Valveless Fluid Control For Medical Diagnostic Instrumentation
Clinical Chemistry and Immunoassay Diagnostic Analyzers
The results of recent surveys suggest that more than half of all healthcare decisions are made using the
test results obtained from medical diagnostic instrumentation. These tests are routinely performed by
diagnostic instrumentation at hospitals, diagnostic centers, and at a variety of “point-of-care” locations.
The results of these tests greatly assist healthcare professionals in the detection and diagnosis of a
broad range of health conditions and diseases.
The majority of Medical Diagnostic Instrumentation are made up of Clinical Chemistry and Immunoassay
Analyzers. Clinical Chemistry tests quantitatively measure the chemical makeup of different kinds of
bodily fluids, most common being blood components (whole blood, serum & plasma) and urine,
although there are clinical tests for many other bodily fluids (amniotic, cerebrospinal, pericardial, and
saliva just to name a few) as well. A variety of different clinical chemistry tests exist to detect and
quantitatively measure almost any type of chemical component in the body including blood glucose,
hemoglobin, electrolytes, enzymes, hormones, cholesterol, lipids, proteins, and other metabolic
substances. Immunoassays basically handle the same bodily fluids and are biochemical tests designed to
detect the level of specific proteins, antibodies or antigens, in a sample. These specific substances are
typically present or elevated as the result of an immunological reaction, manufactured by the body most
often in response to the presence of a foreign protein or micro-organism (bacteria, virus etc.).
Precise, Accurate Micro-Volume Fluid Control
Both Clinical Chemistry and Immunoassay Analyzers detect and aid in the diagnoses of patient health
conditions, and design similarities result in having many functional components in common. Since
samples, reagents, a variety of buffers, wash and waste fluids are in liquid form, there are many fluid
control requirements and components that are essential to both systems. The performance of these
components will have a direct impact on the accuracy of the instrument as well as the reliability of the
information it yields. In addition, manufacturers of diagnostic instrumentation continue to strive to
meet increasing demands to develop analyzers that can perform more and more tests using smaller and
smaller samples. The challenge is to maintain precise fluid control at low dosing volumes, very often
within a range of a few microliters. Equally important is to have a fluid control system that will maintain
drift-free precision long-term, thus eliminating the need for recalibration, maintenance, costly service
calls and downtime.
FMI Valveless Piston Pump Technology
Accurately moving fluids through diagnostic instruments is most often accomplished using a metering or
dosing pump. Traditionally, a variety of fluid dispensing and control technologies have been used for
fluid control in diagnostic instrumentation, including peristaltic, diaphragm, syringe, and solenoid piston
pumps. Although these pump technologies have their merits, an innovative pump technology, the FMI
valveless piston pump has had a significant impact for the task of precision micro-fluidic control of
samples, reagents, buffers, wash and waste fluids.
The FMI Valveless Piston Pump is a piston pump that eliminates valves and elastomer components
typically associated with maintenance, accuracy and calibration concerns. The unique rotating and
reciprocating piston design eliminates the need for valves by having one moving part accomplish all fluid
control functions. In addition, all internal components are made from chemically–resistant, sapphirehard ceramics. These ceramic components are dimensionally stable and will not distort, stretch or
change shape over time. Pump technologies which rely on elastomers typically require routine
maintenance and recalibration over time (diaphragm and peristaltic). Internal pump components which
define the volume of the pumping chamber made from elastomers will eventually stretch, fatigue, and
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lose memory. This basically translates to the elastomer component (diaphragm or tubing) not returning
to its original dimension or shape. As a result, there is a gradual change the volume of the pumping
chamber which, in turn, causes variations in dosing volume and flow rate.
Syringe pumps, common in both medical diagnostic, as well as analytical instrumentation, basically
eliminate the concerns relating to accuracy drift as the result of using elastomers to define the pumping
chamber. However, syringe pumps have several moving parts in contact with the process fluid including
single and/or multi-port valves. For applications requiring continuous dosing and high throughput,
syringe pumps are typically configured in pairs. One pump is dispensing while the other pump of the pair
is filling and vise-versa. For these applications, one valveless piston pump can replace two syringe
pumps and their corresponding valves, actuators and driver boards. In addition, the primary seal of the
FMI valveless piston pump is the ultra-tight clearance between the ceramic piston and the mated
ceramic liner. This capillary seal is capable of handling pressures up to 100 psi and eliminates the need
for plunger o-rings and tips.
