should be tested prior to use to ensure it does not cause a problem in application. In general, it is safer to use a non-flammable liquid lubricant such as silicone or perfluorinated polyether (PFPE) oil or grease to reduce friction in dynamic applications. Parker’s Super O-Lube is a pure silicone lubricant, but it has not been tested or approved to any medical device specifications.
Finally, Parker’s fluorocarbon compound V0680-70 offers an interesting balance of properties. While it is not as good for abrasion resistance as an EPDM, it is still much better than any silicone. Like silicone, it is self-extinguishing and fully compatible with all combinations of room air and oxygen. Permeation resistance and outgassing properties are outstanding. V0680-70 has been tested and passed USP Class VI and is the same rust color as most silicone rubber compounds.
Prioritizing medical equipment
During this time of crisis, Parker is prioritizing production of seals needed for critical medical equipment, and these four compounds in particular are strongly recommended for use in ventilators. They offer excellent long-term compatibility with room air and oxygen, have low outgassing, and have all passed USP Class VI testing. Learn more about the solutions available.