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general reference
Glossary
slot in rotor
Rotor visible in cutaway valve
port id
(bore size)
rotor
TUBING
MALE NUT
(Internal)
FERRULE
PILOT
BODY OF
FITTING
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 PTFE tape or other compound to lubricate the
threads; however, since the diffusion rate of air components
through the PTFE 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sample may be added (injected) or withdrawn.
R
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.
Rotor:
the internal rotating part of a Valco valve. It contains the
engraved slots which connect the ports on the stator or cap.
S
SFE:
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. CO
2
is a common supercritical fluid. Extreme caution must be used
with supercritical CO
2
, since uncontrolled expansion (leaks) can
be very hazardous due to the substantial stored energy.
SFC:
Supercritical Fluid Chromatography. An analytical technique
using a supercritical fluid (see SFE) as the mobile phase/carrier.
Screen:
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.
Sideloading:
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.
M
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.
N
Nanovolume:
nanovolume generally refers to components with
bore sizes less than 250 µm (0.010").
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.
O
OD:
outside diameter.
P
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
.
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