Gas and liquid valves are used throughout the medical device industry, in major part due to their automated functions, along with their excellent reliability and long life. They are used to control the flow, direction and pressure of gases (oxygen, for example) or fluids (including reagents and other aggressive or non-aggressive media) being used by a device. Air and oxygen valves, as well as liquid “isolation” valves commonly used in medical and diagnostic devices must also meet stringent regulatory requirements to assure compliance with FDA, CFDA, MDR amongst other standards demanded in this field.
The analytical and medical industry has a constant demand for high-performance devices that leverage advances in areas such as material sciences and electronics to improve device performance, longevity and dependability. Miniature valves, and the electronics that control them, are widely utilized to satisfy this demand. Some examples of these medical device applications are oxygen concentrators, ventilators and respirators, anesthesia equipment, patient monitors, clinical diagnostics, DNA sequencing, surgical equipment, and even dialysis.
Recent improvements in many solenoid operated valves are helping medical device manufacturers use energy much more efficiently, allowing them to build more compact and portable equipment and manage issues such as heat generation more effectively.
Solenoid Valves Reliability
Solenoid operated valves are commonly used in oxygen therapy devices because they offer the design engineer value and reliability and provide excellent functionality. The engineer can combine smart electronics with the valve to enable automated functions to automate and improve the machine.
Pressures in medical device applications are often lower compared to more industrial applications — often 1 bar (14.5 psi) and much less — although some devices, such as ventilators, can also require valves to mix air and oxygen with input pressures at 2 bar or higher. Proportional control, or the ability of a valve to vary its orifice size based upon the strength of a signal, gives further capability, and has multiple uses. An electronic proportional valve can be used to control the mixing of the gases prior to patient delivery, vary the amount of oxygen/air mix to the patient, and even control the residual pressure in the lungs during exhalation. Combined with a ‘smart’ electronic control system, these valves can give the design engineer the best tools to deliver exacting solutions for the patient in need of oxygen therapy.
In addition to the ventilator functions just described, miniature solenoid valves can periodically “auto-zero” the device’s pressure transducer (to assure that the machine is calibrated to the proper altitude and atmospheric conditions), add therapeutic gasses, control the maximum pressure and flow delivered to the patient, and even as a ‘relief’ to safely guard the patient. Depending on the type of device, valves may also perform different valuable functions to maximize the capability of the specialized functions of that machine.
Isolation Valves for Control of Fluids
Isolation valves are used where the control of fluids must be accomplished with efficient precision and leak-free operation. These applications most times differ from gas control, in that the fluid must be contained, and often must be controlled without contamination from outside elements; even the solenoid valve itself. Often, a membrane is used to accomplish the isolation, with many different design elements and functions for the unique application. An alternative design is pinch valve control, where a fluid flows through a soft tube, and the pinch valve accomplishes on-off, directional or proportional control of the medium by ‘pinching’ the tube. In this case, purity of the medium is assured.
In addition, pressurized gas may be used to control a liquid, such as pressure or volume control in an infusion pump for nutrients/drugs, or to accurately meter media in diagnostic or research equipment. Contamination is eliminated with isolation designed into the instrument.
The design engineer for systems controlling fluids often looks for a manufacturer with an extensive portfolio consisting of gas and liquid valving, along with manifolds and accessories suited specifically for the analytical and medical fluid-handling sector. Better yet, valve manufacturers’ extensive engineering capabilities and application expertise today support some of the world’s leading analytical instrument and medical device OEMs, ranging from clinical diagnostics to DNA sequencing; from oxygen therapy to medical support surfaces (i.e. hospital and other specialty-function beds).
Current and Future Trends
There are several technical advantages solenoid and other miniature valves offer medical device designers, as well as some key factors to consider in choosing the right component, based upon a device’s required functionality and usage. These include:
- Power management
- Integration of electronics
- Data acquisition
- Custom design support
Lightweight and Compact
One of the leading reasons solenoid valves and other miniature fluidic components have long been used in medical devices is that they combine lightweight construction with a simple, compact design to enhance medical device portability — a key requirement across many applications.
