Glossary
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Adapter
A type of fitting which provides a method of joining two components of differing thread
types or systems.
Analytical column
A long narrow tube packed or coated with one of many available chemically diverse compounds
that can separate the components in a sample according to their boiling point, polarity, molecular
size, or combination thereof. A column of some kind is used with most chromatographic techniques.
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Backflush
The use of valving to reverse the flow through a column in order to "backflush" or purge
heavier components from the column. See application demonstrating backflush.
Biocompatibility
Defines the materials used in a system (i.e. fittings, tubing, and valves) that do not
change the bioactivity of the biological substances that come into contact with the surface
of these materials. (Note that in chromatographic systems, the tubing and column contribute
over 99% of the surface area and the valves and fittings are insignificant.)
Bore
The diameter of the minimum orifice through the fitting; see capillary bore,
through-type bore, and large bore.
Bulkhead fitting
A type of fitting in which the fitting body is inserted through an instrument panel or
mounting bracket, to which it is affixed with a mounting nut. The Valco fitting body is
uniquely undercut so that it "bites" into the panel when the mounting nut is tightened,
eliminating the need for a lock washer.
Butt connection
A type of connection in which the two tube ends are directly and squarely in contact,
usually effected with a through-type union. Typically used with fused silica connections,
or small bore metal tubing.
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Cap
A cap is used to dead-end a piece of tubing with a nut and ferrule attached.
Capillary bore
The smallest available standard orifice in a given fitting design (usually 0.25 mm).
Typically denoted by suffix "C" in the product number.
Compression fitting
A style of fitting in which a threaded nut compresses a tapered ferrule onto tubing
as the nut is tightened. Valco metal ferrules cut a ring into the tubing wall while
polymer types rely on surface compression to form a seal.
Connecting volume
The volume between two or more connections. This may be cleanly swept, thus not contributing
to peak distortion, or may be “dead volume“ such as that found in fittings with larger bores
than the connecting tubing.
Cross
A type of distribution fitting which connects four pieces of tubing, arranging them in the
pattern of a cross.
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Dead volume
Any volume which a component introduces to a system that is not cleanly swept and relies
on diffusion to clear the space. See connecting volume.
Detail
See Fitting detail
Distribution fitting
A generic term for tees, crosses, and manifolds, used to provide multiple access points
to "distribute" a gas or liquid through a system. CAUTION! Using a distribution fitting
in reverse to coalesce multiple streams may create dead volume. Special manifolds are
available for this application.
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Female Nut
A type of compression fitting in which the nut has female threads.
FIA
Flow Injection Analysis. A simple and versatile analytical technique for
automating wet chemical analyses based on the manipulation of a sample zone
formed from the injection of the sample into a continuous stream of fluid used as a carrier.
Ferrule
One of the components of a compression fitting; the conical piece of metal or plastic
that compresses onto the tube as it is forced into a tapered seat. Valco metal ferrules
are unique in that they attach to and seal at the tube by cutting a shallow ring into it,
instead of by actually swaging it. This is preferable since it introduces no flow restriction.
Filter
A type of union or reducing union which traps the particulates in a stream. The filtering
element is typically a mesh screen or sintered frit.
Fitting detail
One of the components of a compression fitting; if the tube, nut, and ferrule comprise the male
part of the fitting, the fitting detail is the female part. It in-cludes the threads for the nut,
the tapered ferrule seat, and the pilot.
Flanged Nut
A type of nut used with fluoropolymer tubing (PTFE, FEP) in which a flange is made at the
tube end. Connections are made at the flange either by compressing the flange into a flat detail
(typically 1/4"-28 threaded) or by butting two flanges together. A special flanging tool forms the
flanges.
Flangeless Nut
Similar in application to the flanged nut, but the flange is not required. A ferrule system is
used which grips/compresses the tube. This fitting type can be used with virtually any polymeric
tubing since the tube end does not have to be formed, but simply square cut. Typically used in
1/4"-28 threaded fitting details, it is usually interchangeable with flanged nut.
Frit
A filter element typically made of stainless, Hastelloy, Titanium, or polymers, usually 0.75 mm
or 1 mm thick. Frits may provide better filtration than screens, but because they are thicker
there is greater mixing potential, and they typically result in increased pressure drop.
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GC
Gas Chromatography. An analytical method incorporating an injection system, analytical column,
controlled temperature zone, and detector. An inert carrier gas moves the sample through the
column, which separates the sample components into discrete bands which are measured as they
pass through the detector.
Guard column
A column used in series between the injector and analytical column to prevent certain types
of components from enteringthe analytical column.
