Teledyne 9110EH - Nitrogen Oxides Analyzer - Manual (Page 171)

Model 9110EH Instruction Manual Instrument Maintenance
9.3.10. Cleaning or Changing Critical Flow Orifices
There are several critical flow orifices installed in the M9110EH, Figure 9-6 shows one of the
two most important orifice assemblies, located on the reaction cell. Refer to Section 10.2.9
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 M9110EH 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 clean or replace a critical flow orifice, do the following:
• Turn off power to the instrument and vacuum pump. Remove the analyzer cover and
locate the reaction cell (Figure 9-6, Figure 11-7 and Figure 3-7).
• Unscrew the 1/8” sample and ozone air tubes from the reaction cell
• For orifices on the reaction cell (Figure 9-6): Unscrew the orifice holder with a 9/16”
wrench. This part holds all components of the critical flow assembly as shown in
Figure 9-7. Appendix B contains a list of spare part numbers.
• For orifices in the vacuum manifold: the assembly is similar to the one shown in
Figure 9-7, but without the orifice holder and bottom O-ring
and with an NPT fitting in place of the fitting. After taking off the
connecting tube, unscrew the NPT fitting.
• Take out the components of the assembly: a spring, a sintered filter, two O-rings
and the orifice. For the vacuum manifold only, you may need to use a scribe or
pressure from the vacuum port to get the parts out of the manifold.
• Discard the two O-rings and the sintered filter and clean the critical flow orifice in a
ultrasonic cleaner for about 30 minutes using methanol. Let the part dry.
• Re-assemble the parts as shown in Figure 9-7 and re-connect them to the reaction
cell manifold or the vacuum manifold.
• Reconnect all tubing, power up the analyzer and pump and - after a warm-up period
of 30 minutes, carry out a leak test as described in Section 11.5.1.
M9110EH Rev 0 157