Coaxial foreline traps offer easy maintenance and room temperature operation, they
require no bakeout or cooling and are virtually maintenance-free. They are ideally
suited for trapping roughing pump hydrocarbons from backstreaming into a
vacuum system. Single piece coaxial foreline traps contain absorbent filter
cartridges with a bronze wool element. This filter element is permanently sealed inside the trap’s body
and can’t be removed or replaced. These traps are serviced by replacing them with a
spare unit while cleaning the contaminated trap. Single piece traps are available in 4"
and 6" body diameters. In contrast to the single piece units, the two piece coaxial
foreline traps offer a wider selection of filter element materials. Filter
elements for a two piece trap are removable stainless steel screen cartridges filled with
copper, stainless steel or bronze wools, activated alumina, activated carbon or dual
element absorbent materials. During operation, pump oil coalesces on the
element and returns to the pump. Activated alumina effectively adsorbs acids and water
vapor while activated carbon adsorbs organics and water vapor. Filter cartridges
are quickly and easily replaced by removing the banded clamp that fastens
the two-piece body. MDC recommends keeping a spare element on-hand for a quick change to
minimize down time. Reusable elements may be cleaned and ready for the next
exchange. Note that filter elements are not included with trap assemblies
and must be ordered separately. Two piece traps are offered with 2", 4", 6" and 8" body
diameters. All coaxial trap bodies are made of type 304 stainless steel and are offered
with a choice of hose or flange style connections. Del-Seal™ CF metal
seal flange connections have one fixed and one rotatable flange for alignment purposes.
Kwik-Flange™ ISO KF and Large-Flange™ ISO LF flanges are clamp-style. Hose
connections may also be welded, but permanent installation must be carefully
Contaminated traps may be cleaned with a solvent and allowed to dry before
replacing into service. MDC recommends having a spare trap or filter element available for
rapid replacement to minimize down time during the cleaning process.
Liquid Nitrogen Traps
Liquid nitrogen traps remove condensables before they enter the pump or backstream
from the pump to the vacuum system.Water trapping by the liquid nitrogen cooled
surface is complete and permanent.
Liquid nitrogen traps can be fitted with a customer-supplied coolant level controller to
automatically replenish consumed liquid nitrogen.
In general, trap performance will vary with the specific application, usage, number of
process cycles and relative humidity in the region. One cycle per day in
an R&D application could provide approximately six months of maintenance free service.
Production type applications will require more stringent preventative maintenance
programs tailored to a specific application.