Properties of valve rotor materials
A variety of polymeric composites have been developed to meet a variety
of customer requirements for rotors, since no single material will perform
satisfactorily in all situations. This brief summary of each polymer’s
particular features and potential drawbacks is provided to allow the user
to make a more informed valve selection. Consult our technical specialists
for any additional questions. VICI polymer composites are proprietary
formulations: only the generic compound class can be discussed.
The specifications in the following discussions are for two position
valves. Multiposition valves generally have lower pressure and temperature
limits due to the more complex seal design. Actual specifications for each
valve series are shown on the appropriate pages throughout the valve
sections of the catalog. If a valve is to be used at a pressure higher
than the given standard, please contact the factory for ordering information.
Select a material to jump to specific discussions.
CTFE
Chlorotrifluoroethylene, is the generic name for the material produced
as Kel-F® and as Aclar®. It is very resistant to all chemicals except
THF and some halogenated solvents, and can be used at temperatures up to
100°C. Swells in ketones.
Valcon E
A polyaryletherketone/PTFE composite, the E material receives wide GC
use in what had previously been a problematic gap between the optimum
temperature ranges of P and T, and in HPLC applications where the temperature
requirement is higher than what can be handled by the H material and where
a lower pressure limit can be tolerated. (Standard specs are 400 psi at
225°C, but higher pressure ratings are possible at reduced temperatures.)
However, this polymer cannot be used in prolonged contact with high
concentrations of sulfuric and nitric acids, DMSO, THF, or liquid
methylene chloride.
Valco E2
A proprietary reinforced TFE composite, Valcon E2 works well at lower
pressures and is suitable for temperatures up to 75°C. This material is
resistant to most chemicals but should not be used in prolonged contact
with high concentrations of sulfuric and nitric acids, DMSO, or liquid
methylene chloride.
Valcon H
This composite, a carbon fiber reinforced, PTFE lubricated inert
engineering polymer, has long been the standard for typical HPLC
applications in which pressures are around 5000 psi and temperatures are
not more than 75°C. It is not unusual for these valves to be ordered for
use at 7000 psi, and less frequently for use at 10,000 psi. However, at
that point the lifetime may be shortened by as much as 50%.
Valcon H is the rotor material used in the W and UW series, where no
rotor material letter is added (as: C10W or AC6UW).
Valcon M
This material, basically a hydrocarbon in structure, is the most
impermeable to light gases of all the rotor materials currently available,
with wide acceptance in low-temperature (50°C maximum) trace gas
applications. Avoid use with aromatic hydrocarbons.
Valcon P
This composite, the majority of which is PTFE and carbon, was the
standard choice for most GC applications before the development of
Valcon E. (Standard specs are 400 psi at 175°C.) Routinely used at
1000 psi, 75°C, it can also be used at temperatures approaching 200°C
with decreased sealing tension; however, at that point Valcon E is
probably a better choice from a lifetime standpoint. Valcon E can replace
P in most applications.
Valcon T
This polyimide/PTFE/carbon composite has been used successfully for
many years and still cannot be surpassed when applications demand
operating temperatures in the 250°C – 350°C range. (Standard specs
for most series are 300 psi at 330°C.) However, at temperatures below
150°C there is a tendency for the seal material to stick to the valve
body, making the valve difficult to turn and causing the rotor to crack
in extreme cases. Literature provided at the time of purchase contains
instructions for reconditioning the material if this condition should
arise. The T material is susceptible to attack from steam, ammonia,
hydrazines (anhydrous liquids or vapor), primary and secondary amines,
and solutions having a pH of 10 or more. Chemical reagents which act as
powerful oxidizing agents (nitric acid, nitrogen tetroxide, etc.) must
also be avoided. Valcon T can be used in ”hot” GPC/SEC applications with
O-dichlorobenzene as a solvent.
Valcon TF
This is the series designation for a valve with a virgin PTFE seal.
Its mechanical characteristics are poor compared to the other choices,
but occasionally its use is dictated by the presence of oxidizing agents
too strong even for the R material.
Valcon X
This designation indicates a proprietary polyimide blend with chemical
properties similar to Valcon T, but with higher compressive strength.
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