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.


The use of valving to reverse the flow through a column in order to "backflush" or purge heavier components from the column.

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.

The diameter of the minimum orifice through the fitting.
See definitions for 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.


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.

Clamp ring
Adjustable ring for clamping the valve or standoff assembly onto an actuator, knob, or instrument panel.

Closemount hardware
All the hardware required to mount a valve directly onto the fac of an air, standard electric, or microelectric actuator, providing the most direct, shortest attachment of valve to actuator.

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.

A type of distribution fitting which connects four pieces of tubing, arranging them in the pattern of a cross.



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.

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.


External fitting
A type of compression fitting in which the fitting body has male threads; an external nut has female threads.


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.

Female nut
A nut with female threads; also called external nut.

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.

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.

Fingertight fitting
A fingertight fitting is a knurled or winged nut which is hand tightened to compress the ferrule. Note: Polymeric ferrules rely on surface compression to form a seal and hold the tube by friction.


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 includes the threads for the nut, the tapered ferrule seat, and the pilot.
See compression fitting.

Valco fitting details have the perfect shape, with a smooth transition from the ferrule seat into the cylindrical and threaded part. Many other fitting details are poor in design where the ferrule is forced in a too shallow ferrule seat. The result is a "nicked" ferrule which can no longer apply its sealing force to the front of the ferrule.

Flanged fitting
A type of fitting 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 fitting
Similar in application to the flanged fitting, 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 fittings, it is usually interchangeable with flanged fittings.

A filter element typically made of stainless, Hastelloy, Titanium, or polymers, usually 0.75 mm or 1 mm thick. Nanovolume frits, at 0.25 mm (.010") thick, add minimum volume for nanovolume filtration. 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.


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 entering the analytical column.


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.


Internal diameter.

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.

Internal fitting
A type of compression fitting in which the fitting body has female threads; an internal nut has male threads.


The design which enables multiposition microelectric actuators to self-align. A specially designed clamp ring and standoff assembly key together with the microelectric actuator and the valve to locate position 1.


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.


Male nut
A nut with 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.

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.


National Pipe Thread; a standardized tapered pipe fitting. See pipe thread.

Nanobore generally refers to components with bore sizes less than 250 µm (0.010").

The registered trademark referring to VICI Valco's line of nanobore fittings and injectors.

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.


Outside diameter.



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, below.

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 interchangeability 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.

The connection, orifice, seal, or septum, etc. through which sample may be added (injected) or withdrawn.

Position feedback
Hardware which provides a contact closure for the remote start of a chromatograph or data system.


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.

The internal rotating part of a Valco or Cheminert valve. It contains the engraved slots which connect the ports on the stator or cap.


Supercritical Fluid Extraction.
An extraction technique using a fluid in its supercritical state as the extraction medium. Some liquids and mixtures maintained above a critical temperature and pressure exhibit properties of both the liquid and gas phases of the element. These are defined as supercritical. CO2 is a common supercritical fluid. Extreme caution must be used with supercritical CO2, since uncontrolled expansion (leaks) can be very hazardous due to the substantial stored energy.

Supercritical Fluid Chromatography.
An analytical technique using a supercritical fluid (see SFE) as the mobile phase/carrier.

A replaceable filter element generally made of Type 316 stainless steel, usually 0.003" thick. Screens clog less frequently than frits, and because they are thinner there is less mixing; however, they are less effective filters.

Any force on the valve rotor other than the proper rotational force along the axis of the rotor, often resulting in leakage or increased wear. It is typically caused by actuation misalignment, over-rotation, or improper mounting of the valve.

Standard bore
A bore which was chosen as the standard for a particular fitting, typically based on the most common tubing ID used with that fitting.

An extension between a valve and actuator which allows the valve to be installed in a different temperature zone from the actuator. Standoffs come in several different lengths.

Standoff assembly
All the hardware required to allow a valve to be mounted in an oven or heated zone while the actuator or knob remains outside the heated zone. Standard lengths are 2", 3", 4", and 6.

Standoff mounting hardware
The clamp ring and screws necessary to mount a valve and standoff assembly onto an actuator.

The stationary component of a valve. Typically, it contains the fittings as well as one of the fluid sealing surfaces. In Valco valves, the stator is called the valve body.


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.


A fitting for connecting two pieces of tubing of the same OD.

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.


VICI® is an acronym for Valco Instruments Company Inc.
VICI now defines multiple companies which manufacture various products for the analytical industry.


Wetted surfaces
The surfaces which are contacted by the sample stream.


Y ("Wye")
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".



Zero dead volume. See definition below.

Zero dead volume
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.