Custom valve varies ventilator flow

A custom valve assembly lets a ventilator meet the respiratory care needs of adults and infants.

The AVEA ventilator from CareFusion, Yorba Linda, Cal., is a critical- care device that supplies precisely metered volumes of air or oxygen to patients who cannot breathe on their own. It differs from traditional units in that it can provide two different flow rates: one for adults, and a lower rate for infants and young children who have more-fragile pulmonary systems.

Because it handles a wide range of respiratory care needs, hospitals no longer need to purchase separate ventilators for large and small patients.

An oxygen supply valve was a critical part of the ventilator design. The valve had to be compatible with medical- grade air and oxygen and capable of delivering flow volumes from 2 ml/ min to 2.5 l/min. And it had to be light and compact, consume little power, and meet specific porting and mounting requirements.

Extremely limited space inside the ventilator eliminated the possibility of using an assembly of standard valves. Because no off-the-shelf product could meet all these requirements, CareFusion designers approached the Engineered Solutions team at Humphrey Products Co., Kalamazoo, Mich.

Humphrey engineers developed a custom valve assembly that would meet the ventilator’s performance specifications, along with a custom manifold to satisfy space, porting, and mounting requirements. They opted for a two-way, high-flow pilot-operated poppet valve assembly with an integral check valve to block flow when the poppet is closed.

Modifying a standard Y500 insert valve overcame space restrictions.

The engineers started with Humphrey’s Y500IN insert valve, but determined that only the top half of the valve – containing the poppet – would fit the space available. That, in turn, required a new way to guide the poppet. “The Y500IN is guided by its extended stem,” explains Matt Brown, of Humphrey. “When you use only the top poppet, you don’t have a sufficient guide to align the poppet with the seat.” The engineering team overcame this problem by adding a skirt to the piston. This increased the surface area and helped guide the poppet into its seat, resulting in smooth and consistent shifting, says Brown.

The product uses oxygen-clean materials, including approved lubricants and EPDM elastomers. A low current, 0.5-W Mini-Mizer solenoid valve was used as a pilot valve. It limits power consumption while controlling the pilot flow of high-pressure oxygen that actuates the insert valve.

Next, they designed a custom manifold, incorporating CareFusion’s q u a l i fied check valve, to provide two different flow rates. The manifold was designed with the valve normally open, supplying the flow volume of air or oxygen required for adults. When the unit switches to the lower-volume “child” mode, explains Brown, the pilot valve energizes, and pressure is applied to the top of the piston. Pressure overcomes the spring force and shifts the piston poppet into a seated closed position. Oxygen now is forced through the special check valve equipped with numerous small orifices. This reduces flow to a rate which is ideal for children and infants.

To facilitate assembly despite space limitations, Humphrey engineers also designed a custom bottom cap. The valve is 100% tested, then delivered in two pieces. The pilot valve, insert, and check valve are mated together, but the bottom cap is not attached when shipped. The cap fits a standard socket wrench and mates to an existing, drilled and tapped 38-in. cylinder port hole. This eliminates the need for special tools and allows CareFusion to tighten the bottom cap, then slide the valve body into place. The valve body then mates to the bottom cap by two screws that extend from top to bottom.

For more information on Humphrey Products Co., visit www.humphreyproducts.com.