In the medical device industry, there is an increasing demand for sleeker, smaller designs and speed to the marketplace with the latest and greatest products. Engineers tasked with designing and creating respiratory equipment such as ventilators and anesthesia machines have a host of critical challenges in front of them. End-users demand top performance and compliance with ever-changing regulatory standards. Original equipment manufacturers (OEM) have to meet these challenges by making machines that meet design and performance expectations while also keeping costs down. To do this, source parts and materials must meet the needs and help expedite the design process.

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A direct proportional flow valve provides precision control for the flow of gas within these machines. They are integral to the design of a ventilator and inspiratory flow system.

Valve Functions

In any given machine, there can be up to a dozen proportional control valves. They usually reside in the middle of the system somewhere and provide flow control of the gasses and prevent the over-pressurization of the lines. The valves and many other components within the machine are safety and control elements because they keep the gasses flowing at the desired level.

Considerations When Choosing a Proportional Valve

When choosing a control valve, use the design and application specifications. These are general guidelines and by no means follow a one-size-fits-all solution. The designer of said machine knows what will work best for the specific application. This is merely a guide.

Compliance

It’s important to select a valve that meets the most recent guidelines, laws, rules, and regulations relating to the manufacturing of medical devices. The rules are constantly changing to improve the equipment, so make sure the valve you select meets all the standards.

Air Source

Most operating room and emergency room ventilators use hospital supplied, plumbed air that is prone to significant fluctuations in air pressure. A proportional valve will control these fluctuations and keep the airflow balanced. Depending on the specific application, a high-pressure proportional valve can eliminate the need for a pressure reducing regulator.

We offer valves that accurately control flow in ventilator applications, which require high flow rates of oxygen and air with relatively low supply pressures. Our High Flow Proportional Valve can meet this high flow requirement using pressures supplied by plumbed air in hospital lines, which need to be regulated to a lower pressure to maintain stability in the pressure supply to the ventilator. Our High Flow Proportional Valve can deliver flow rates of over 300 liters per minute with a supply pressure below 2 PSIG.

Hysteresis

A vital consideration with any proportional valve design is hysteresis, a varying of flow at any given setpoint when increasing or decreasing flow. An example of a typical flow curve with hysteresis is shown below.

This variance in flow at a given setpoint due to hysteresis can cause control problems for applications requiring accurate flow control. Our valves offer very low hysteresis, with percentages as low as 2% (of full scale). Our Low Hysteresis Proportional Valve is a perfect fit for systems that require low hysteresis.

Device Size

The trend in machines of any kind, not just medical devices, is to make them smaller. Smaller systems are in demand, and employing a proportional valve with pressure regulation can reduce the number of components needed within the machine to control the flow. Fewer components in the machine mean the machine itself can be smaller.

Kelly Pneumatics offers small, lightweight proportional valves which deliver relatively high flow rates. In particular, our High Flow Miniature Proportional Valve can supply over 100 standard liters per minute (SLPM) of gas flow and only weighs a quarter of a pound.

Gas Compatibility

A certain calibration is necessary for each valve to accommodate a specific kind of gas. Careful selection of control valves with compatible elastomers is important when dealing with anesthesia applications. Our valves come standard with three elastomer types: Viton, EPDM, and Buna-N, but we can customize the elastomers to meet the most demanding applications. The valve material itself can also be modified to other metals – such as stainless steel – to handle even corrosive gases and liquids.

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Additional resources:
How does a Decompression Control Valve work?

How To Choose A Proportional Valve For Medical Devices

Choosing a valve for medical devices is crucially important in facilitating quality patient care. The correct valve can make the difference in providing life-supporting treatment or causing problematic complications. Solenoid valves are typically used for medical devices because they can moderate gas flow with precise speed and accuracy to support patient care. When used in the delivery of oxygen, for example, the valve is used to achieve the correct concentration of gas, and to control the rate of oxygen flow to the patient.

