Designers achieve faster development time and maintain better control and consistency over their instrument package when they are able to focus on
their main priorities, such as chemistry, software and assay
development. Specialized vendors can take on the role of
optimizing their optofluidics—optics, fluidics, microflu-idics—however, the industry should work more collaboratively with customers, sharing expertise and knowledge
wherever possible along the way.
For fluidics, the need for highly precise fluid control
and delivery is paramount, particularly with the increasing application of biological reagents, the analyses
of extremely small samples, and the desire for high
throughout and minimal carryover. Achieving these goals
within a flow path with little resistance to fluid flow and
a high degree of control requires significant expertise.
For many automated fluid control applications, rotary
shear valves coupled to manifolds are a favorable choice
for the instrument designer—used for tasks such as solvent selection, flow switching and injecting samples into
flowing streams. Rotary shear valves have been the backbone of the chromatography industry for many years,
due to their cleanly swept internal volumes and ability
to handle larger pressure ranges than similarly-sized solenoid, spool, plug or pinch valves.
Selecting the right valve
Selecting the right valve for your specific R&D needs is
a specialist skill. The priorities set out for valve selection should include:
Priority 1—Groove pattern. The first priority is to
choose a valve based on its rotor groove pattern. This
defines what the valve will actually do in a fluidic circuit, along with the rotor indexing.
Priority 2—Pressure rating. Selecting a valve according to its pressure handling capability is the second
priority. Valves rated for too low a pressure than required in a fluidic circuit could get damaged or leak
under higher pressure conditions. On the other hand,
valves that are over-rated for pressure can possess small
passageways that are too restrictive at high flow rates
when used in a fluidic application.
Priority 3—Valve geometry. There are a number of
connection options that are available for the design
(fitting, tubing or manifold). Some designs use compact ferrule clusters to make connections, some designs
adapt readily to manifolds, while others utilize a set of
industry standard Metric or Imperial fittings to connect
to other devices. The choice of connection will often
dictate how user-friendly or serviceable a specific instrument is in its final form.
Priority 4—All other differentiators. After we have
selected valves based on function, pressure handling
and geometrical concerns, valves can further be differentiated according to the materials they are composed
of, the footprint of the actuated valve, wetted materials
or designer familiarity, among a host of other criteria.
Now you have selected the most appropriate valve for
your work, here are some top tips for valve optimization:
• Be aware of the chemical compatibility of all
the reagents used in your system, and make sure
you test them against a real life valve during the
validation of your equipment.
• As you design your fluid path, be aware that rotor grooves pass by adjacent ports in the stator as
the rotor sweeps through its trajectory. Make sure
you do not accidentally let gravity or pressure mix
fluids that should not be getting mixed.
Selecting the right valve for your
specific needs is a specialist skill.
By Darren Lewis, Ph.D., IVD/Bio R&D IDEX Health & Science LLC
Anatomy of a rotary shear
valve (Actuated Titan HT).