Molecular Sieve Traps
Molecular sieve traps containing type 13X synthetic zeolite effectively prevent oil backstreaming and trap water vapors at room temperature.Type 13X zeolite will adsorb molecules with critical diameters up to 10 angstrom. The sieve charge can be reactivated by baking out in place when a base vacuum cannot be achieved. A valve should be used to isolate the evolved gas from the system during the bakeout cycle. During bakeout a mechanical pump removes the evolved gases from the sieve trapping material. To minimize down-time, bakeouts can be conducted, with the aid of a timer, during system off-hours. Oils trapped by the sieve material will not be evolved by baking. Periodic replacement of the sieve material is required whenever the sieve material exhibits evidence of hydrocarbon saturation as determined by empirical observation. The sieve trapping material is easily replaced through a port fitted to the top of the trap. Molecular sieve traps can be mounted in a vertical or horizontal position. A trap’s built-in heater requires customer wiring to a 115VAC wall outlet. Once turned on, the heater reaches and maintains a self-regulated and constant 150°C temperature. Bakeout time depends on the amount of water vapor loading of the zeolite and can range from 4 to 12 hours. 

Coaxial Traps
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 evaluated. 

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.