Leak rates
- Pressure will directly affect the leak rate. The higher the system pressure, the higher the potential leak rate — a higher-pressure rating means better leak rate.
- Surface finishes are essential in guaranteeing a low leak rate. Elastomers have specific leak capabilities due to material porosity/void fraction and permeation.
- Ability to be analytically cleaned. The analytical cleaning process is essential to ensure the valves do not introduce background or any contamination into the sample stream.
- Seat and seal load are determined by the system forces and sealing surface quality.
- Coil power consumption or coil force determines the spring force and pressure that can be applied to the valve. Valves with the same total power consumption can have different leak rates due to design, maximum designed pressure capability, orifice size, and magnetic materials.
Reliability and repeatability
When selecting valves in POCT instruments, reliability and repeatability are of utmost importance. For a valve to have repeatability, it needs a long-life cycle, high yield rates and a proven track record. When determining reliability in a valve, you must evaluate the design, quality of material, and manufacturing process, and controls of the product.
Power requirements
POCT instruments are designed to operate in non-laboratory conditions. This means that the instrument needs to be designed to function using the power available from a standard wall power outlet. Where multiple valves and other components can be demanding power simultaneously it is important that the total amount of power being consumed does not exceed the power rating of the wall outlet. Selecting valves designed to use less power is an important first step. Another way to reduce overall power is to use hit and hold circuits. Hit and hold circuits allow valves to be fully powered and remain in that state for a short time before voltage and current are reduced to lower levels, while still allowing the valve to remain energized. This procedure allows the valve to stay open with much less energy. This also allows the valve to generate much less heat and decreases the power draw. This type of circuit option in a valve reduces heat, increases cycle life and lowers energy consumption — an ideal solution for original equipment manufacturers (OEMs).
Wetted material
Materials used in valve construction are crucial for valves with critical leak requirements. The term wetted material is important to understand. The wetted material is defined as any surfaces and/or components that are (potentially) exposed to or in direct contact with the medium under pressure. A few more important things to know before selecting a valve are permeation rate, compatibility with certain fluids (specifically what your system uses), and potential out-gassing that can occur.
Subsystems
Finally, look for the availability of subsystems. A subsystem is a pre-assembled module that includes tubing, fittings, regulators, valves on a manifold, and other accessories.
The benefits of a subsystem include:
- Eliminates the need to maintain multiple vendors
- Reduces the overall bill of materials,
- Provides integration between components, creating one single stream for technical support and customer service.
- Cost reduction in assembly and labor time.
- Modules can come pretested allowing them to be dropped in during manufacturing.
Take a closer look
Let's examine a simplified fluidic circuit used in a POCT system. In this case, we are looking at a molecular diagnostics system. Most POCT designs use pneumatic pumps to provide the energy to move liquids around in the cartridge. This means that compact high-efficiency pumps are critical to reducing overall instrument size.
How it works
Air is controlled precisely by an electronic pressure controller. This pressurized air is fed into a manifold that is a permeant part of the instrument. Valves mounted in or on the manifold then control when and where the flow of air is directed to move the sample and reagents through the cartridge. Several types of valves are typically employed with the critical requirement that they are miniaturized to reduce the size of the manifold and therefore the entire instrument.
Digital or on/off valves are the most common in either a cartridge valve format that is embedded in the manifold or surface mount designs that are mounted on top of the manifold. Cartridge valves can reduce the footprint of the manifold by allowing valves to be placed very close to each other. The drawback is they make the manifold thicker and more expensive. Surface mount valves have a larger footprint on the manifold but can be supported by a thinner manifold design which weighs less and takes less space. Proportional valves can be used where there is a need to vary the flow instead of just turning it on or off. In operation, the various valves open and close at the right times driving the sample and reagents through the various steps of lysis, nucleic acid purification, amplification, and detection.
POCT system solutions
With a broad portfolio of pumps and valves, Parker can offer the optimal fluidic components to meet your requirements. Parker can provide manifolds that are either developed to your drawings or optimally designed by our engineers. A variety of manifold materials are available to choose from.
Parker is proud to be the only company capable of offering a complete product selection by integrating manufactured components and custom assemblies. We are eager to help you with all your precision gas and fluidics needs.
Parker Precision Fluidics has over 30 years of experience in developing valve and pump technologies. Our engineers specialize in helping OEMs update original valves that are producing low yields.
Our applications engineering team is always available to provide recommendations and customize equipment to customer specifications.
Download our application note to learn more about what to consider when developing fluidics for a POCT system
To learn about Parker's point of care testing solutions, please visit our website, or call 603-595-1500 to speak with an engineer.
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