Teledyne 9110TH - Nitrogen Oxides Analyzer - Manual (Page 218)

Model 9110TH NOx Analyzer Instrument Maintenance
Teledyne Analytical Instruments 198
10. After cleaning, the analyzer span response may drop 10 - 15% in the first 10 days
as the reaction cell window conditions. This is normal and does not require another
cleaning.
6.4.6. CHANGING CRITICAL FLOW ORIFICES
There are several critical flow orifices installed in the 9110TH/M, Figure 6-4 shows one
of the two most important orifice assemblies, located on the reaction cell. Refer to
Section 8.3.3 for a detailed description on functionality and locations. Despite the fact
that these flow restrictors are protected by sintered stainless steel filters, they can, on
occasion, clog up, particularly if the instrument is operated without sample filter or in an
environment with very fine, sub-micron particle-size dust.
The 9110TH/M introduces an orifice holder that makes changing the orifice very easy.
In fact, it is recommended to keep spare orifice holder assemblies at hand to minimize
downtime and swap orifices in a matter of a few minutes. Appendix B lists several
complete spare part kits for this purpose.
To replace a critical flow orifice, do the following:
1. Turn off power to the instrument and vacuum pump. Remove the analyzer cover
and locate the reaction cell (Figure 3-7 for location in chassis, and Figure 6-4 for
exploded view of assembly).
2. Unscrew the 1/8” sample and ozone air tubes from the reaction cell
3. For orifices on the reaction cell (Figure 6-4): Unscrew the orifice holder with a 9/16”
wrench. This part holds all components of the critical flow assembly as shown in
Figure 6-5. Appendix B contains a list of spare part numbers.
4. For orifices in the vacuum manifold: the assembly is similar to the one shown in
Figure 6-5, but without the orifice holder, part number 04090, and bottom O-ring
OR34 and with an NPT fitting in place of the FT 10 fitting. After taking off the
connecting tube, unscrew the NPT fitting.
Figure 6-5: Critical Flow Orifice Assembly