PrimeLine™ Replacement
Piston Seals
Selecting the Best Material for Your Application
ASI
offers both UHMW-PE and Teflon compounds for pump seal jackets. The
selection of the best material depends on a number of factors, which
are discussed below.
UHMW-PE Compound
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This material is based on ultra-high molecular
weight polyethylene, and is compounded with other proprietary polymers
to provide better lubricity and solvent resistance than pure UHMW-PE.
This material is a self-lubricating compound that exhibits excellent
wear characteristics, low coefficient of friction, and good resistance
to cold-flow (extrusion). It is often used for "dry" bearings and
seals, where lubrication by oil or other fluids is not permitted.
It is resistant to most HPLC solvents except for methylene chloride
and Toluene. UHMW-PE seals should only be used intermittently when
using these solvents in 100 % concentration.
ASI
offers two different formulations of this material. One is
a gold color and the other is white. The gold material is slightly
stiffer than the white material, while the white material exhibits
a slightly lower coefficient of friction. The formulation that we
feel is most suitable for a specific pump model is the only formulation
of UHMW-PE that we offer for that pump model. There are many different
UHMW-PE formulations that appear the same color _ but they are not
all the same. We have subjected our materials to thousands of hours
of testing to prove them out, and we are confident of their superior
performance.
Teflon® Compound
-
This material is Teflon (PTFE) with a filler
added to it for the purpose of increasing resistance to cold flow
and improving wear characteristics. It is absolutely inert to any
hplc solvent, but does not have the high resistance to wear and
cold-flow that the UHMW-PE compounds have. It is more flexible that
UHMW-PE, and therefore will conform better with pistons that are
not aligned well, or which are worn flat. The color of our formulation
is black. There are dozens of Teflon compounds, many of which are
black, but they are not the all same. Some offer an extremely low
coefficient of friction but wear rapidly, while others last longer
but can rapidly wear the sapphire piston (such as ceramic filled
Teflon). The selection of the Teflon compound that we use is based
on thousands of hours of testing of compounds from several different
suppliers, and we are confident that it offers the best performance.
Conclusion
-
In general we recommend using our UHMW-PE compound.
It generates less wear material than Teflon, tends to act as a better
bearing to help align the piston, and has a much longer service
life than Teflon. Always inspect the piston for signs of scoring
or wear when replacing seals. If your piston is worn or scratched-
replace it- because nothing will destroy a seal faster than
a worn or scratched piston. Refer to the section on pistons for
advice on detecting a worn piston.
Piston Seal Installation
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It is good practice to clean the pump head when
replacing seals. Seal wear material will collect on the wetted surfaces
of the head, and these will contaminate check valves and other downstream
components. Always wet the seal and inside of the pump head with
Isopropanol prior to installing the seal.
Please refer to the "Maintenance
and Trouble Shooting Tips" on piston seals for more information.
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