FMI Valveless Piston Pump Basics
The FMI valveless piston pump uses one moving part to accomplish both the pumping and valving
functions thereby eliminate check valves which are present in all other reciprocating (syringe,
diaphragm, bellows, solenoid piston) designs. The FMI valveless piston pump uses a unique rotating and
reciprocating ceramic piston, moving within a precision mated ceramic liner to accurately pump fluid in
one direction without allowing any backflow. The reciprocating action of the piston acts very similar to
that of a standard piston pump. As the piston moves back, it draws fluid into the pump chamber. As it
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moves forward, fluid is pushed out of the pump. However, what is truly unique is that in addition to
reciprocation, the piston also simultaneously and continuously rotates in one direction. The piston is
designed with a flat cut into the end closest to the inlet and outlet port (see figure 1). As the piston
rotates, the flat is alternately aligned with the inlet and outlet port, essentially functioning as a valve. At
no time are the inlet and outlet ports interconnected, and therefore the need for check valves is
eliminated. One complete synchronous rotation and reciprocation is required for each suction and
discharge cycle as shown below. An animation of continuous metering using the FMI valveless piston
pump principle can be found on the web site www.fmipump.com.
Illustration of FMI Valveless Pumping Principle
Adjustment of Dispense Volume
The piston displacement (or volume pumped per stroke) is variable and controlled by the angle of the
pump head relative to the drive. When the pump angle is zero, the pump head is in straight alignment
with the drive, the flow is zero. In this situation, there is no reciprocation and the piston is only rotating.
As the angle of the pump head increases above zero in either direction with respect to the drive, the
piston reciprocates, and fluid is moved through the pump (see figure 2). The greater the angle, the
greater the displacement per cycle (volume per stroke). Adjustment is infinite between zero and 100%
and a flow rate indicator provides for accurate and simple linear calibration. The pump is designed so
that at any angle and flow rate, the piston always bottoms for maximum bubble clearance. This is
especially important at very small dispenses and flow rates, as the presence of even a minute bubble will
significantly affect accuracy.
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Flow Rate Adjustment
KEY FEATURE SUMMARY
Valveless Design
The FMI valveless piston pump has only one moving part in the fluid path which functionally replaces
multiple check valves present in diaphragm, bellows, and traditional piston pumps, as well as multiple
valves, actuators, and drivers found in syringe designs. Even during normal operation, these will wear
over time and not seal properly allowing backflow. As a result, accuracy drifts and minimally the pumps
will require recalibration. Eventually, the valves need to be serviced.
Ceramic Internals
The FMI Valveless Piston Pump uses sapphire-hard ceramics for both the piston and mated liner. These
components are dimensionally stable in that they will not change shape or dimension over time.
Therefore, the pumping chamber remains stable for millions of dispenses without downtime or
recalibration.
Accuracy & Precision
Consistency in dispensing can be measured by monitoring both the accuracy and precision of the
dispenses. Accuracy is a comparison of the average value of the dispense volume compared to the
desired or target value. Precision is the range or degree of variation from dispense to dispense. Ideally,
metering and dosing should be both precise and accurate.
See below.
Precision & Accuracy
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Typical Long Term Precision
Versatile Design
The FMI valveless piston pump is available in a wide variety of configurations to meet a broad
range application requirements from small compact designs for OEM medical, diagnostic and
environmental instrumentation, to fully programmable laboratory dispensers and rugged
hazardous duty process pumps. Dual pump configurations are even available, ideal for
proportional mixing, dilution and dual channel production dispensing.
Additional Medical Applications:
The applications where the FMI valveless piston technology is used are numerous, ranging from microvolume reagent fluid control in OEM clinical diagnostic instrumentation, hemodialysis machines, and
automated immunoassay processing to precision production dispensing of cyclohexanone and other
solvents used in the manufacture of disposable medical component kits (I.V. tubing sets). FMI valveless
piston pumps are also used extensively for preparation of multi-well microtiter plates used in diagnostic
instrumentation; filling of pharmaceutical vials, ampules and syringes; dispensing monomers used for
disposable contact lens manufacturing; dispensing anticoagulants for coating of drug eluting stents;
dispensing electrolytes used to make button cell batteries for hearing aids. . . and much more.
In each application, the key features of the FMI valveless piston pump, including: one moving part,
ceramic internals, and valveless design, provide what medical manufacturers are looking for, that being
long term, drift-free accuracy and virtually no maintenance or downtime.
About Fluid Metering, Inc.
Located on Long Island about 30 from New York City, Fluid Metering, Inc. patented the first rotating and
reciprocating valveless piston pump and has been providing fluid control solutions for medical,
analytical, chemical process, and industrial applications for over 55 years. In each of these markets FMI
valveless piston pumps can be found from the laboratory to the production floor, incorporated into
OEM equipment and instrumentation, as well as process control and field installations.
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About the Author
Herb Werner has been the Marketing Manager for Fluid Metering, Inc. for 20 years with over 35 years
fluid control experience in chemical process, water treatment, medical & analytical instrumentation,
pharmaceutical, and semiconductor industries. He has a B.S in Environmental Biology and is an active
member of ISA, AWWA, & WEF societies.
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