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HPLC
High Performance Liquid Chromatography. An analytical system consisting of an
injector, pump, analytical column, and detector. Using a liquid mobile phase, the
sample is pumped through the column, where it is separated into discrete sample component
bands which are detected and measured as the bands elute from the column.
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ID
Internal diameter.
Inert
Technically, unreactive with other substances; however, in the instrumentation field,
"inert" is a relative term. Often polymers are termed inert but are soluble in some fluids
and can react with some compounds.
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LC
Liquid Chromatography. Any of a variety of low to medium pressure techniques which use
a liquid mobile phase as the carrier to move sample. Similar to HPLC.
Large bore
A bore that is larger than the standard for a given fitting; a fitting ordered with a
large bore will have a larger flow orifice than the standard or capillary bore fitting
of the same design. Denoted by suffix "L" in the product number.
Luer adapter
An adapter that connects a tapered luer fitting (square nib) of a syringe to a tube
or tube fitting.
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Male Nut
A type of compression fitting in which the nut has male threads.
Make up
The point at which a ferrule, nut, and tube are assembled in the fashion which
will effect a leak-free seal. In most compression fittings, that is accomplished by
compressing the tube with the small end of the ferrule. With Valco metal ferrules, the
ferrule usually makes up on the tube by cutting a shallow ring in it.
Manifold
A type of distribution fitting in which a single source is directed to multiple outlets,
or vice versa. Caution! Using a common distribution fitting in reverse to merge multiple
streams may create dead volume. Special manifolds are available for this application.
Microbore column
A liquid chromatography column of narrow bore (typically 2 mm or less) for improved resolution.
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NPT
National Pipe Thread; a standardized tapered pipe fitting. See pipe thread.
Nut
The tensioning component of a compression fitting. As the threaded nut is tightened into
the fitting detail, it pushes the ferrule forward into the tapered ferrule seat, causing
it to make up on the tube.
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Pilot
The tubing which extends beyond the ferrule in a made-up fitting, or the integral portion
of a ZRF internal reducing ferrule which extends beyond the ferrule. See also pilot depth.
Pilot depth
The length of the tubing diameter cavity beyond the tapered ferrule seat within a fitting detail.
Valco fitting pilot depths are tightly controlled to facilitate the interchange ability of components
without the risk of leaks or dead volume.
Pipe thread
The external or internal threads of a fitting designed to effect a metal-to-metal seal on the conical
thread faces. This type of fitting does not "bottom out" in the detail. Typically used with Teflon
tape or other compound to lubricate the threads; however, since the diffusion rate of air components
through the Teflon tape is considerable, pipe fittings should not be used in systems where leakage
rates are critical.
Port
The connection, orifice, seal, or septum, etc. through which sample may be added (injected) or withdrawn.
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Reducing ferrule
A ferrule which allows a smaller tube to be used in a fitting detail designed
for a larger tube. Caution should be taken if standard reducing ferrules (RF) without
integral pilots are used, since dead volume may be created in the fitting pilot depth.
Reducing union
A fitting which joins two tubes of different ODs. The bore of the fitting should typically
match the ID of the smaller tube.
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Tee
A type of distribution fitting which connects three pieces of tubing,
arranging them in the pattern of a "T".
Through-type bore
A bore which is slightly larger than the OD of the tubing which is used
with the given fitting. A union with a through-type bore allows the tube
ends to butt directly together, or for one tube to run completely through
the fitting. Denoted by suffix "T" in the product number. In order to assure
correct pilot lengths, we recommend that ferrules be made up on the tubing in
a standard union.
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Union
A fitting for connecting two pieces of tubing of the same OD, or different
OD’s. (See also reducing union)
Female union: a type of compression fitting in which the fitting
body has female threads. Also referred to as an internal union.
Male union: a type of compression fitting in which the fitting body has male threads.
Also referred to as an external union.
Unswept volume
The volume of any portion of a fitting which is in the flowpath but which is a
different diameter than the primary flow orifice through the tubing/fitting assembly,
or any area not directly swept by the fluid flow. This can also be known as "dead volume"
if it is very poorly swept.
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Wetted surfaces
The surfaces which are contacted by the sample stream.
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Y
A type of distribution fitting which connects three pieces of tubing,
arranging them in the pattern of a "Y". Occasionally referred to as a "wye".
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ZDV
Abbreviation for zero dead volume.
Zero dead volume (ZDV)
Describes a connection which does not add volume to the system beyond what an
extension of tubing would in its place.
Zero volume
While often used interchangeably with zero dead volume, it ideally describes a
fitting design in which there is no internal volume, such as a through-type union
designed to butt-fit two pieces of tubing.
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