Out-of-Stack Diluter Seal Upgrade
To Eliminate Leakage and Sample Contamination
original EPM Environmental Model 797.380 Series OOS (Out Of
Stack Diluting Sampler) used a Kalrez® O-ring to create
the seal between the diluter tip and the inner flange assembly.
This configuration, using a Kalrez® O-ring, will limit
the maximum operating temperature of the instrument to 572°F
application requirements became more demanding of greater
temperature flexibility, it was decided to introduce a new
Series OOS design having higher inlet sample temperature and/or
heater set-point temperature capabilities.
1999, EPM had made a design change to the standard OOS Diluting
Sampler to accomplish this. The design change consisted of
Elimination of the Kalrez® O-ring from the design. In
its place would be a 3/4" Swagelok® ferrule configuration
2. Modification to the diluter side of the inner flange assembly
to accept the ferrules that are permanently swaged to the
3. Larger inside diameter of the heater mantle, so that the
diluter (with 3/4" Swagelok® nut permanently attached)
could pass through it.
4. Sleeve/housing attached to the outside of the diluter,
to eliminate the resulting gap between the diluter and larger
ID of the heater mantle.
5. Modification to the knurled nut (hand wheel), so that it
fits over the 3/4" Swagelok® nut.
design change allowed for the maximum operating temperature
(sample gas temperature and/or heater set-point temperature)
of up to 750°F (400°C). The new model became EPM's
standard OOS known as the Model 797.380-S Series ("-S"
in the model number denotes "Swagelok®" type
diluter tip seal).
the design change was proven to be successful in high temperature
applications, and applications where cold process or ambient
conditions required higher set-point temperatures, some issues
have surfaced with regard to using the Swagelok® seal
issues are as follows:
Leakage around the diluter tip which results in ambient air
being drawn into the sample chamber via the bypass pump and
contaminating the sample gas.
2. Difficulty re-tightening the Swagelok® nut to the full
3/4 turn from finger tight (per Swagelok® specifications).
3. Requirement for routine leak-tight testing that is time
consuming as the system is not closed-loop.
4. Cross-threading of the modified knurled nut and threads
of the inner flange assembly.
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