In other examples, one area that has been recently improving in solenoid valves technology is the ability of manufacturers to custom-configure standard solenoid valves components to fit more readily into tight device configurations, to reduce weight without sacrificing functionality. These advances continue to be driven by the needs of patients, healthcare organizations and medical device manufacturers.
Solenoid valves are electrically powered, leading to two key design considerations: power consumption and heat control. An advantage the most recent generation of solenoid valves offers is that they are typically available in a broad range of power profiles: If a 3.3 volt coil is best fit for a particular valve, it is usually available as a standard variation.
This means designers can better match the solenoid valve to the power capacity of the medical device, which can help extend battery life on portable devices. It can also help control the heat generated within the medical device: For equipment such as blood diagnostic machines, minimizing excess heat is crucial to prevent samples from being altered or contaminated and incorrect results being reported.
The compact, simple design of many solenoid valves makes them especially useful for manufacturers who are developing new models or equipment in pilot projects and need to be able to scale up (or down) the production run of the end product, depending on market demand and healthcare community support.
Solenoid valves can be easily integrated into manifolds and other electro-pneumatic control sub-assemblies, whose production can be cost-effectively scaled-up. For example: A surgical tool manufacturer recently developed the prototype of an ultrasonic aspirator used in conjunction with a grinding instrument. The device functions by first flushing the incision area then vacuuming blood and bone or tissue fragments through a handpiece.
A pneumatic control sub-assembly incorporating solenoid valves provides vacuum level control and enables selection of either external air sources or on-board vacuum pump. If the device is successful, the solenoid valves sub-assembly circuit and resulting sub-assembly may be easily altered for the best cost at various quantities in production.
Integration of Electronics
Initially, solenoid valves were relatively simple electro-pneumatic devices. However, medical device manufacturers can benefit if the valve manufacture integrates microelectronics into the devices to make them more intelligent and enable them to utilize a variety of digital communications protocols, such as Ethernet IP or Profinet.
Miniature electronic proportional valves, combined with the proper electronic controls and feedback, can control pressure, flow, or other variables in a medical device. These closed-loop systems give the design engineer the ability to design complex system control, yet still rely on the valve manufacturer to provide the most robust tool to accomplish design challenge in a robust, proven, yet affordable package.
“Smart” Solenoid Valves for Therapeutic Outcomes
There has been a strong drive across the healthcare industry to leverage digital information from medical devices to help track and assess patient therapy outcomes — and integrate that data into digital patient records more efficiently. In the near future, the integration of digital technologies into solenoid valves can contribute to this trend.
Digital technology now being incorporated into solenoid valves can be utilized to help document how the operation of medical devices contributes to therapeutic outcomes. Medical device designers can take advantage of these capabilities and use them to provide a competitive edge in their systems’ performance.
For example, each time a solenoid valve is actuated by the medical device’s controller, it can send back a response in the closed loop, confirming the valve’s sequence. For example: A patient in surgery is on a respirator, which supplies a mix of air and oxygen during the procedure. The respirator has an oximeter which continually measures the level of oxygen in the blood; if the level drops below a preset, the system automatically sends a signal to a solenoid valve to adjust upward the level of oxygen being supplied.
In this scenario, an intelligent solenoid valve would communicate back through the control loop the valves’ actuation and how much the level of oxygen was increased. This information can thus become part of the digital record of the patient’s treatment, ultimately helping to ensure medical devices such as ventilators, portable oxygen concentrators, dialysis machines and drug delivery devices are properly providing the targeted therapy.
Benefits of Custom Design Support
Many suppliers of miniature gas and liquid control valves have standard product portfolios. However, given some of the unique design challenges medical device manufacturers have — portability, energy efficiency, scalability and use of digital data — it can be beneficial to work with suppliers who can develop more custom solenoid valve configurations to meet unique requirements.
This includes working with suppliers who have engineering resources available to quickly adapt standard products to custom configurations (valve size, pressure, weight, etc.). Familiarity with integrating electronics into miniature control solutions and experience integrating solenoid valves into complete sub-assemblies is also a desirable capability, to help meet desired functionality and cost targets.
While the miniature solenoid valves could be called relatively “simple” in their core technology, continued investment in their evolution makes them valuable and effective components for controlling the flow, direction and pressure of gases and/or fluids in today’s medical devices.