Consisting of an electric coil which surrounds an iron core, a solenoid valve is powered using electricity. It converts this electrical energy into a linear motion, opening or closing the valve, thereby enabling medical personnel to precisely control the flow, direction and pressure of fluids or gases.

Proportional Valve Overview

Medical solenoid valve applications demand high accuracy in terms of force and stroke. They come in several configurations which can be used to act as a shut off, or to allow for two paths of flow. A dialysis machine, for example, uses two solenoid valves acting in tandem to control blood flow during the cleansing process.

While most valves operate in a simple on/off state, a proportional solenoid valve is a precise variation which provides a change in output in the same ratio as the change in the input. If the input doubles, for example, then the output will double as well. In a medical environment where plumbed air is provided, there can be troublesome fluctuations in air pressure which might cause equipment malfunctions.

A ventilator, for example, requires a high flow rate of oxygen and air, but often relies on the relatively low supply pressure of the plumbed supply. The proportional valve is used in these situations to control fluctuations, and maintain a balanced airflow for the patient.

Humphrey‘s Life Science Group offers solutions for oxygen concentrators, respiratory devices, and diagnostic devices.

Proportional solenoid valves regulate flow rate by varying the position of the valve plunger. Typical medical applications where a proportional valve is used to deliver precise performance in pressure or flow applications might include:

• Delivering anesthesia during surgery
• Mixing and controlling delivery of ventilator and respirator gases
• Oxygen concentrators
• Positive End Expiratory Pressure (PEEP) to maintain pressure on the lower airways at the end of the breathing cycle
• Shock wave therapy
• Surgical instruments
• Patient monitoring devices
• Medical mattresses

Variable control methods offered by proportional valves include:

• Dynamic Control: This is used when continuous high-frequency adjustments are required.
• Incremental Control: Appropriate when there are pre-determined, low-frequency adjustments required within each cycle.
• Selectable Control: Allows for selected output flow per cycle, as needed.

Humphrey‘s Life Science Group offers solutions for oxygen concentrators, respiratory devices, and diagnostic devices.

How To Find A Proportional Valve

Proportional valves are used in the medical device sector because they offer the right capability range, and adequately serve most medical device applications. Variables involved in choosing a proportional valve for medical devices include:

• Device Specifics: What type of device needs a valve? What does it do for the patient? How big is it? Does it need to run continuously, or for specific periods of time?
• Medium: The requirement for liquid or gas to flow through the valve will be an influencing factor in setting valve construction criteria.
• Variables: A proportional valve can control many variables, such as force, pressure and flow. Specify exactly what the valve will be expected to accomplish.
• Adjustment Periods: Some systems require constant flow and pressure while others change quite frequently, which requires more adaptations on the part of the proportional valve. A ventilator requires constant adjustments to produce the appropriate gas mixture for delivery to the patient.
• Pressure: Consider the incoming pressure source, and maximum controlled output pressure requirements.
• Flow: Required flow range for specific medical application.
• Temperature: Ambient temperature requirements.
• Power: Look at power capabilities, especially in terms of mobile or portable applications.
• Environmental Factors: What is the location of the medical device? Are there any space or weight constraints? Is portability a requirement?
• Compliance: In the medical field, there may be special requirements related to medical devices in order to comply with FDA or other regulatory requirements.

While some medical devices are constantly monitored, others are expected to perform consistently and reliably on an autonomous basis. Proper proportional valve selection is crucial for their operation. Contact JHFOSTER today to receive information and guidance from our team of experts, and let one of our certified technicians walk you through deciding which proportional valve is right for your specific medical application.

Headquartered in Eagan, Minnesota, JHFOSTER provides a wide range of reliable pneumatic valves for an array of applications. The JHFOSTER team can be your partner in choosing the right components, in the right systems, for your specific medical device applications. Contact us online, request a quote, or call 855-688-0043 today to discuss which proportional valve is best suited to your medical device needs.

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