270NH3.MAN.REVD.062019
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9.0
Maintenance
CHANGING THE FILTER
CAUTION: THIS PROCEDURE CAN CAUSE SEVERE BURNS. USE PROPER
PROTECTION.
Changing the filter in the Model 270 Heated Filter Assembly is extremely easy. Using gloves to protect the
hand, grasp the cap on the end of the filter body opposite the probe and turn it counterclockwise. The cover
may be hot to the touch and may cause burns to the hand if not protected. Removing the cover exposes the
filter. The cover is secured to the assembly with a retainer chain. Reach into the heated oven with pliers to
pull out the old filter.
Inspect the O-Rings which are at each end of the filter to ensure they are still elastic and will seal the filter.
Replace O-Rings if they are charred or deformed.
Replace the filter with a new one, again handling it with pliers. Ensure that the filter is pushed in the center of
the oven so that it is in contact with the O-Ring on the far end of the filter. Screw the cap back on the filter
body. The filter replacement procedure is complete.
NH
3
CONVERTER
The NH
3
Converter requires relatively little maintenance, but over a long period of time (years), the
effectiveness can drop off due to oil and oxidation coatings on the internal components. This is measurable
by comparing the cal gas analysis through both sample ports. When the converter effectiveness is no longer
acceptable, a replacement chamber may be installed.
Complete a full shutdown sequence and include enough time for adequate cool down. The canister starts at
over 1250°F and is well insulated, so cool down may take up to 24 hours. Pumping instrument air through the
canister will reduce cool down time.
1. Unbuckle the ceramic heater/insulator strap and open the front half of the unit. There should be
adequate room to leave the heater wired up and still perform the swap.
2. Slide the thermocouple down and out of the canister.
3. Loosen the fittings from the canister tubes at the bulkhead wall and remove the canister.
It is not recommended to perform maintenance on any other part of the converter assembly.
