Despatch Stackable LCC/LCD - Manual (Page 20)

T HEORY OF O PERATION Stackable LCC/LCD Oven Owner’s Manual
20 Version 26
Copyright © 2010 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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retrieval systems without the written permission of Despatch Industries, unless for purchaser's personal use.
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 4). 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 2 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.
Table 2. HEPA Filter Pressure Reading Worksheet.
A B C D E F
Date Comments Pressure
(inches of
water)
8
Pressure with:
150 SCFH (LCC1-
16); 200 SCFH
(LCC1-51) nitrogen
purge
9
Pressure with:
75 SCFH (LCC1-
16); 150 SCFH
(LCC1-51) nitrogen
maintain
9
Oven
Temperature
Typical
Values 2- 3” 1.5- 2” above value
in Column C
0.5- 1” above value
in Column C
60°C
Filter first
installed
8 With Purge and Maintain valves off for a nitrogen atmosphere oven. Cooling fan off for an air
atmosphere oven.
9
For a nitrogen atmosphere oven only.
Figure 4. Magnehelic Pressure
Gauge Measures Pressure in front of
the HEPA filter.