Many medical devices require precise pressures and flow rates. One example application is for ventilators—something that we all became very familiar with in this COVID pandemic era.,

In a Medical Product Outsourcing article, Proportional Valves in Medical Devices, Emerson’s Paul Gant describes how proportional pressure control valves help to meet the stringent requirements for medical devices including:

• Anesthesia and ventilator gas mixing
• Ventilator patient “delivery” valve
• Leak testing — Medical components and packaging
• Positive End-Expiratory Pressure (PEEP) control
• Oxygen concentrators
• Patient simulators
• Shock wave therapy
• Surgical instruments and patient monitoring
• Clinical diagnostic equipment

For manufacturers of these medical devices, they must consider:

…both the medium and variable to be controlled. Gas (air, oxygen, CO2 or others) is usually the medium, and a proportional valve can control many variables, including force, position, temperature or level.

Paul focuses this article on pressure and flow requirements. Criteria for valve selection include:

• Medium, which will influence required valve construction or materials
• Inlet pressure and maximum controlled output pressure
• Required flow range
• Media and ambient temperature
• Other environmental factors, such as location (hospital, clinical or portable) and any weight or space restrictions
• Power consumption, especially for portable/mobile applications
• Special requirements related to medical devices to comply with FDA or other regulatory bodies’ requirements

For many of these constantly changing flow and pressure applications, they:

…require the setpoint to change frequently, causing the valve to operate by varying its opening size continually in response to an often-changing command signal.

Types of proportional valves used in medical devices include the most popular direct-acting proportional solenoids as well as pulsed, air-piloted and motor control.

Direct-acting proportional coil valves act directly on pistons or spools to adjust valve opening positions based on a varying current across the coil. These valves offer advantages over piloted valves as they may fit a considerably wider range of applications and provide simpler construction with fewer mechanical parts, simpler principles of operation and more dependable performance capabilities.

Proportional pressure control typically:

…includes two valves, a pressure transducer and an electronic controller. The electronic controller serves as the brains of the unit, allowing a setpoint to be provided by the user and comparing/controlling the results such that the valves act in a way to quickly achieve the desired result.

The AVENTICS Sentronic Plus (Series 614) proportional pressure control valve with integrate IO-Link with integrated digital control loop combines the latest in pneumatics technology with intelligent electronics. Digital pressure control is a closed loop. An internal pressure sensor measures the outlet pressure and this outlet pressure is adjusted in real time. This closed-loop control allows for precise control of pressure, flow, force, velocity and displacement or angle positions.

Read the article for more on how this valve can be configured for single loop or cascaded loop control and how other proportional valves are available to meet the stringent requirements in these medical device applications.

Visit the Medical and the Fluid Control & Pneumatics sections on Emerson.com for more on the technologies and applications to improve the safety and reliability of medical devices. You can also connect and interact in these groups in the Emerson Exchange 365 community.