Despatch LCC/LCD2-14-4 Oven Series with Protocol 3 - Manual (Page 21)

LCC/LCD2-14 Series Oven Owner’s Manual T HEORY OF O PERATION
Version 1 21
Copyright © 2013 by Despatch Industries.
All rights reserved. No part of the contents of this manual may be reproduced, copied or transmitted in any form or by any
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3.3.3.4. HEPA Filter Burn-off Process
HEPA filters contain a binder material which protects the filter media during production and
shipping. Smoke produced from burning this binder at elevated temperatures is undesirable
during normal oven operation. Burning off the binder will ensure a clean process at elevated
temperatures.
However, when the binder is burned out of the filter media, the filter becomes very fragile: too
fragile to withstand normal shipping and handling. For this reason, Despatch does not perform the
burn-off procedure. The burn-off process is not necessary at temperatures consistently under
180°C.
3.3.4. HEPA Filter Unit Replacement
Periodically replace the HEPA filter unit due to:

Resistance, or pressure drop, across the filter unit. Maximum level of resistance in inches
(water gauge) will vary depending upon the operation of the filter and the available fan
capacity. Adequate fan capacity must be available.

Loss of efficiency (leakage), determined from air-sampling measurements made downstream
of the filter unit.

Visible damage or rupture of the filter media in a unit.

Change in process application.

Excessive build-up of lint or combustible particulate matter on the filter unit.

Water droplets in airstream through filter, free water (RH = 100%), will saturate filter very
quickly and may cause burnout or holes in burned off filter media.
3.3.5. HEPA Filter: Magnehelic Pressure Gauge
The LCC Series oven is equipped with a Magnehelic pressure
gauge which measures the pressure in front of the HEPA filter
(Figure 6). As the filter becomes dirty, pressure increases.
Despatch recommends changing the filter when the pressure is 1”
w.c. greater than when the filter was first installed (Refer to
Section 4.3 for filter replacement).
Since pressure can be affected by many factors involved in the
installation, it is important to record the pressure of a new filter as
a baseline. Recorded pressure readings allow for new readings to
be periodically checked against this baseline. Use Table 6 for
recording this information (See Section 8.1 for a blank worksheet).
For a nitrogen atmosphere oven, pressure readings also give an indication of the integrity of the
seals. If the pressure recorded in Columns D or E decrease over time, inspect the oven seals.
Figure 6. Magnehelic Pressure
Gauge Measures Pressure in Front
of the HEPA Filter.