Engineers in the design of medical devices find electronic proportional valve technology suitable when precise performance is required in flow or pressure variable applications. It is often viewed as more complex than solenoid valves that operate on/off and proportional valves. They offer reliable and cost-effective solutions that provide quick response and constant control. A few typical proportional valve applications within the medical field comprise:
- Mixing ventilator gas and anesthesia.
- Ventilator patient “delivery” valve.
- Leak testing -medical components and packaging.
- Control of Positive End Expiratory Pressure (PEEP) control.
- Oxygen concentrators.
- Patient simulators.
- Shock wave therapy.
- The use of surgical instruments and monitoring for patients.
- Diagnostic equipment for clinical use.
Today, many proportional valve manufacturers are designing valves by keeping all these requirements in their minds.
When choosing an electronic proportional valve when designing a medical device, the engineer must consider both the variable and medium control. Gas (air or oxygen, CO2 or other) is the most common medium. An electronic proportional valve is able to control a variety of variables, such as force, temperature, position, or level. However, in this post, we’ll concentrate on the two main aspects of flow and pressure. Once the engineer who designed the valve has determined the variables that require control, determining the other requirements to the valve(s) is next, for example:
- Medium, which will affect the construction of the valve or the materials.
- Maximum output pressures are controlled.
- The flow range that is required.
- The ambient temperature and the media.
- Other environmental elements like the location (hospital, clinic, or portable) and any restrictions on weight or space.
- Consumption of power, in particular in mobile and portable applications.
- Medical devices that are required to meet FDA or other regulators’ requirements.
Constantly Changing Pressure and Flow:
In general, all of the above scenarios need a continuously changing control of pressure or flow (with the exception of the leak test that generally requires a predetermined pressure to be maintained continuously (and later, quickly adjusted to a different setpoint for testing later or for an entirely new item or package to be examined).
Continuously changing pressure and flow requires the setpoint to change frequently, which causes the electronic proportional valve to work through a change in its opening continuously according to a frequently-changing command signal. One example is the ventilator or anesthesia gas-mixing circuit where the output of three or more valves is continuously adjusted to provide a certain mixture of gasses. The gas mix is given to the patient as per the specifications for the machine. Other aspects could include changing pressure levels in the device for shock wave therapy. Pressure within the system is adjusted to alter how much “strength” the equipment produces the shock wave. These devices that generate shocks require robust proportional valves that can meet the ever-changing demands for flow and pressure within their systems.
Types of Proportional Valves:
Various operating techniques are employed in the field of proportional valves. The most well-known valves for the medical device industry are direct-acting solenoids, as they have the best spectrum of capabilities and can be used in all medical devices. But, different methods of actuation can be employed to provide the control needed in certain applications, such as air-piloted, pulsed, or motor control. One type of electronic proportional valve that operates directly is the piezoelectric model. This valve transforms the piezoelectric component to alter the valve’s opening when the voltage is applied. Piezoelectric valves are utilized when a common power source is required (portable device) or when the device requires extremely low-temperature generation, like in many diagnostic types of equipment for medical use.
Direct-acting proportional coil valves work directly on spools or pistons to adjust the valve’s opening position depending on the current that flows throughout the coil. These valves have advantages over pilots since they can be used in a greater variety of applications and simplify the construction process with less mechanical components, simpler operation principles, and more stable performance capabilities. Direct-acting air-actuate valves last longer during high-speed operations where valve are used more frequently. Their sturdy construction eliminates the risk of wearable components failing. They are also less susceptible to air contamination or gas media.
Other advantages of technology include the ability to decrease overshoot. That is the tendency of valves to speed up towards the setpoint but then speed over it, then return to its setting point, and possible overshooting. This happens frequently when system are turn to provide rapid response times. The oscillations usually have a shorter time to settle indirect-acting proportional coils because the valve can move. The piston by varying the current flowing on the coil. Direct-acting proportional coils usually provide precise control of the pressure. This is crucial for leak test applications, which require an extremely steady pressure throughout the testing process. This type of proportional air pressure control valve can react to tiny setpoint adjustments and make precisely precise pressure changes. In general, the direct-acting model is more responsive, speedy, and resolution. Making the valve superior to air-piloted designs for various applications.